EyeLink Usability / Applied Publications
All EyeLink usability and applied research publications up until 2023 (with some early 2024s) are listed below by year. You can search the publications using keywords such as Driving, Sport, Workload, etc. You can also search for individual author names. If we missed any EyeLink usability or applied article, please email us!
2014 |
Stéphanie M. Morand; Monika Harvey; Marie-Hélène Grosbras Parieto-occipital cortex shows early target selection to faces in a reflexive orienting task Journal Article In: Cerebral Cortex, vol. 24, no. 4, pp. 898–907, 2014. @article{Morand2014, It is well established that human faces induce stronger involuntary orienting responses than other visual objects. Yet, the timing of this preferential orienting response at the neural level is still unknown. Here, we used an antisaccade paradigm to investigate the neural dynamics preceding the onset of reflexive and voluntary saccades elicited by human faces and nonface visual objects, normalized for their global low-level visual properties. High-density event-related potentials (ERPs) were recorded in observers as they performed interleaved pro- and antisaccades toward a lateralized target. For reflexive saccades, we report an ERP modulation specific to faces as early as 40–60 ms following stimulus onset over parieto-occipital sites, further predicting the speed of saccade execution. This was not linked to differences in the programming of the saccadic eye movements, as it occurred early in time. For the first time, we present electrophysiological evidence of early target selection to faces in reflexive orienting responses over parieto-occipital cortex that facilitates the triggering of saccades toward faces. We argue for a 2-stage process in the representation of a face in involuntary spatial orienting with an initial, rapid implicit processing of the visual properties of a face, followed by subsequent stimulus categorization depicted by the N170 component. |
Dan Nemrodov; Thomas Anderson; Frank F. Preston; Roxane J. Itier Early sensitivity for eyes within faces: A new neuronal account of holistic and featural processing Journal Article In: NeuroImage, vol. 97, pp. 81–94, 2014. @article{Nemrodov2014, Eyes are central to face processing however their role in early face encoding as reflected by the N170 ERP component is unclear. Using eye tracking to enforce fixation on specific facial features, we found that the N170 was larger for fixation on the eyes compared to fixation on the forehead, nasion, nose or mouth, which all yielded similar amplitudes. This eye sensitivity was seen in both upright and inverted faces and was lost in eyeless faces, demonstrating it was due to the presence of eyes at fovea. Upright eyeless faces elicited largest N170 at nose fixation. Importantly, the N170 face inversion effect (FIE) was strongly attenuated in eyeless faces when fixation was on the eyes but was less attenuated for nose fixation and was normal when fixation was on the mouth. These results suggest the impact of eye removal on the N170 FIE is a function of the angular distance between the fixated feature and the eye location. We propose the Lateral Inhibition, Face Template and Eye Detector based (LIFTED) model which accounts for all the present N170 results including the FIE and its interaction with eye removal. Although eyes elicit the largest N170 response, reflecting the activity of an eye detector, the processing of upright faces is holistic and entails an inhibitory mechanism from neurons coding parafoveal information onto neurons coding foveal information. The LIFTED model provides a neuronal account of holistic and featural processing involved in upright and inverted faces and offers precise predictions for further testing. |
Haijing Niu; Hao Li; Li Sun; Yongming Su; Jing Huang; Yan Song Visual learning alters the spontaneous activity of the resting human brain: An fNIRS study Journal Article In: BioMed Research International, pp. 1–9, 2014. @article{Niu2014, Resting-state functional connectivity (RSFC) has been widely used to investigate spontaneous brain activity that exhibits correlated fluctuations. RSFC has been found to be changed along the developmental course and after learning. Here, we investigated whether and how visual learning modified the resting oxygenated hemoglobin (HbO) functional brain connectivity by using functional near-infrared spectroscopy (fNIRS). We demonstrate that after five days of training on an orientation discrimination task constrained to the right visual field, resting HbO functional connectivity and directed mutual interaction between high-level visual cortex and frontal/central areas involved in the top-down control were significantly modified. Moreover, these changes, which correlated with the degree of perceptual learning, were not limited to the trained left visual cortex. We conclude that the resting oxygenated hemoglobin functional connectivity could be used as a predictor of visual learning, supporting the involvement of high-level visual cortex and the involvement of frontal/central cortex during visual perceptual learning. |
Daniel Baldauf; Robert Desimone Neural mechanisms of object-based attention Journal Article In: Science, vol. 344, no. 6182, pp. 424–427, 2014. @article{Baldauf2014, How we attend to objects and their features that cannot be separated by location is not understood. We presented two temporally and spatially overlapping streams of objects, faces versus houses, and used magnetoencephalography and functional magnetic resonance imaging to separate neuronal responses to attended and unattended objects. Attention to faces versus houses enhanced the sensory responses in the fusiform face area (FFA) and parahippocampal place area (PPA), respectively. The increases in sensory responses were accompanied by induced gamma synchrony between the inferior frontal junction, IFJ, and either FFA or PPA, depending on which object was attended. The IFJ appeared to be the driver of the synchrony, as gamma phases were advanced by 20 ms in IFJ compared to FFA or PPA. Thus, the IFJ may direct the flow of visual processing during object-based attention, at least in part through coupled oscillations with specialized areas such as FFA and PPA. W |
Lysianne Beynel; Alan Chauvin; Nathalie Guyader; Sylvain Harquel; Thierry Bougerol; Christian Marendaz; David Szekely What saccadic eye movements tell us about TMS-induced neuromodulation of the DLPFC and mood changes: A pilot study in bipolar disorders Journal Article In: Frontiers in Integrative Neuroscience, vol. 8, pp. 65, 2014. @article{Beynel2014, The study assumed that the antisaccade (AS) task is a relevant psychophysical tool to assess (i) short-term neuromodulation of the dorsolateral prefrontal cortex (DLPFC) induced by intermittent theta burst stimulation (iTBS); and (ii) mood change occurring during the course of the treatment. Saccadic inhibition is known to strongly involve the DLPFC, whose neuromodulation with iTBS requires less stimulation time and lower stimulation intensity, as well as results in longer aftereffects than the conventional repetitive transcranial magnetic stimulation (rTMS). Active or sham iTBS was applied every day for 3 weeks over the left DLPFC of 12 drug-resistant bipolar depressed patients. To assess the iTBS-induced short-term neuromodulation, the saccadic task was performed just before (S1) and just after (S2) the iTBS session, the first day of each week. Mood was evaluated through Montgomery and Asberg Depression Rating Scale (MADRS) scores and the difference in scores between the beginning and the end of treatment was correlated with AS performance change between these two periods. As expected, only patients from the active group improved their performance from S1 to S2 and mood improvement was significantly correlated with AS performance improvement. In addition, the AS task also discriminated depressive bipolar patients from healthy control subjects. Therefore, the AS task could be a relevant and useful tool for clinicians to assess if the Transcranial magnetic stimulation (TMS)-induced short-term neuromodulation of the DLPFC occurs as well as a “trait vs. state” objective marker of depressive mood disorder. |
Timothy Leffel; Miriam Lauter; Masha Westerlund; Liina Pylkkänen Restrictive vs. non-restrictive composition: A magnetoencephalography study Journal Article In: Language, Cognition and Neuroscience, vol. 29, no. 10, pp. 1191–1204, 2014. @article{Leffel2014, Recent research on the brain mechanisms underlying language processing has implicated the left anterior temporal lobe (LATL) as a central region for the composition of simple phrases. Because these studies typically present their critical stimuli without contextual information, the sensitivity of LATL responses to contextual factors is unknown. In this magnetoencephalography (MEG) study, we employed a simple question-answer paradigm to manipulate whether a prenominal adjective or determiner is interpreted restrictively, i.e., as limiting the set of entities under discussion. Our results show that the LATL is sensitive to restriction, with restrictive composition eliciting higher responses than non-restrictive composition. However, this effect was only observed when the restricting element was a determiner, adjectival stimuli showing the opposite pattern, which we hypothesise to be driven by the special pragmatic properties of non-restrictive adjectives. Overall, our results demonstrate a robust sensitivity of the LATL to high level contextual and potentially also pragmatic factors. |
Benjamin D. Lester; Paul Dassonville The role of the right superior parietal lobule in processing visual context for the establishment of the egocentric reference frame Journal Article In: Journal of Cognitive Neuroscience, vol. 26, no. 10, pp. 2201–2209, 2014. @article{Lester2014, Visual cues contribute to the creation of an observerʼs ego- centric reference frame, within which the locations and orien- tations of objects can be judged. However, these cues can also be misleading. In the rod-and-frame illusion, for example, a large tilted frame distorts the observerʼs sense of vertical, caus- ing an enclosed rod to appear tilted in the opposite direction. To determine the brain region responsible for processing these spatial cues, we used TMS to suppress neural activity in the superior parietal lobule of healthy observers. Stimulation of the right hemisphere, but not the left, caused a significant reduc- tion in rod-and-frame susceptibility. In contrast, a tilt illusion caused by a mechanism that does not involve a distortion of the observerʼs egocentric reference frame was unaffected. These results demonstrate that the right superior parietal lobule is actively involved in processing the contextual cues that contribute to our perception of egocentric space. |
Indra T. Mahayana; Chia-Lun Liu; Chi Fu Chang; Daisy L. Hung; Ovid J. L. Tzeng; Chi-Hung Juan; Neil G. Muggleton Far-space neglect in conjunction but not feature search following transcranial magnetic stimulation over right posterior parietal cortex Journal Article In: Journal of Neurophysiology, vol. 111, no. 4, pp. 705–714, 2014. @article{Mahayana2014, Near- and far-space coding in the human brain is a dynamic process. Areas in dorsal, as well as ventral visual association cortex, including right posterior parietal cortex (rPPC), right frontal eye field (rFEF), and right ventral occipital cortex (rVO), have been shown to be important in visuospatial processing, but the involvement of these areas when the information is in near or far space remains unclear. There is a need for investigations of these representations to help explain the pathophysiology of hemispatial neglect, and the role of near and far space is crucial to this. We used a conjunction visual search task using an elliptical array to investigate the effects of transcranial magnetic stimulation delivered over rFEF, rPPC, and rVO on the processing of targets in near and far space and at a range of horizontal eccentricities. As in previous studies, we found that rVO was involved in far-space search, and rFEF was involved regardless of the distance to the array. It was found that rPPC was involved in search only in far space, with a neglect-like effect when the target was located in the most eccentric locations. No effects were seen for any site for a feature search task. As the search arrays had higher predictability with respect to target location than is often the case, these data may form a basis for clarifying both the role of PPC in visual search and its contribution to neglect, as well as the importance of near and far space in these. |
Heath Matheson; Aaron J. Newman; Jason Satel; Patricia A. McMullen Handles of manipulable objects attract covert visual attention: ERP evidence Journal Article In: Brain and Cognition, vol. 86, no. 1, pp. 17–23, 2014. @article{Matheson2014, Previous research has demonstrated that people are faster at making a manual response with the hand that is aligned with the handle of a manipulable object compared to its functional end. According to theories of embodied cognition (ETC), the presentation of a manipulable object automatically elicits sensorimotor simulations of the respective hand and these simulations facilitate the response. However, an alternative interpretation of these data is that handles preferentially attract visual attention, since attended stimuli and locations typically elicit faster responses. We investigated attentional biases elicited by manipulable and non-manipulable objects using event-related-potentials (ERPs). On each trial, a picture of a manipulable object was followed by a target dot that participants had to make a button-press to. The dot was located at either the handle or functional end of the object. Consistent with previous attentional cuing paradigms, we showed that the P1 ERP component was greater in response to targets cued by handles than by functional ends. These results suggest that object handles automatically bias covert attentional processes. These attentional biases may account for earlier behavioural findings, without any recourse to ETC. |
Muriel T. N. Panouillères; Ouazna Habchi; Peggy Gerardin; Roméo Salemme; Christian Urquizar; Alessandro Farnè; Denis Pélisson A role for the parietal cortex in sensorimotor adaptation of saccades Journal Article In: Cerebral Cortex, vol. 24, no. 2, pp. 304–314, 2014. @article{Panouilleres2014, Sensorimotor adaptation ensures movement accuracy despite continuously changing environment and body. Adaptation of saccadic eye movements is a classical model of sensorimotor adaptation. Beside the well-established role of the brainstem-cerebellum in the adaptation of reactive saccades (RSs), the cerebral cortex has been suggested to be involved in the adaptation of voluntary saccades (VSs). Here, we provide direct evidence for a causal involvement of the parietal cortex in saccadic adaptation. First, the posterior intraparietal sulcus (pIPS) was identified in each subject using functional magnetic resonance imaging (fMRI). Then, a saccadic adaptation paradigm was used to progressively reduce the amplitude of RSs and VSs, while single-pulse transcranial magnetic stimulation (spTMS) was applied over the right pIPS. The perturbations of pIPS resulted in impairment for the adaptation of VSs, selectively when spTMS was applied 60 ms after saccade onset. In contrast, the adaptation of RSs was facilitated by spTMS applied 90 ms after saccade initiation. The differential effect of spTMS relative to saccade types suggests a direct interference with pIPS activity for the VS adaptation and a remote interference with brainstem-cerebellum activity for the RS adaptation. These results support the hypothesis that the adaptation of VSs and RSs involves different neuronal substrates. |
Cheolsoo Park; Markus Plank; Joseph Snider; Sanggyun Kim; He Crane Huang; Sergei Gepshtein; Todd P. Coleman; Howard Poizner In: IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. 22, no. 5, pp. 1083–1096, 2014. @article{Park2014, The neural dynamics underlying the coordination of spatially-directed limb and eye movements in humans is not well understood. Part of the difficulty has been a lack of signal processing tools suitable for the analysis of non-stationary electroencephalographic (EEG) signals. Here we use multivariate empirical mode decomposition (MEMD), a data-driven approach that does not employ predefined basis functions. High-density EEG, and arm and eye movements were synchronously recorded in 10 subjects performing time-constrained reaching and/or eye movements. Subjects were allowed to move both the hand and the eyes, only the hand, or only the eyes following a 500-700 ms delay interval where the hand and gaze remained on a central fixation cross. An additional condition involved a non-spatially-directed "lift" movement of the hand. The neural activity during a 500 ms delay interval was decomposed into intrinsic mode functions (IMFs) usingMEMD. Classification analysis revealed that gamma band (30 Hz <) IMFs produced more classifiable features differentiating the EEG according to the different upcoming movements. A benchmark test using conventional algorithms demonstrated that MEMD was the best algorithm for extracting oscillatory bands from EEG, yielding the best classification of the different movement conditions. The gamma rhythm decomposed using MEMD showed a higher correlation with the eventual movement accuracy than any other band rhythm and than any other algorithm. |
Hyeong Dong Park; Stéphanie Correia; Antoine Ducorps; Catherine Tallon-Baudry Spontaneous fluctuations in neural responses to heartbeats predict visual detection Journal Article In: Nature Neuroscience, vol. 17, no. 4, pp. 612–618, 2014. @article{Park2014a, Spontaneous fluctuations of ongoing neural activity substantially affect sensory and cognitive performance. Because bodily signals are constantly relayed up to the neocortex, neural responses to bodily signals are likely to shape ongoing activity. Here, using magnetoencephalography, we show that in humans, neural events locked to heartbeats before stimulus onset predict the detection of a faint visual grating in the posterior right inferior parietal lobule and the ventral anterior cingulate cortex, two regions that have multiple functional correlates and that belong to the same resting-state network. Neither fluctuations in measured bodily parameters nor overall cortical excitability could account for this finding. Neural events locked to heartbeats therefore shape visual conscious experience, potentially by contributing to the neural maps of the organism that might underlie subjectivity. Beyond conscious vision, our results show that neural events locked to a basic physiological input such as heartbeats underlie behaviorally relevant differential activation in multifunctional cortical areas. |
Rafael Polanía; Ian Krajbich; Marcus Grueschow; Christian C. Ruff Neural oscillations and synchronization differentially support evidence accumulation in perceptual and value-based decision making Journal Article In: Neuron, vol. 82, no. 3, pp. 709–720, 2014. @article{Polania2014, Organisms make two types of decisions on a regular basis. Perceptual decisions are determined by objective states of the world (e.g., melons are bigger than apples), whereas value-based decisions are determined by subjective preferences (e.g., I prefer apples to melons). Theoretical accounts suggest that both types of choice involve neural computations accumulating evidence for the choice alternatives; however, little is known about the overlap or differences in the processes underlying perceptual versus value-based decisions. We analyzed EEG recordings during a paradigm where perceptual- and value-based choices were based on identical stimuli. For both types of choice, evidence accumulation was evident in parietal gamma-frequency oscillations, whereas a similar frontal signal was unique for value-based decisions. Fronto-parietal synchronization of these signals predicted value-based choice accuracy. These findings uncover how decisions emerge from topographic- and frequency-specificoscillations that accumulate distinct aspects of evidence, with large-scale synchronization as a mechanism integrating these spatially distributed signals. |
Liina Pylkkänen; Douglas K. Bemis; Estibaliz Blanco Elorrieta Building phrases in language production: An MEG study of simple composition Journal Article In: Cognition, vol. 133, no. 2, pp. 371–384, 2014. @article{Pylkkaenen2014, Although research on language production has developed detailed maps of the brain basis of single word production in both time and space, little is known about the spatiotemporal dynamics of the processes that combine individual words into larger representations during production. Studying composition in production is challenging due to difficulties both in controlling produced utterances and in measuring the associated brain responses. Here, we circumvent both problems using a minimal composition paradigm combined with the high temporal resolution of magnetoencephalography (MEG). With MEG, we measured the planning stages of simple adjective-noun phrases ('red tree'), matched list controls ('red, blue'), and individual nouns ('tree') and adjectives ('red'), with results indicating combinatorial processing in the ventro-medial prefrontal cortex (vmPFC) and left anterior temporal lobe (LATL), two regions previously implicated for the comprehension of similar phrases. These effects began relatively quickly (~180 ms) after the presentation of a production prompt, suggesting that combination commences with initial lexical access. Further, while in comprehension, vmPFC effects have followed LATL effects, in this production paradigm vmPFC effects occurred mostly in parallel with LATL effects, suggesting that a late process in comprehension is an early process in production. Thus, our results provide a novel neural bridge between psycholinguistic models of comprehension and production that posit functionally similar combinatorial mechanisms operating in reversed order. |
Lily Riggs; Takako Fujioka; Jessica Chan; Douglas A. McQuiggan; Adam K. Anderson; Jennifer D. Ryan Association with emotional information alters subsequent processing of neutral faces Journal Article In: Frontiers in Human Neuroscience, vol. 8, pp. 1001, 2014. @article{Riggs2014, The processing of emotional as compared to neutral information is associated with different patterns in eye movement and neural activity. However, the 'emotionality' of a stimulus can be conveyed not only by its physical properties, but also by the information that is presented with it. There is very limited work examining the how emotional information may influence the immediate perceptual processing of otherwise neutral information. We examined how presenting an emotion label for a neutral face may influence subsequent processing by using eye movement monitoring (EMM) and magnetoencephalography (MEG) simultaneously. Participants viewed a series of faces with neutral expressions. Each face was followed by a unique negative or neutral sentence to describe that person, and then the same face was presented in isolation again. Viewing of faces paired with a negative sentence was associated with increased early viewing of the eye region and increased neural activity between 600 and 1200 ms in emotion processing regions such as the cingulate, medial prefrontal cortex, and amygdala, as well as posterior regions such as the precuneus and occipital cortex. Viewing of faces paired with a neutral sentence was associated with increased activity in the parahippocampal gyrus during the same time window. By monitoring behavior and neural activity within the same paradigm, these findings demonstrate that emotional information alters subsequent visual scanning and the neural systems that are presumably invoked to maintain a representation of the neutral information along with its emotional details. |
Lillian M. Rigoli; Daniel Holman; Michael J. Spivey; Christopher T. Kello In: Frontiers in Human Neuroscience, vol. 8, pp. 713, 2014. @article{Rigoli2014, When humans perform a response task or timing task repeatedly, fluctuations in measures of timing from one action to the next exhibit long-range correlations known as 1/f noise. The origins of 1/f noise in timing have been debated for over 20 years, with one common explanation serving as a default: humans are composed of physiological processes throughout the brain and body that operate over a wide range of timescales, and these processes combine to be expressed as a general source of 1/f noise. To test this explanation, the present study investigated the coupling vs. independence of 1/f noise in timing deviations, key-press durations, pupil dilations, and heartbeat intervals while tapping to an audiovisual metronome. All four dependent measures exhibited clear 1/f noise, regardless of whether tapping was synchronized or syncopated. 1/f spectra for timing deviations were found to match those for key-press durations on an individual basis, and 1/f spectra for pupil dilations matched those in heartbeat intervals. Results indicate a complex, multiscale relationship among 1/f noises arising from common sources, such as those arising from timing functions vs. those arising from autonomic nervous system (ANS) functions. Results also provide further evidence against the default hypothesis that 1/f noise in human timing is just the additive combination of processes throughout the brain and body. Our findings are better accommodated by theories of complexity matching that begin to formalize multiscale coordination as a foundation of human behavior. |
Carlos M. Hamamé; Juan R. Vidal; Marcela Perrone-Bertolotti; Tomás Ossandón; Karim Jerbi; Philippe Kahane; Olivier Bertrand; Jean Philippe Lachaux Functional selectivity in the human occipitotemporal cortex during natural vision: Evidence from combined intracranial EEG and eye-tracking Journal Article In: NeuroImage, vol. 95, pp. 276–286, 2014. @article{Hamame2014, Eye movements are a constant and essential component of natural vision, yet, most of our knowledge about the human visual system comes from experiments that restrict them. This experimental constraint is mostly in place to control visual stimuli presentation and to avoid artifacts in non-invasive measures of brain activity, however, this limitation can be overcome with intracranial EEG (iEEG) recorded from epilepsy patients. Moreover, the high-frequency components of the iEEG signal (between about 50 and 150. Hz) can provide a proxy of population-level spiking activity in any cortical area during free-viewing. We combined iEEG with high precision eye-tracking to study fine temporal dynamics and functional specificity in the fusiform face (FFA) and visual word form area (VWFA) while patients inspected natural pictures containing faces and text. We defined the first local measure of visual (electrophysiological) responsiveness adapted to free-viewing in humans: amplitude modulations in the high-frequency activity range (50-150. Hz) following fixations (fixation-related high-frequency response). We showed that despite the large size of receptive fields in the ventral occipito-temporal cortex, neural activity during natural vision of realistic cluttered scenes is mostly dependent upon the category of the foveated stimulus - suggesting that category-specificity is preserved during free-viewing and that attention mechanisms might filter out the influence of objects surrounding the fovea. |
Wei He; Jon Brock; Blake W. Johnson Face-sensitive brain responses measured from a four-year-old child with a custom-sized child MEG system Journal Article In: Journal of Neuroscience Methods, vol. 222, pp. 213–217, 2014. @article{He2014, Background: Previous magnetoencephalography (MEG) studies have failed to find a facesensitive, brain response-M170 in children. If this is the case, this suggests that the developmental trajectory of the M170 is different from that of its electrical equivalent, the N170. We investigated the alternative possibility that the child M170 may not be detectable in conventional adult-sized MEG systems. New method: Brain responses to pictures of faces and well controlled stimuli were measured from the same four-year-old child with a custom child MEG system and an adult-sized MEG system. Results: The goodness of fit of the child's head was about the same over the occipital head surface in both systems, but was much worse over all other parts of the head surface in the adult MEG system compared to the child MEG system. The face-sensitive M170 was measured from the child in both MEG systems, but was larger in amplitude, clearer in morphology, and had a more accurate source localization when measured in the child MEG system. Comparison with existing method: The custom-sized child MEG system is superior for measuring the face-sensitive M170 brain response in children than the conventional adult MEG system. Conclusions: The present results show that the face-sensitive M170 brain response can be elicited in a four-year-old child. This provides new evidence for early maturation of face processing brain mechanisms in humans, and offers new opportunities for the study of neurodevelopmental disorders that show atypical face processing capabilities, such as autism spectrum disorder. |
Randolph F. Helfrich; Hannah Knepper; Guido Nolte; Daniel Strüber; Stefan Rach; Christoph S. Herrmann; Till R. Schneider; Andreas K. Engel Selective modulation of interhemispheric functional connectivity by HD-tACS shapes perception Journal Article In: PLoS Biology, vol. 12, no. 12, pp. 1–15, 2014. @article{Helfrich2014, Oscillatory neuronal synchronization between cortical areas has been suggested to constitute a flexible mechanism to coordinate information flow in the human cerebral cortex. However, it remains unclear whether synchronized neuronal activity merely represents an epiphenomenon or whether it is causally involved in the selective gating of information. Here, we combined bilateral high-density transcranial alternating current stimulation (HD-tACS) at 40 Hz with simultaneous electroencephalographic (EEG) recordings to study immediate electrophysiological effects during the selective entrainment of oscillatory gamma-band signatures. We found that interhemispheric functional connectivity was modulated in a predictable, phase-specific way: In-phase stimulation enhanced synchronization, anti-phase stimulation impaired functional coupling. Perceptual correlates of these connectivity changes were found in an ambiguous motion task, which strongly support the functional relevance of long-range neuronal coupling. Additionally, our results revealed a decrease in oscillatory alpha power in response to the entrainment of gamma band signatures. This finding provides causal evidence for the antagonistic role of alpha and gamma oscillations in the parieto-occipital cortex and confirms that the observed gamma band modulations were physiological in nature. Our results demonstrate that synchronized cortical network activity across several spatiotemporal scales is essential for conscious perception and cognition. |
Kasey S. Hemington; James N. Reynolds In: Clinical Neurophysiology, vol. 125, no. 12, pp. 2364–2371, 2014. @article{Hemington2014, Objective: Children with Fetal Alcohol Spectrum Disorder (FASD) exhibit cognitive deficits that can be probed using eye movement tasks. We employed a recently developed, single-sensor electroencephalographic (EEG) recording device in measuring EEG activity during the performance of an eye movement task probing working memory in this population. Methods: Children with FASD (n= 18) and typically developing children (n= 19) performed a memory-guided saccade task requiring the participant to remember the spatial location of one, two or three stimuli. We hypothesized that children with FASD would (i) exhibit performance deficits, particularly at greater mnemonic loads; and (ii) display differences in theta (4-8 Hz) and alpha (8-12 Hz) frequency band power compared with controls. Results: Children with FASD failed to perform the task correctly more often than controls when presented with two or three stimuli, and demonstrated related reductions in alpha and theta power. Conclusion: These data suggest that the memory-guided task is sensitive to working memory deficits in children with FASD. Significance: Simultaneous recording of EEG activity suggest differing patterns of underlying neural recruitment in the clinical group, consistent with previous literature indicating more cognitive resources are required by children with FASD in order to complete complex tasks correctly. |
Linbi Hong; Jennifer M. Walz; Paul Sajda Your eyes give you away: Prestimulus changes in pupil diameter correlate with poststimulus task-related EEG dynamics Journal Article In: PLoS ONE, vol. 9, no. 3, pp. e91321, 2014. @article{Hong2014, Pupillary measures have been linked to arousal and attention as well as activity in the brainstem's locus coeruleus norepinephrine (LC-NE) system. Similarly, there is evidence that evoked EEG responses, such as the P3, might have LC-NE activity as their basis. Since it is not feasible to record electrophysiological data directly from the LC in humans due to its location in the brainstem, an open question has been whether pupillary measures and EEG variability can be linked in a meaningful way to shed light on the nature of the LC-NE role in attention and arousal. We used an auditory oddball task with a data-driven approach to learn task-relevant projections of the EEG, for windows of data spanning the entire trial. We investigated linear and quadratic relationships between the evoked EEG along these projections and both prestimulus (baseline) and poststimulus (evoked dilation) pupil diameter measurements. We found that baseline pupil diameter correlates with early (175-200 ms) and late (350-400 ms) EEG component variability, suggesting a linear relationship between baseline (tonic) LC-NE activity and evoked EEG. We found no relationships between evoked EEG and evoked pupil dilation, which is often associated with evoked (phasic) LC activity. After regressing out reaction time (RT), the correlation between EEG variability and baseline pupil diameter remained, suggesting that such correlation is not explainable by RT variability. We also investigated the relationship between these pupil measures and prestimulus EEG alpha activity, which has been reported as a marker of attentional state, and found a negative linear relationship with evoked pupil dilation. In summary, our results demonstrate significant relationships between prestimulus and poststimulus neural and pupillary measures, and they provide further evidence for tight coupling between attentional state and evoked neural activity and for the role of cortical and subcortical networks underlying the process of target detection. |
Jörn M. Horschig; Ole Jensen; Martine R. Schouwenburg; Roshan Cools; Mathilde Bonnefond Alpha activity reflects individual abilities to adapt to the environment Journal Article In: NeuroImage, vol. 89, pp. 235–243, 2014. @article{Horschig2014, Recent findings suggest that oscillatory alpha activity (7-13. Hz) is associated with functional inhibition of sensory regions by filtering incoming information. Accordingly the alpha power in visual regions varies in anticipation of upcoming, predictable stimuli which has consequences for visual processing and subsequent behavior. In covert spatial attention studies it has been demonstrated that performance correlates with the adaptation of alpha power in response to explicit spatial cueing. However it remains unknown whether such an adaptation also occurs in response to implicit statistical properties of a task. In a covert attention switching paradigm, we here show evidence that individuals differ on how they adapt to implicit statistical properties of the task. Subjects whose behavioral performance reflects the implicit change in switch trial likelihood show strong adjustment of anticipatory alpha power lateralization. Most importantly, the stronger the behavioral adjustment to the switch trial likelihood was, the stronger the adjustment of anticipatory posterior alpha lateralization. We conclude that anticipatory spatial attention is reflected in the distribution of posterior alpha band power which is predictive of individual detection performance in response to the implicit statistical properties of the task. |
Leyla Isik; Ethan M. Meyers; Joel Z. Leibo; Tomaso Poggio The dynamics of invariant object recognition in the human visual system Journal Article In: Journal of Neurophysiology, vol. 111, no. 1, pp. 91–102, 2014. @article{Isik2014, The human visual system can rapidly recognize objects despite transformations that alter their appearance. The precise timing of when the brain computes neural representations that are invariant to particular transformations, however, has not been mapped in humans. Here we employ magnetoencephalography decoding analysis to measure the dynamics of size- and position-invariant visual information development in the ventral visual stream. With this method we can read out the identity of objects beginning as early as 60 ms. Size- and position-invariant visual information appear around 125 ms and 150 ms, respectively, and both develop in stages, with invariance to smaller transformations arising before invariance to larger transformations. Additionally, the magnetoencephalography sensor activity localizes to neural sources that are in the most posterior occipital regions at the early decoding times and then move temporally as invariant information develops. These results provide previously unknown latencies for key stages of human-invariant object recognition, as well as new and compelling evidence for a feed-forward hierarchical model of invariant object recognition where invariance increases at each successive visual area along the ventral stream. |
David C. Jangraw; Jun Wang; Brent J. Lance; Shih Fu Chang; Paul Sajda Neurally and ocularly informed graph-based models for searching 3D environments Journal Article In: Journal of Neural Engineering, vol. 11, no. 4, pp. 1–13, 2014. @article{Jangraw2014a, OBJECTIVE: As we move through an environment, we are constantly making assessments, judgments and decisions about the things we encounter. Some are acted upon immediately, but many more become mental notes or fleeting impressions-our implicit 'labeling' of the world. In this paper, we use physiological correlates of this labeling to construct a hybrid brain-computer interface (hBCI) system for efficient navigation of a 3D environment. APPROACH: First, we record electroencephalographic (EEG), saccadic and pupillary data from subjects as they move through a small part of a 3D virtual city under free-viewing conditions. Using machine learning, we integrate the neural and ocular signals evoked by the objects they encounter to infer which ones are of subjective interest to them. These inferred labels are propagated through a large computer vision graph of objects in the city, using semi-supervised learning to identify other, unseen objects that are visually similar to the labeled ones. Finally, the system plots an efficient route to help the subjects visit the 'similar' objects it identifies. MAIN RESULTS: We show that by exploiting the subjects' implicit labeling to find objects of interest instead of exploring naively, the median search precision is increased from 25% to 97%, and the median subject need only travel 40% of the distance to see 84% of the objects of interest. We also find that the neural and ocular signals contribute in a complementary fashion to the classifiers' inference of subjects' implicit labeling. SIGNIFICANCE: In summary, we show that neural and ocular signals reflecting subjective assessment of objects in a 3D environment can be used to inform a graph-based learning model of that environment, resulting in an hBCI system that improves navigation and information delivery specific to the user's interests. |
Marc R. Kamke; Alexander E. Ryan; Martin V. Sale; Megan E. J. Campbell; Stephan Riek; Timothy J. Carroll; Jason B. Mattingley Visual spatial attention has opposite effects on bidirectional plasticity in the human motor cortex Journal Article In: Journal of Neuroscience, vol. 34, no. 4, pp. 1475–1480, 2014. @article{Kamke2014, Long-term potentiation (LTP) and long-term depression (LTD) are key mechanisms of synaptic plasticity that are thought to act in concert to shape neural connections. Here we investigated the influence of visual spatial attention on LTP-like and LTD-like plasticity in the human motor cortex. Plasticity was induced using paired associative stimulation (PAS), which involves repeated pairing of peripheral nerve stimulation and transcranial magnetic stimulation to alter functional responses in the thumb area of the primary motor cortex. PAS-induced changes in cortical excitability were assessed using motor-evoked potentials. During plasticity induction, participants directed their attention to one of two visual stimulus streams located adjacent to each hand. When participants attended to visual stimuli located near the left thumb, which was targeted by PAS, LTP-like increases in excitability were significantly enhanced, and LTD-like decreases in excitability reduced, relative to when they attended instead to stimuli located near the right thumb. These differential effects on (bidirectional) LTP-like and LTD-like plasticity suggest that voluntary visual attention can exert an important influence on the functional organization of the motor cortex. Specifically, attention acts to both enhance the strengthening and suppress the weakening of neural connections representing events that fall within the focus of attention. |
Min Suk Kang; Geoffrey F. Woodman The neurophysiological index of visual working memory maintenance is not due to load dependent eye movements Journal Article In: Neuropsychologia, vol. 56, no. 1, pp. 63–72, 2014. @article{Kang2014, The Contralateral Delayed Activity (CDA) is slow negative potential found during a variety of tasks, providing an important measure of the representation of information in visual working memory. However, it is studied using stimulus arrays in which the to-be-remembered objects are shown in the periphery of the left or the right visual field. Our goal was to determine whether fixational eye movements in the direction of the memoranda might underlie the CDA. We found that subjects' gaze was shifted toward the visual field of the memoranda during the retention interval, with its magnitude increasing with the set size. However, the CDA was clearly observed even when the subjects' gaze shifts were absent. In addition, the magnitude of the subjects' gaze shifts was unrelated to their visual working memory capacity measured with behavioral data, unlike the CDA. Finally, the onset latency of the set size dependent eye movements followed the onset of the set size dependent CDA. Thus, our findings clearly show that the CDA does not represent a simple inability to maintain fixation during visual working memory maintenance, but that this neural index of representation in working memory appears to induce eye movements toward the locations of the objects being remembered. |
Kohitij Kar; Bart Krekelberg Transcranial alternating current stimulation attenuates visual motion adaptation Journal Article In: Journal of Neuroscience, vol. 34, no. 21, pp. 7334–7340, 2014. @article{Kar2014, Transcranial alternating current stimulation (tACS) is used in clinical applications and basic neuroscience research. Although its behavioral effects are evident from prior reports, current understanding of the mechanisms that underlie these effects is limited. We used motion perception, a percept with relatively well known properties and underlying neural mechanisms to investigate tACS mechanisms. Healthy human volunteers showed a surprising improvement in motion sensitivity when visual stimuli were paired with 10 Hz tACS. In addition, tACS reduced the motion-after effect, and this reduction was correlated with the improvement in motion sensitivity. Electrical stimulation had no consistent effect when applied before presenting a visual stimulus or during recovery from motion adaptation. Together, these findings suggest that perceptual effects of tACS result from an attenuation of adaptation. Important consequences for the practical use of tACS follow from our work. First, because this mechanism interferes only with adaptation, this suggests that tACS can be targeted at subsets of neurons (by adapting them), even when the applied currents spread widely throughout the brain. Second, by interfering with adaptation, this mechanism provides a means by which electrical stimulation can generate behavioral effects that outlast the stimulation. |
Lisandro N. Kaunitz; Juan E. Kamienkowski; Alexander Varatharajah; Mariano Sigman; Rodrigo Quian Quiroga; Matias J. Ison Looking for a face in the crowd: Fixation-related potentials in an eye-movement visual search task Journal Article In: NeuroImage, vol. 89, pp. 297–305, 2014. @article{Kaunitz2014, Despite the compelling contribution of the study of event related potentials (ERPs) and eye movements to cognitive neuroscience, these two approaches have largely evolved independently. We designed an eye-movement visual search paradigm that allowed us to concurrently record EEG and eye movements while subjects were asked to find a hidden target face in a crowded scene with distractor faces. Fixation event-related potentials (fERPs) to target and distractor stimuli showed the emergence of robust sensory components associated with the perception of stimuli and cognitive components associated with the detection of target faces. We compared those components with the ones obtained in a control task at fixation: qualitative similarities as well as differences in terms of scalp topography and latency emerged between the two. By using single trial analyses, fixations to target and distractors could be decoded from the EEG signals above chance level in 11 out of 12 subjects. Our results show that EEG signatures related to cognitive behavior develop across spatially unconstrained exploration of natural scenes and provide a first step towards understanding the mechanisms of target detection during natural search. |
Christof Körner; Verena Braunstein; Matthias Stangl; Alois Schlögl; Christa Neuper; Anja Ischebeck In: Psychophysiology, vol. 51, no. 4, pp. 385–395, 2014. @article{Koerner2014, To search for a target in a complex environment is an everyday behavior that ends with finding the target. When we search for two identical targets, however, we must continue the search after finding the first target and memorize its location. We used fixation-related potentials to investigate the neural correlates of different stages of the search, that is, before and after finding the first target. Having found the first target influenced subsequent distractor processing. Compared to distractor fixations before the first target fixation, a negative shift was observed for three subsequent distractor fixations. These results suggest that processing a target in continued search modulates the brain's response, either transiently by reflecting temporary working memory processes or permanently by reflecting working memory retention. |
2013 |
M. Guitart-Masip; G. R. Barnes; A. Horner; Markus Bauer; Raymond J. Dolan; E. Duzel Synchronization of medial temporal lobe and prefrontal rhythms in human decision making Journal Article In: Journal of Neuroscience, vol. 33, no. 2, pp. 442–451, 2013. @article{GuitartMasip2013, Optimal decision making requires that we integrate mnemonic information regarding previous decisions with value signals that entail likely rewards and punishments. The fact that memory and value signals appear to be coded by segregated brain regions, the hippocampus in the case of memory and sectors of prefrontal cortex in the case of value, raises the question as to how they are integrated during human decision making. Using magnetoencephalography to study healthy human participants, we show increased theta oscillations over frontal and temporal sensors during nonspatial decisions based on memories from previous trials. Using source reconstruction we found that the medial temporal lobe (MTL), in a location compatible with the anterior hippocampus, and the anterior cingulate cortex in the medial wall of the frontal lobe are the source of this increased theta power. Moreover, we observed a correlation between theta power in the MTL source and behavioral performance in decision making, supporting a role for MTL theta oscillations in decision-making performance. These MTL theta oscillations were synchronized with several prefrontal sources, including lateral superior frontal gyrus, dorsal anterior cingulate gyrus, and medial frontopolar cortex. There was no relationship between the strength of synchronization and the expected value of choices. Our results indicate a mnemonic guidance of human decision making, beyond anticipation of expected reward, is supported by hippocampal-prefrontal theta synchronization. |
Uwe Hassler; Uwe Friese; Ulla Martens; Nelson Trujillo-Barreto; Thomas Gruber Repetition priming effects dissociate between miniature eye movements and induced gamma-band responses in the human electroencephalogram Journal Article In: European Journal of Neuroscience, vol. 38, no. 3, pp. 2425–2433, 2013. @article{Hassler2013, The role of induced gamma-band responses (iGBRs) in the human electroencephalogram (EEG) is a controversial topic. On the one hand, iGBRs have been associated with neuronal activity reflecting the (re-)activation of cortical object representations. On the other hand, it was shown that miniature saccades (MSs) lead to high-frequency artifacts in the EEG that can mimic cortical iGBRs. We recorded EEG and eye movements simultaneously while participants were engaged in a combined repetition priming and object recognition experiment. MS rates were mainly modulated by object familiarity in a time window from 100 to 300 ms after stimulus onset. In contrast, artifact-corrected iGBRs were sensitive to object repetition and object familiarity in a prolonged time window. EEG source analyses revealed that stimulus repetitions modulated iGBRs in temporal and occipital cortex regions while familiarity was associated with activity in parieto-occipital regions. These results are in line with neuroimaging studies employing functional magnetic resonance imaging or magnetoencephalography. We conclude that MSs reflect early mechanisms of visual perception while iGBRs mirror the activation of cortical networks representing a perceived object. |
John M. Henderson; Steven G. Luke; Joseph Schmidt; John E. Richards Co-registration of eye movements and event-related potentials in connected-text paragraph reading Journal Article In: Frontiers in Systems Neuroscience, vol. 7, pp. 28, 2013. @article{Henderson2013, Eyetracking during reading has provided a critical source of on-line behavioral data informing basic theory in language processing. Similarly, event-related potentials (ERPs) have provided an important on-line measure of the neural correlates of language processing. Recently there has been strong interest in co-registering eyetracking and ERPs from simultaneous recording to capitalize on the strengths of both techniques, but a challenge has been devising approaches for controlling artifacts produced by eye movements in the EEG waveform. In this paper we describe our approach to correcting for eye movements in EEG and demonstrate its applicability to reading. The method is based on independent components analysis, and uses three criteria for identifying components tied to saccades: (1) component loadings on the surface of the head are consistent with eye movements; (2) source analysis localizes component activity to the eyes, and (3) the temporal activation of the component occurred at the time of the eye movement and differed for right and left eye movements. We demonstrate this method's applicability to reading by comparing ERPs time-locked to fixation onset in two reading conditions. In the text-reading condition, participants read paragraphs of text. In the pseudo-reading control condition, participants moved their eyes through spatially similar pseudo-text that preserved word locations, word shapes, and paragraph spatial structure, but eliminated meaning. The corrected EEG, time-locked to fixation onsets, showed effects of reading condition in early ERP components. The results indicate that co-registration of eyetracking and EEG in connected-text paragraph reading is possible, and has the potential to become an important tool for investigating the cognitive and neural bases of on-line language processing in reading. |
Florian Hutzler; Isabella Fuchs; Benjamin Gagl; Sarah Schuster; Fabio Richlan; Mario Braun; Stefan Hawelka Parafoveal X-masks interfere with foveal word recognition: Evidence from fixation-related brain potentials Journal Article In: Frontiers in Systems Neuroscience, vol. 7, pp. 33, 2013. @article{Hutzler2013, The boundary paradigm, in combination with parafoveal masks, is the main technique for studying parafoveal preprocessing during reading. The rationale is that the masks (e.g., strings of X's) prevent parafoveal preprocessing, but do not interfere with foveal processing. A recent study, however, raised doubts about the neutrality of parafoveal masks. In the present study, we explored this issue by means of fixation-related brain potentials (FRPs). Two FRP conditions presented rows of five words. The task of the participant was to judge whether the final word of a list was a "new" word, or whether it was a repeated (i.e., "old") word. The critical manipulation was that the final word was X-masked during parafoveal preview in one condition, whereas another condition presented a valid preview of the word. In two additional event-related brain potential (ERP) conditions, the words were presented serially with no parafoveal preview available; in one of the conditions with a fixed timing, in the other word presentation was self-paced by the participants. Expectedly, the valid-preview FRP condition elicited the shortest processing times. Processing times did not differ between the two ERP conditions indicating that "cognitive readiness" during self-paced processing can be ruled out as an alternative explanation for differences in processing times between the ERP and the FRP conditions. The longest processing times were found in the X-mask FRP condition indicating that parafoveal X-masks interfere with foveal word recognition. |
Maciej Kosilo; Sophie M. Wuerger; Matt Craddock; Ben J. Jennings; Amelia R. Hunt; Jasna Martinovic Low-level and high-level modulations of fixational saccades and high frequency oscillatory brain activity in a visual object classification task Journal Article In: Frontiers in Psychology, vol. 4, pp. 948, 2013. @article{Kosilo2013, Until recently induced gamma-band activity (GBA) was considered a neural marker of cortical object representation. However, induced GBA in the electroencephalogram (EEG) is susceptible to artifacts caused by miniature fixational saccades. Recent studies have demonstrated that fixational saccades also reflect high-level representational processes. Do high-level as opposed to low-level factors influence fixational saccades? What is the effect of these factors on artifact-free GBA? To investigate this, we conducted separate eye tracking and EEG experiments using identical designs. Participants classified line drawings as objects or non-objects. To introduce low-level differences, contours were defined along different directions in cardinal color space: S-cone-isolating, intermediate isoluminant, or a full-color stimulus, the latter containing an additional achromatic component. Prior to the classification task, object discrimination thresholds were measured and stimuli were scaled to matching suprathreshold levels for each participant. In both experiments, behavioral performance was best for full-color stimuli and worst for S-cone isolating stimuli. Saccade rates 200-700 ms after stimulus onset were modulated independently by low and high-level factors, being higher for full-color stimuli than for S-cone isolating stimuli and higher for objects. Low-amplitude evoked GBA and total GBA were observed in very few conditions, showing that paradigms with isoluminant stimuli may not be ideal for eliciting such responses. We conclude that cortical loops involved in the processing of objects are preferentially excited by stimuli that contain achromatic information. Their activation can lead to relatively early exploratory eye movements even for foveally-presented stimuli. |
Franziska Kretzschmar; Dominique Pleimling; Jana Hosemann; Stephan Füssel; Ina Bornkessel-Schlesewsky; Matthias Schlesewsky Subjective impressions do not mirror online reading effort: Concurrent EEG-eyetracking evidence from the reading of books and digital media Journal Article In: PLoS ONE, vol. 8, no. 2, pp. e56178, 2013. @article{Kretzschmar2013, In the rapidly changing circumstances of our increasingly digital world, reading is also becoming an increasingly digital experience: electronic books (e-books) are now outselling print books in the United States and the United Kingdom. Nevertheless, many readers still view e-books as less readable than print books. The present study thus used combined EEG and eyetracking measures in order to test whether reading from digital media requires higher cognitive effort than reading conventional books. Young and elderly adults read short texts on three different reading devices: a paper page, an e-reader and a tablet computer and answered comprehension questions about them while their eye movements and EEG were recorded. The results of a debriefing questionnaire replicated previous findings in that participants overwhelmingly chose the paper page over the two electronic devices as their preferred reading medium. Online measures, by contrast, showed shorter mean fixation durations and lower EEG theta band voltage density–known to covary with memory encoding and retrieval–for the older adults when reading from a tablet computer in comparison to the other two devices. Young adults showed comparable fixation durations and theta activity for all three devices. Comprehension accuracy did not differ across the three media for either group. We argue that these results can be explained in terms of the better text discriminability (higher contrast) produced by the backlit display of the tablet computer. Contrast sensitivity decreases with age and degraded contrast conditions lead to longer reading times, thus supporting the conclusion that older readers may benefit particularly from the enhanced contrast of the tablet. Our findings thus indicate that people's subjective evaluation of digital reading media must be dissociated from the cognitive and neural effort expended in online information processing while reading from such devices. |
Almudena Capilla; Pascal Belin; Joachim Gross The early spatio-temporal correlates and task independence of cerebral voice processing studied with MEG Journal Article In: Cerebral Cortex, vol. 23, no. 6, pp. 1388–1395, 2013. @article{Capilla2013, Functional magnetic resonance imaging studies have repeatedly provided evidence for temporal voice areas (TVAs) with particular sensitivity to human voices along bilateral mid/anterior superior temporal sulci and superior temporal gyri (STS/STG). In contrast, electrophysiological studies of the spatio-temporal correlates of cerebral voice processing have yielded contradictory results, finding the earliest correlates either at ∼300-400 ms, or earlier at ∼200 ms ("fronto-temporal positivity to voice", FTPV). These contradictory results are likely the consequence of different stimulus sets and attentional demands. Here, we recorded magnetoencephalography activity while participants listened to diverse types of vocal and non-vocal sounds and performed different tasks varying in attentional demands. Our results confirm the existence of an early voice-preferential magnetic response (FTPVm, the magnetic counterpart of the FTPV) peaking at about 220 ms and distinguishing between vocal and non-vocal sounds as early as 150 ms after stimulus onset. The sources underlying the FTPVm were localized along bilateral mid-STS/STG, largely overlapping with the TVAs. The FTPVm was consistently observed across different stimulus subcategories, including speech and non-speech vocal sounds, and across different tasks. These results demonstrate the early, largely automatic recruitment of focal, voice-selective cerebral mechanisms with a time-course comparable to that of face processing. |
Brian A. Coffman; Piyadasa Kodituwakku; Elizabeth L. Kodituwakku; Lucinda Romero; Nirupama Muniswamy Sharadamma; David Stone; Julia M. Stephen Primary visual response (M100) delays in adolescents with FASD as measured with MEG Journal Article In: Human Brain Mapping, vol. 34, no. 11, pp. 2852–2862, 2013. @article{Coffman2013, Fetal alcohol spectrum disorders (FASD) are debilitating, with effects of prenatal alcohol exposure persisting into adolescence and adulthood. Complete characterization of FASD is crucial for the development of diagnostic tools and intervention techniques to decrease the high cost to individual families and society of this disorder. In this experiment, we investigated visual system deficits in adolescents (12-21 years) diagnosed with an FASD by measuring the latency of patients' primary visual M100 responses using MEG. We hypothesized that patients with FASD would demonstrate delayed primary visual responses compared to controls. M100 latencies were assessed both for FASD patients and age-matched healthy controls for stimuli presented at the fovea (central stimulus) and at the periphery (peripheral stimuli; left or right of the central stimulus) in a saccade task requiring participants to direct their attention and gaze to these stimuli. Source modeling was performed on visual responses to the central and peripheral stimuli and the latency of the first prominent peak (M100) in the occipital source timecourse was identified. The peak latency of the M100 responses were delayed in FASD patients for both stimulus types (central and peripheral), but the difference in latency of primary visual responses to central vs. peripheral stimuli was significant only in FASD patients, indicating that, while FASD patients' visual systems are impaired in general, this impairment is more pronounced in the periphery. These results suggest that basic sensory deficits in this population may contribute to sensorimotor integration deficits described previously in this disorder. |
Ido Davidesco; Michal Harel; Michal Ramot; Uri Kramer; Svetlana Kipervasser; Fani Andelman; Miri Y. Neufeld; Gadi Goelman; Itzhak Fried; Rafael Malach Spatial and object-based attention modulates broadband high-frequency responses across the human visual cortical hierarchy Journal Article In: Journal of Neuroscience, vol. 33, no. 3, pp. 1228–1240, 2013. @article{Davidesco2013, One of the puzzling aspects in the visual attention literature is the discrepancy between electrophysiological and fMRI findings: whereas fMRI studies reveal strong attentional modulation in the earliest visual areas, single-unit and local field potential studies yielded mixed results. In addition, it is not clear to what extent spatial attention effects extend from early to high-order visual areas. Here we addressed these issues using electrocorticography recordings in epileptic patients. The patients performed a task that allowed simultaneous manipulation ofboth spatial and object-based attention. They were presented with composite stimuli, consisting ofa small object (face or house) superimposed on a large one, and in separate blocks, were instructed to attend one ofthe objects. We found a consistent increase in broadband high-frequency (30–90Hz) power, but not in visual evoked potentials, associated with spatial attention starting withV1/V2 and continuing throughout the visual hierarchy. The magnitude ofthe attentional modulation was correlated with the spatial selectivity of each electrode and its distance from the occipital pole. Interestingly, the latency of the attentional modulation showed a significant decrease along the visual hierarchy. In addition, electrodes placed over high-order visual areas (e.g., fusiform gyrus) showed both effects of spatial and object-based attention. Overall, our results help to reconcile previous observations of discrepancy between fMRI and electrophysiology. They also imply that spatial attention effects can be found both in early and high-order visual cortical areas, in parallel with their stimulus tuning properties. |
Joost C. Dessing; Michael Vesia; J. Douglas Crawford The role of areas MT+/V5 and SPOC in spatial and temporal control of manual interception: An rTMS study Journal Article In: Frontiers in Behavioral Neuroscience, vol. 7, pp. 15, 2013. @article{Dessing2013, Manual interception, such as catching or hitting an approaching ball, requires the hand to contact a moving object at the right location and at the right time. Many studies have examined the neural mechanisms underlying the spatial aspects of goal-directed reaching, but the neural basis of the spatial and temporal aspects of manual interception are largely unknown. Here, we used repetitive transcranial magnetic stimulation (rTMS) to investigate the role of the human middle temporal visual motion area (MT+/V5) and superior parieto-occipital cortex (SPOC) in the spatial and temporal control of manual interception. Participants were required to reach-to-intercept a downward moving visual target that followed an unpredictably curved trajectory, presented on a screen in the vertical plane. We found that rTMS to MT+/V5 influenced interceptive timing and positioning, whereas rTMS to SPOC only tended to increase the spatial variance in reach end points for selected target trajectories. These findings are consistent with theories arguing that distinct neural mechanisms contribute to spatial, temporal, and spatiotemporal control of manual interception. |
Joao C. Dias; Paul Sajda; J. P. Dmochowski; Lucas C. Parra EEG precursors of detected and missed targets during free-viewing search Journal Article In: Journal of Vision, vol. 13, no. 13, pp. 1–19, 2013. @article{Dias2013, When scanning a scene, the target of our search may be in plain sight and yet remain unperceived. Conversely, at other times the target may be perceived in the periphery prior to fixation. There is ample behavioral and neurophysiological evidence to suggest that in some constrained visual-search tasks, targets are detected prior to fixational eye movements. However, limited human data are available during unconstrained search to determine the time course of detection, the brain areas involved, and the neural correlates of failures to detect a foveated target. Here, we recorded and analyzed electroencephalographic (EEG) activity during free-viewing visual search, varying the task difficulty to compare neural signatures for detected and unreported ("missed") targets. When carefully controlled to remove eye-movement-related potentials, saccade-locked EEG shows that: (a) "Easy" targets may be detected as early as 150 ms prior to foveation, as indicated by a premotor potential associated with a button response; (b) object-discriminating occipital activity emerges during the saccade to target; and (c) success and failures to detect a target are accompanied by a modulation in alpha-band power over fronto-central areas as well as altered saccade dynamics. Taken together, these data suggest that target detection during free viewing can begin prior to and continue during a saccade, with failure or success in reporting a target possibly resulting from inhibition or activation of fronto-central processing areas associated with saccade control. |
Ian C. Fiebelkorn; Adam C. Snyder; Manuel R. Mercier; John S. Butler; S. Molholm; John J. Foxe Cortical cross-frequency coupling predicts perceptual outcomes Journal Article In: NeuroImage, vol. 69, pp. 126–137, 2013. @article{Fiebelkorn2013, Functional networks are comprised of neuronal ensembles bound through synchronization across multiple intrinsic oscillatory frequencies. Various coupled interactions between brain oscillators have been described (e.g., phase-amplitude coupling), but with little evidence that these interactions actually influence perceptual sensitivity. Here, electroencephalographic (EEG) recordings were made during a sustained-attention task to demonstrate that cross-frequency coupling has significant consequences for perceptual outcomes (i.e., whether participants detect a near-threshold visual target). The data reveal that phase-detection relationships at higher frequencies are dependent on the phase of lower frequencies, such that higher frequencies alternate between periods when their phase is either strongly or weakly predictive of visual-target detection. Moreover, the specific higher frequencies and scalp topographies linked to visual-target detection also alternate as a function of lower-frequency phase. Cross-frequency coupling between lower (i.e., delta and theta) and higher frequencies (e.g., low- and high-beta) thus results in dramatic fluctuations of visual-target detection. |
Thomas Fischer; Sven-Thomas Graupner; Boris M. Velichkovsky; Sebastian Pannasch Attentional dynamics during free picture viewing: Evidence from oculomotor behavior and electrocortical activity Journal Article In: Frontiers in Systems Neuroscience, vol. 7, pp. 17, 2013. @article{Fischer2013, Most empirical evidence on attentional control is based on brief presentations of rather abstract stimuli. Results revealed indications for a dynamic interplay between bottom-up and top-down attentional mechanisms. Here we used a more naturalistic task to examine temporal signatures of attentional mechanisms on fine and coarse time scales. Subjects had to inspect digitized copies of 60 paintings, each shown for 40 s. We simultaneously measured oculomotor behavior and electrophysiological correlates of brain activity to compare early and late intervals (1) of inspection time of each picture (picture viewing) and (2) of the full experiment (time on task). For picture viewing, we found an increase in fixation duration and a decrease of saccadic amplitude while these parameters did not change with time on task. Furthermore, early in picture viewing we observed higher spatial and temporal similarity of gaze behavior. Analyzing electrical brain activity revealed changes in three components (C1, N1 and P2) of the eye fixation-related potential (EFRP); during picture viewing; no variation was obtained for the power in the frontal beta- and in the theta activity. Time on task analyses demonstrated no effects on the EFRP amplitudes but an increase of power in the frontal theta and beta band activity. Thus, behavioral and electrophysiological measures similarly show characteristic changes during picture viewing, indicating a shifting balance of its underlying (bottom-up and top-down) attentional mechanisms. Time on task also modulated top-down attention but probably represents a different attentional mechanism. |
Aline Frey; Gelu Ionescu; Benoît Lemaire; Francisco López-Orozco; Thierry Baccino; Anne Guérin-Dugué Decision-making in information seeking on texts: an eye-fixation-related potentials investigation Journal Article In: Frontiers in Systems Neuroscience, vol. 7, pp. 39, 2013. @article{Frey2013, Reading on a web page is known to be not linear and people need to make fast decisions about whether they have to stop or not reading. In such context, reading, and decision-making processes are intertwined and this experiment attempts to separate them through electrophysiological patterns provided by the Eye-Fixation-Related Potentials technique (EFRPs). We conducted an experiment in which EFRPs were recorded while participants read blocks of text that were semantically highly related, moderately related, and unrelated to a given goal. Participants had to decide as fast as possible whether the text was related or not to the semantic goal given at a prior stage. Decision making (stopping information search) may occur when the paragraph is highly related to the goal (positive decision) or when it is unrelated to the goal (negative decision). EFRPs were analyzed on and around typical eye fixations: either on words belonging to the goal (target), subjected to a high rate of positive decisions, or on low frequency unrelated words (incongruent), subjected to a high rate of negative decisions. In both cases, we found EFRPs specific patterns (amplitude peaking between 51 to 120 ms after fixation onset) spreading out on the next words following the goal word and the second fixation after an incongruent word, in parietal and occipital areas. We interpreted these results as delayed late components (P3b and N400), reflecting the decision to stop information searching. Indeed, we show a clear spill-over effect showing that the effect on word N spread out on word N + 1 and N + 2. |
Hans Peter Frey; Sophie Molholm; Edmund C. Lalor; Natalie N. Russo; John J. Foxe Atypical cortical representation of peripheral visual space in children with an autism spectrum disorder Journal Article In: European Journal of Neuroscience, vol. 38, no. 1, pp. 2125–2138, 2013. @article{Frey2013a, A key feature of early visual cortical regions is that they contain discretely organized retinotopic maps. Titration of these maps must occur through experience, and the fidelity of their spatial tuning will depend on the consistency and accuracy of the eye movement system. Anomalies in fixation patterns and the ballistics of eye movements are well documented in autism spectrum disorder (ASD), with off-center fixations a hallmark of the phenotype. We hypothesized that these atypicalities might affect the development of visuo-spatial maps and specifically that peripheral inputs might receive altered processing in ASD. Using high-density recordings of visual evoked potentials (VEPs) and a novel system-identification approach known as VESPA (visual evoked spread spectrum analysis), we assessed sensory responses to centrally and peripherally presented stimuli. Additionally, input luminance was varied to bias responsiveness to the magnocellular system, given previous suggestions of magnocellular-specific deficits in ASD. Participants were 22 ASD children (7-17 years of age) and 31 age- and performance-IQ-matched neurotypical controls. Both VEP and VESPA responses to central presentations were indistinguishable between groups. In contrast, peripheral presentations resulted in significantly greater early VEP and VESPA amplitudes in the ASD cohort. We found no evidence that anomalous enhancement was restricted to magnocellular-biased responses. The extent of peripheral response enhancement was related to the severity of stereotyped behaviors and restricted interests, cardinal symptoms of ASD. The current results point to differential visuo-spatial cortical mapping in ASD, shedding light on the consequences of peculiarities in gaze and stereotyped visual behaviors often reported by clinicians working with this population. |
Jason Satel; Matthew D. Hilchey; Zhiguo Wang; Ross Story; Raymond M. Klein The effects of ignored versus foveated cues upon inhibition of return: An event-related potential study Journal Article In: Attention, Perception, and Psychophysics, vol. 75, no. 1, pp. 29–40, 2013. @article{Satel2013, Taylor and Klein (Journal of Experimental Psychology: Human Perception and Performance 26:1639-1656, 2000) discovered two mutually exclusive "flavors" of inhibition of return (IOR): When the oculomotor system is "actively suppressed," IOR affects input processes (the perception/attention flavor), whereas when the oculomotor system is "engaged," IOR affects output processes (the motor flavor). Studies of brain activity with ignored cues have typically reported that IOR reduces an early sensory event-related potential (ERP) component (i.e., the P1 component) of the brain's response to the target. Since eye movements were discouraged in these experiments, the P1 reduction might be a reflection of the perception/attention flavor of IOR. If, instead of ignoring the cue, participants made a prosaccade to the cue (and then returned to fixation) before responding to the target, the motor flavor of IOR should then be generated. We compared these two conditions while monitoring eye position and recording ERPs to the targets. If the P1 modulation is related to the perceptual/attentional flavor of IOR, we hypothesized that it might be absent when the motoric flavor of IOR was generated by a prosaccade to the cue. Our results demonstrated that target-related P1 reductions and behavioral IOR were similar, and significant, in both conditions. However, P1 modulations were significantly correlated with behavioral IOR only when the oculomotor system was actively suppressed, suggesting that P1 modulations may only affect behaviorally exhibited IOR when the attentional/perceptual flavor of IOR is recruited. |
Steven W. Savage; Douglas D. Potter; Benjamin W. Tatler Does preoccupation impair hazard perception? A simultaneous EEG and eye tracking study Journal Article In: Transportation Research Part F: Traffic Psychology and Behaviour, vol. 17, pp. 52–62, 2013. @article{Savage2013, The aim of this current study was to test the hypothesis that contemplating a recent mobile telephone conversation has a detrimental effect on measures of attentional processing in a driving situation. In this within-subjects design, hazard perception performance was compared between high and no cognitive load conditions (with or without a puzzle to solve). We tested 17 participants, all of whom were required to be in possession of a DVLA approved driving license and had completed the hazard perception portion of the British driving test. A novel dual-task paradigm, which did not require subjects to process or produce verbal information during the primary task, was employed to increase participants' cognitive load. Participants were assessed on three categories of performance measures: behavioural, eye movements and cortical activity between both high and no cognitive load conditions whilst watching 20 clips from a hazard perception test. This study was run in a laboratory of the Psychology Research Wing at the University of Dundee. Behavioural findings from the hazard perception test indicate significantly increased reaction times to hazardous stimuli and significantly increased false alarm rates to non-hazardous stimuli in the high cognitive load condition (when contemplating a previous conversation). Analyses of eye movements indicated significant increases in blink frequencies, higher saccade peak velocities and a significant reduction in the spread of fixations along the horizontal axis. Results from EEG recordings showed a significant increase in frontal and a significant decrease in occipital theta activity within the high load condition. Findings were interpreted within the framework of Corbetta, Patel and Schulmann's (2008) networks model of attention control. Our findings suggest that preoccupation with a recent conversation negatively influences the modulatory effect of the central executive on both the stimulus as well as goal-driven networks of the brain. |
K. M. Sharika; Sebastiaan F. W. Neggers; Tjerk P. Gutteling; Stefan Van der Stigchel; Hendrik Chris Dijkerman; A. Murthy Proactive control of sequential saccades in the human supplementary eye field Journal Article In: Proceedings of the National Academy of Sciences, vol. 110, no. 14, pp. E1311–E1320, 2013. @article{Sharika2013, Our ability to regulate behavior based on past experience has thus far been examined using single movements. However, natural behavior typically involves a sequence of movements. Here, we examined the effect of previous trial type on the concurrent planning of sequential saccades using a unique paradigm. The task consisted of two trial types: no-shift trials, which implicitly encouraged the concurrent preparation of the second saccade in a subsequent trial; and target-shift trials, which implicitly discouraged the same in the next trial. Using the intersaccadic interval as an index of concurrent planning, we found evidence for context-based preparation of sequential saccades. We also used functional MRI-guided, single-pulse, transcranial magnetic stimulation on human subjects to test the role of the supplementary eye field (SEF) in the proactive control of sequential eye movements. Results showed that (i) stimulating the SEF in the previous trial disrupted the previous trial type-based preparation of the second saccade in the nonstimulated current trial, (ii) stimulating the SEF in the current trial rectified the disruptive effect caused by stimulation in the previous trial, and (iii) stimulating the SEF facilitated the preparation of second saccades based on previous trial type even when the previous trial was not stimulated. Taken together, we show how the human SEF is causally involved in proactive preparation of sequential saccades. |
Yoshihito Shigihara; Semir Zeki Parallelism in the brain's visual form system Journal Article In: European Journal of Neuroscience, vol. 38, no. 12, pp. 3712–3720, 2013. @article{Shigihara2013, We used magnetoencephalography (MEG) to determine whether increasingly complex forms constituted from the same elements (lines) activate visual cortex with the same or different latencies. Twenty right-handed healthy adult volunteers viewed two different forms, lines and rhomboids, representing two levels of complexity. Our results showed that the earliest responses produced by lines and rhomboids in both striate and prestriate cortex had similar peak latencies (40 ms) although lines produced stronger responses than rhomboids. Dynamic causal modeling (DCM) showed that a parallel multiple input model to striate and prestriate cortex accounts best for the MEG response data. These results lead us to conclude that the perceptual hierarchy between lines and rhomboids is not mirrored by a temporal hierarchy in latency of activation and thus that a strategy of parallel processing appears to be used to construct forms, without implying that a hierarchical strategy may not be used in separate visual areas, in parallel. |
Julia M. Stephen; Brian A. Coffman; David B. Stone; Piyadasa Kodituwakku Differences in MEG gamma oscillatory power during performance of a prosaccade task in adolescents with FASD Journal Article In: Frontiers in Human Neuroscience, vol. 7, pp. 900, 2013. @article{Stephen2013, Fetal alcohol spectrum disorder (FASD) is characterized by a broad range of behavioral and cognitive deficits that impact the long-term quality of life for affected individuals. However, the underlying changes in brain structure and function associated with these cognitive impairments are not well-understood. Previous studies identified deficits in behavioral performance of prosaccade tasks in children with FASD. In this study, we investigated group differences in gamma oscillations during performance of a prosaccade task. We collected magnetoencephalography (MEG) data from 15 adolescents with FASD and 20 age-matched healthy controls (HC) with a mean age of 15.9 ± 0.4 years during performance of a prosaccade task. Eye movement was recorded and synchronized to the MEG data using an MEG compatible eye-tracker. The MEG data were analyzed relative to the onset of the visual saccade. Time-frequency analysis was performed using Fieldtrip with a focus on group differences in gamma-band oscillations. Following left target presentation, we identified four clusters over right frontal, right parietal, and left temporal/occipital cortex, with significantly different gamma-band (30-50 Hz) power between FASD and HC. Furthermore, visual M100 latencies described in Coffman etal. (2012) corresponded with increased gamma power over right central cortex in FASD only. Gamma-band differences were not identified for stimulus-averaged responses implying that these gamma-band differences were related to differences in saccade network functioning. These differences in gamma-band power may provide indications of atypical development of cortical networks in individuals with FASD. |
Durk Talsma; Brian J. White; Sebastiaan Mathôt; Douglas P. Munoz; Jan Theeuwes A retinotopic attentional trace after saccadic eye movements: Evidence from event-related potentials Journal Article In: Journal of Cognitive Neuroscience, vol. 25, no. 9, pp. 1563–1577, 2013. @article{Talsma2013, Saccadic eye movements are a major source of disruption to visual stability, yet we experience little of this disruption. We can keep track of the same object across multiple saccades. It is generally assumed that visual stability is due to the process of remapping, in which retinotopically organized maps are updated to compensate for the retinal shifts caused by eye movements. Recent behavioral and ERP evidence suggests that visual attention is also remapped, but that it may still leave a residual retinotopic trace immediately after a saccade. The current study was designed to further examine electrophysiological evidence for such a retinotopic trace by recording ERPs elicited by stimuli that were presented immediately after a saccade (80 msec SOA). Participants were required to maintain attention at a specific location (and to memorize this location) while making a saccadic eye movement. Immediately after the saccade, a visual stimulus was briefly presented at either the attended location (the same spatiotopic location), a location that matched the attended location retinotopically (the same retinotopic location), or one of two control locations. ERP data revealed an enhanced P1 amplitude for the stimulus presented at the retinotopically matched location, but a significant attenuation for probes presented at the original attended location. These results are consistent with the hypothesis that visuospatial attention lingers in retinotopic coordinates immediately following gaze shifts. |
Heng Ru May Tan; Hartmut Leuthold; Joachim Gross Gearing up for action: Attentive tracking dynamically tunes sensory and motor oscillations in the alpha and beta band Journal Article In: NeuroImage, vol. 82, pp. 634–644, 2013. @article{Tan2013, Allocation of attention during goal-directed behavior entails simultaneous processing of relevant and attenuation of irrelevant information. How the brain delegates such processes when confronted with dynamic (biological motion) stimuli and harnesses relevant sensory information for sculpting prospective responses remains unclear. We analyzed neuromagnetic signals that were recorded while participants attentively tracked an actor's pointing movement that ended at the location where subsequently the response-cue indicated the required response. We found the observers' spatial allocation of attention to be dynamically reflected in lateralized parieto-occipital alpha (8-12. Hz) activity and to have a lasting influence on motor preparation. Specifically, beta (16-25. Hz) power modulation reflected observers' tendency to selectively prepare for a spatially compatible response even before knowing the required one. We discuss the observed frequency-specific and temporally evolving neural activity within a framework of integrated visuomotor processing and point towards possible implications about the mechanisms involved in action observation. |
Marieke E. Nieuwenhuijzen; A. R. Backus; A. Bahramisharif; Christian F. Doeller; Ole Jensen; Marcel A. J. Gerven MEG-based decoding of the spatiotemporal dynamics of visual category perception Journal Article In: NeuroImage, vol. 83, pp. 1063–1073, 2013. @article{Nieuwenhuijzen2013, Visual processing is a complex task which is best investigated using sensitive multivariate analysis methods that can capture representation-specific brain activity over both time and space. In this study, we applied a multivariate decoding algorithm to MEG data of subjects engaged in passive viewing of images of faces, scenes, bodies and tools. We used reconstructed source-space time courses as input to the algorithm in order to localize brain regions involved in optimal image discrimination. Applying this method to the interval of 115 to 315. ms after stimulus onset, we show a focal localization of regression coefficients in the inferior occipital, middle occipital, and lingual gyrus that drive decoding of the different perceived image categories. Classifier accuracy was highest (over 90% correctly classified trials, compared to a chance level accuracy of 50%) when dissociating the perception of faces from perception of other object categories. Furthermore, we applied this method to each single time point to extract the temporal evolution of visual perception. This allowed for the detection of differences in visual category perception as early as 85. ms after stimulus onset. Furthermore, localizing the corresponding regression coefficients of each time point allowed us to capture the spatiotemporal dynamics of visual category perception. This revealed initial involvement of sources in the inferior occipital, inferior temporal and superior occipital gyrus. During sustained stimulation additional sources in the anterior inferior temporal gyrus and superior parietal gyrus became involved. We conclude that decoding of source-space MEG data provides a suitable method to investigate the spatiotemporal dynamics of ongoing cognitive processing. |
Emanuel N. Broeke; D. M. Hartgerink; J. Butler; Julien Lambert; André Mouraux Central sensitization increases the pupil dilation elicited by mechanical pinprick stimulation Journal Article In: Journal of Neurophysiology, vol. 53, no. 9, pp. 1689–1699, 2013. @article{Broeke2013, High frequency electrical stimulation (HFS) of skin nociceptors triggers central sensitization (CS), manifested as increased pinprick sensitivity of the skin surrounding the site of HFS. Our aim was to assess the effect of CS on pinprick‐evoked pupil dilation responses (PDRs) and pinprick‐evoked brain potentials (PEPs). We hypothesized that the increase in the positive wave of PEPs following HFS would result from an enhanced pinprick‐evoked phasic response of the locus coeruleus‐noradrenergic system (LC‐NS), indicated by enhanced PDRs. In fourteen healthy volunteers, 64 and 96 mN pinprick stimuli were delivered to the left and right forearms, before and twenty minutes after applying HFS to one of the two forearms. Both PEPs and pinprick‐evoked PDRs were recorded. After HFS, pinprick stimuli were perceived as more intense at the HFS treated arm compared to baseline and control site, and this increase was similar for both stimulation intensities. Importantly, the pinprick‐ evoked PDR was also increased and the increase was stronger for 64 as compared to 96 mN stimulation. This is in line with our previous results showing a stronger increase of the PEP positivity at 64 vs. 96 mN stimulation and suggests that the increase in PEP positivity observed in previous studies could relate, at least in part, to enhance LC‐NS activity. However, there was no increase of the PEP positivity in the present study, indicating that enhanced LC‐NS activity is not the only determinant of the HFS‐induced enhancement of PEPs. Altogether, our results indicate that PDRs are more sensitive for detecting CS than PEPs. |
Stan Van Pelt; Pascal Fries Visual stimulus eccentricity affects human gamma peak frequency Journal Article In: NeuroImage, vol. 78, pp. 439–447, 2013. @article{VanPelt2013, The peak frequency of neuronal gamma-band synchronization has received much attention in recent years. Gamma peak frequency shifts to higher frequency values for higher contrast, faster moving, and attended stimuli. In monkey V1, gamma peak frequency for a drifting grating is higher for a parafoveal as compared to an eccentric stimulus (Lima et al., 2010). This effect might be due to the cortical magnification factor: the higher cortical magnification for parafoveal stimuli increases the velocity with which the cortical representations of the moving grating stripes move across the cortical surface. Since faster moving stimuli lead to higher gamma frequency, a faster moving cortical representation might do the same. This explanation predicts that the eccentricity effect on gamma peak frequency is absent for stationary stimuli. To test this, we investigated the effect of eccentricity on gamma peak frequency by recording magnetoencephalography in human subjects while they viewed moving or stationary gratings. We found that both the moving and the stationary stimuli induced lower peak frequencies for larger eccentricities, arguing against an explanation based on the cortical magnification factor. We further investigated whether this eccentricity effect was explained by differences in the size or the spatial frequency of the expected cortical activation. Neither of those explained the eccentricity effect. We propose that the different stimulus and top-down factors leading to higher gamma peak frequency all result in higher stimulus salience, that salience is translated into gamma peak frequency, and that gamma peak frequency might subserve the preferential processing of neuronal activity induced by salient stimuli. |
Younes Zerouali; Jean Marc Lina; Boutheina Jemel Optimal eye-gaze fixation position for face-related neural responses Journal Article In: PLoS ONE, vol. 8, no. 6, pp. e60128, 2013. @article{Zerouali2013, It is generally agreed that some features of a face, namely the eyes, are more salient than others as indexed by behavioral diagnosticity, gaze-fixation patterns and evoked-neural responses. However, because previous studies used unnatural stimuli, there is no evidence so far that the early encoding of a whole face in the human brain is based on the eyes or other facial features. To address this issue, scalp electroencephalogram (EEG) and eye gaze-fixations were recorded simultaneously in a gaze-contingent paradigm while observers viewed faces. We found that the N170 indexing the earliest face-sensitive response in the human brain was the largest when the fixation position is located around the nasion. Interestingly, for inverted faces, this optimal fixation position was more variable, but mainly clustered in the upper part of the visual field (around the mouth). These observations extend the findings of recent behavioral studies, suggesting that the early encoding of a face, as indexed by the N170, is not driven by the eyes per se, but rather arises from a general perceptual setting (upper-visual field advantage) coupled with the alignment of a face stimulus to a stored face template. |
Junpeng Lao; Luca Vizioli; Roberto Caldara Culture modulates the temporal dynamics of global/local processing Journal Article In: Culture and Brain, vol. 1, no. 2-4, pp. 158–174, 2013. @article{Lao2013, Cultural differences in the way individuals from Western Caucasian (WC) and East Asian (EA) societies perceive and attend to visual information have been consistently reported in recent years. WC observers favor and perceive most efficiently the salient, local visual information by directing attention to focal objects. In contrast, EA observers show a bias towards global information, by preferentially attending elements in the background. However, the underlying neural mechanisms and the temporal dynamics of this striking cultural contrast have yet to be clarified. The combination of Navon figures, which contain both global and local features, and the measurement of neural adaptation constitute an ideal way to probe this issue. We recorded the electrophysiological signals of WC and EA observers while they actively matched culturally neutral geometric Navon shapes. In each trial, participants sequentially viewed and categorized an adapter shape followed by a target shape, as being either: identical; global congruent; local congruent; and different. We quantified the repetition suppression, a reduction in neural activity in stimulus sensitive regions following stimulus repetition, using a single-trial approach. A robust data-driven spatio-temporal analysis revealed at 80 ms a significant interaction between the culture of the observers and shape adaptation. EA observers showed sensitivity to global congruency on the attentional P1 component, whereas WC observers showed discrimination for global shapes at later stages. Our data revealed an early sensitivity to global and local shape cate- gorization, which is modulated by culture. This neural tuning could underlie more complex behavioral differences observed across human populations. |
Ada Le; Matthias Niemeier Left visual field preference for a bimanual grasping task with ecologically valid object sizes Journal Article In: Experimental Brain Research, vol. 230, pp. 187–196, 2013. @article{Le2013a, Grasping using two forelimbs in opposition to one another is evolutionary older than the hand with an opposable thumb (Whishaw and Coles in Behav Brain Res 77:135–148, 1996); yet, the mechanisms for bimanual grasps remain unclear. Similar to unimanual grasping, the localization of matching stable grasp points on an object is computationally expensive and so it makes sense for the signals to converge in a single cortical hemisphere. Indeed, bimanual grasps are faster and more accurate in the left visual field, and are disrupted if there is transcra- nial stimulation of the right hemisphere (Le and Niemeier in Exp Brain Res 224:263–273, 2013; Le et al. in Cereb Cortex. doi:10.1093/cercor/bht115, 2013). However, research so far has tested the right hemisphere dominance based on small objects only, which are usually grasped with one hand, whereas bimanual grasping is more com- monly used for objects that are too big for a single hand. Because grasping large objects might involve different neural circuits than grasping small objects (Grol et al. in J Neurosci 27:11877–11887, 2007), here we tested whether a left visual field/right hemisphere dominance for biman- ual grasping exists with large and thus more ecologically valid objects or whether the right hemisphere dominance is a function of object size. We asked participants to fixate to the left or right of an object and to grasp the object with the index and middle fingers of both hands. Consistent with previous observations, we found that for objects in the left visual field, the maximum grip apertures were scaled closer to the object width and were smaller and less variable, than for objects in the right visual field. Our results demonstrate that bimanual grasping is predominantly controlled by the right hemisphere, even in the context of grasping larger objects. |
Adrian K. C. Lee; Siddharth Rajaram; Jing Xia; Hari Bharadwaj; Eric D. Larson; Matti S. Hämäläinen; Barbara G. Shinn-Cunningham Auditory selective attention reveals preparatory activity in different cortical regions for selection based on source location and source pitch Journal Article In: Frontiers in Neuroscience, vol. 6, pp. 190, 2013. @article{Lee2013b, In order to extract information in a rich environment, we focus on different features that allow us to direct attention to whatever source is of interest. The cortical network deployed during spatial attention, especially in vision, is well characterized. For example, visuospatial attention engages a frontoparietal network including the frontal eye fields (FEFs), which modulate activity in visual sensory areas to enhance the representation of an attended visual object. However, relatively little is known about the neural circuitry controlling attention directed to non-spatial features, or to auditory objects or features (either spatial or non-spatial). Here, using combined magnetoencephalography (MEG) and anatomical information obtained from MRI, we contrasted cortical activity when observers attended to different auditory features given the same acoustic mixture of two simultaneous spoken digits. Leveraging the fine temporal resolution of MEG, we establish that activity in left FEF is enhanced both prior to and throughout the auditory stimulus when listeners direct auditory attention to target location compared to when they focus on target pitch. In contrast, activity in the left posterior superior temporal sulcus (STS), a region previously associated with auditory pitch categorization, is greater when listeners direct attention to target pitch rather than target location. This differential enhancement is only significant after observers are instructed which cue to attend, but before the acoustic stimuli begin. We therefore argue that left FEF participates more strongly in directing auditory spatial attention, while the left STS aids auditory object selection based on the non-spatial acoustic feature of pitch. |
Pavan Ramkumar; Mainak Jas; Sebastian Pannasch; Riitta Hari; Lauri Parkkonen Feature-specific information processing precedes concerted activation in human visual cortex Journal Article In: Journal of Neuroscience, vol. 33, no. 18, pp. 7691–7699, 2013. @article{Ramkumar2013, Current knowledge about the precise timing of visual input to the cortex relies largely on spike timings in monkeys and evoked-response latencies in humans. However, quantifying the activation onset does not unambiguously describe the timing of stimulus-feature-specific information processing. Here, we investigated the information content of the early human visual cortical activity by decoding low-level visual features from single-trial magnetoencephalographic (MEG) responses. MEG was measured from nine healthy subjects as they viewed annular sinusoidal gratings (spanning the visual field from 2 to 10° for a duration of 1 s), characterized by spatial frequency (0.33 cycles/degree or 1.33 cycles/degree) and orientation (45° or 135°); gratings were either static or rotated clockwise or anticlockwise from 0 to 180°. Time-resolved classifiers using a 20 ms moving window exceeded chance level at 51 ms (the later edge of the window) for spatial frequency, 65 ms for orientation, and 98 ms for rotation direction. Decoding accuracies of spatial frequency and orientation peaked at 70 and 90 ms, respectively, coinciding with the peaks of the onset evoked responses. Within-subject time-insensitive pattern classifiers decoded spatial frequency and orientation simultaneously (mean accuracy 64%, chance 25%) and rotation direction (mean 82%, chance 50%). Classifiers trained on data from other subjects decoded the spatial frequency (73%), but not the orientation, nor the rotation direction. Our results indicate that unaveraged brain responses contain decodable information about low-level visual features already at the time of the earliest cortical evoked responses, and that representations of spatial frequency are highly robust across individuals. |
Linsey Roijendijk; Jason Farquhar; Marcel A. J. Gerven; Ole Jensen; Stan Gielen In: PLoS ONE, vol. 8, no. 12, pp. e80489, 2013. @article{Roijendijk2013, OBJECTIVE: Covert visual spatial attention is a relatively new task used in brain computer interfaces (BCIs) and little is known about the characteristics which may affect performance in BCI tasks. We investigated whether eccentricity and task difficulty affect alpha lateralization and BCI performance. APPROACH: We conducted a magnetoencephalography study with 14 participants who performed a covert orientation discrimination task at an easy or difficult stimulus contrast at either a near (3.5°) or far (7°) eccentricity. Task difficulty was manipulated block wise and subjects were aware of the difficulty level of each block. MAIN RESULTS: Grand average analyses revealed a significantly larger hemispheric lateralization of posterior alpha power in the difficult condition than in the easy condition, while surprisingly no difference was found for eccentricity. The difference between task difficulty levels was significant in the interval between 1.85 s and 2.25 s after cue onset and originated from a stronger decrease in the contralateral hemisphere. No significant effect of eccentricity was found. Additionally, single-trial classification analysis revealed a higher classification rate in the difficult (65.9%) than in the easy task condition (61.1%). No effect of eccentricity was found in classification rate. SIGNIFICANCE: Our results indicate that manipulating the difficulty of a task gives rise to variations in alpha lateralization and that using a more difficult task improves covert visual spatial attention BCI performance. The variations in the alpha lateralization could be caused by different factors such as an increased mental effort or a higher visual attentional demand. Further research is necessary to discriminate between them. We did not discover any effect of eccentricity in contrast to results of previous research. |
Chie Nakatani; Mojtaba Chehelcheraghi; Behnaz Jarrahi; Hironori Nakatani; Cees Leeuwen Cross-frequency phase synchrony around the saccade period as a correlate of perceiver's internal state Journal Article In: Frontiers in Systems Neuroscience, vol. 7, pp. 18, 2013. @article{Nakatani2013a, In active vision, eye-movements depend on perceivers' internal state. We investigated peri-fixation brain activity for internal state-specific tagging. Human participants performed a task, in which a visual object was presented for identification in lateral visual field, to which they moved their eyes as soon as possible from a central fixation point. Next, a phrase appeared in the same location; the phrase could either be an easy or hard question about the object, answered by pressing one of two alternative response buttons, or it could be an instruction to simply press one of these two buttons. Depending on whether these messages were blocked or randomly mixed, one of two different internal states was induced: either the task was known in advance or it wasn't. Eye movements and electroencephalogram (EEG) were recorded simultaneously during task performance. Using eye-event-time-locked averaging and independent component analysis, saccade- and fixation-related components were identified. Coss-frequency phase-synchrony was observed between the alpha/beta1 ranges of fixation-related and beta2/gamma1 ranges of saccade-related activity 50 ms prior to fixation onset in the mixed-phrase condition only. We interpreted this result as evidence for internal state-specific tagging. |
Hironori Nakatani; Cees Leeuwen Antecedent occipital alpha band activity predicts the impact of oculomotor events in perceptual switching Journal Article In: Frontiers in Systems Neuroscience, vol. 7, pp. 19, 2013. @article{Nakatani2013, Oculomotor events such as blinks and saccades transiently interrupt the visual input and, even though this mostly goes undetected, these brief interruptions could still influence the percept. In particular, both blinking and saccades facilitate switching in ambiguous figures such as the Necker cube. To investigate the neural state antecedent to these oculomotor events during the perception of an ambiguous figure, we measured the human scalp electroencephalogram (EEG). When blinking led to perceptual switching, antecedent occipital alpha band activity exhibited a transient increase in amplitude. When a saccade led to switching, a series of transient increases and decreases in amplitude was observed in the antecedent occipital alpha band activity. Our results suggest that the state of occipital alpha band activity predicts the impact of oculomotor events on the percept. |
Andrey R. Nikolaev; Peter Jurica; Chie Nakatani; Gijs Plomp; Cees Leeuwen Visual encoding and fixation target selection in free viewing: Presaccadic brain potentials Journal Article In: Frontiers in Systems Neuroscience, vol. 7, pp. 26, 2013. @article{Nikolaev2013, In scrutinizing a scene, the eyes alternate between fixations and saccades. During a fixation, two component processes can be distinguished: visual encoding and selection of the next fixation target. We aimed to distinguish the neural correlates of these processes in the electrical brain activity prior to a saccade onset. Participants viewed color photographs of natural scenes, in preparation for a change detection task. Then, for each participant and each scene we computed an image heat map, with temperature representing the duration and density of fixations. The temperature difference between the start and end points of saccades was taken as a measure of the expected task-relevance of the information concentrated in specific regions of a scene. Visual encoding was evaluated according to whether subsequent change was correctly detected. Saccades with larger temperature difference were more likely to be followed by correct detection than ones with smaller temperature differences. The amplitude of presaccadic activity over anterior brain areas was larger for correct detection than for detection failure. This difference was observed for short "scrutinizing" but not for long "explorative" saccades, suggesting that presaccadic activity reflects top-down saccade guidance. Thus, successful encoding requires local scanning of scene regions which are expected to be task-relevant. Next, we evaluated fixation target selection. Saccades "moving up" in temperature were preceded by presaccadic activity of higher amplitude than those "moving down". This finding suggests that presaccadic activity reflects attention deployed to the following fixation location. Our findings illustrate how presaccadic activity can elucidate concurrent brain processes related to the immediate goal of planning the next saccade and the larger-scale goal of constructing a robust representation of the visual scene. |
Daniel Belyusar; Adam C. Snyder; Hans Peter Frey; Mark R. Harwood; Josh Wallman; John J. Foxe Oscillatory alpha-band suppression mechanisms during the rapid attentional shifts required to perform an anti-saccade task Journal Article In: NeuroImage, vol. 65, pp. 395–407, 2013. @article{Belyusar2013, Neuroimaging has demonstrated anatomical overlap between covert and overt attention systems, although behavioral and electrophysiological studies have suggested that the two systems do not rely on entirely identical circuits or mechanisms. In a parallel line of research, topographically-specific modulations of alpha-band power (~. 8-14. Hz) have been consistently correlated with anticipatory states during tasks requiring covert attention shifts. These tasks, however, typically employ cue-target-interval paradigms where attentional processes are examined across relatively protracted periods of time and not at the rapid timescales implicated during overt attention tasks. The anti-saccade task, where one must first covertly attend for a peripheral target, before executing a rapid overt attention shift (i.e. a saccade) to the opposite side of space, is particularly well-suited for examining the rapid dynamics of overt attentional deployments. Here, we asked whether alpha-band oscillatory mechanisms would also be associated with these very rapid overt shifts, potentially representing a common neural mechanism across overt and covert attention systems. High-density electroencephalography in conjunction with infra-red eye-tracking was recorded while participants engaged in both pro- and anti-saccade task blocks. Alpha power, time-locked to saccade onset, showed three distinct phases of significantly lateralized topographic shifts, all occurring within a period of less than 1. s, closely reflecting the temporal dynamics of anti-saccade performance. Only two such phases were observed during the pro-saccade task. These data point to substantially more rapid temporal dynamics of alpha-band suppressive mechanisms than previously established, and implicate oscillatory alpha-band activity as a common mechanism across both overt and covert attentional deployments. |
S. E. Bosch; Sebastiaan F. W. Neggers; Stefan Van der Stigchel The role of the frontal eye fields in oculomotor competition: Image-guided TMS enhances contralateral target selection Journal Article In: Cerebral Cortex, vol. 23, no. 4, pp. 824–832, 2013. @article{Bosch2013, In order to execute a correct eye movement to a target in a search display, a saccade program toward the target element must be activated, while saccade programs toward distracting elements must be inhibited. The aim of the present study was to elucidate the role of the frontal eye fields (FEFs) in oculomotor competition. Functional magnetic resonance imaging-guided single-pulse transcranial magnetic stimulation (TMS) was administered over either the left FEF, the right FEF, or the vertex (control site) at 3 time intervals after target presentation, while subjects performed an oculomotor capture task. When TMS was applied over the FEF contralateral to the visual field where a target was presented, there was less interference of an ipsilateral distractor compared with FEF stimulation ipsilateral to the target's visual field or TMS over vertex. Furthermore, TMS over the FEFs decreased latencies of saccades to the contralateral visual field, irrespective of whether the saccade was directed to the target or to the distractor. These findings show that single-pulse TMS over the FEFs enhances the selection of a target in the contralateral visual field and decreases saccade latencies to the contralateral visual field. |
Harriet R. Brown; Karl J. Friston The functional anatomy of attention: A DCM study Journal Article In: Frontiers in Human Neuroscience, vol. 7, pp. 784, 2013. @article{Brown2013, Recent formulations of attention—in terms of predictive coding—associate attentional gain with the expected precision of sensory information. Formal models of the Posner paradigm suggest that validity effects can be explained in a principled (Bayes optimal) fashion in terms of a cue-dependent setting of precision or gain on the sensory channels reporting anticipated target locations, which is updated selectively by invalid targets. This normative model is equipped with a biologically plausible process theory in the form of predictive coding, where precision is encoded by the gain of superficial pyramidal cells reporting prediction error. We used dynamic causal modeling to assess the evidence in magnetoencephalographic responses for cue-dependent and top-down updating of superficial pyramidal cell gain. Bayesian model comparison suggested that it is almost certain that differences in superficial pyramidal cells gain—and its top-down modulation—contribute to observed responses; and we could be more than 80% certain that anticipatory effects on post-synaptic gain are limited to visual (extrastriate) sources. These empirical results speak to the role of attention in optimizing perceptual inference and its formulation in terms of predictive coding. |
2012 |
Peter R. Murphy; Ian H. Robertson; Darren Allen; Robert Hester; Redmond G. O'Connell An electrophysiological signal that precisely tracks the emergence of error awareness Journal Article In: Frontiers in Human Neuroscience, vol. 6, pp. 65, 2012. @article{Murphy2012, Recent electrophysiological research has sought to elucidate the neural mechanisms necessary for the conscious awareness of action errors. Much of this work has focussed on the error positivity (Pe), a neural signal that is specifically elicited by errors that have been consciously perceived. While awareness appears to be an essential prerequisite for eliciting the Pe, the precise functional role of this component has not been identified. Twenty-nine participants performed a novel variant of the Go/No-go Error Awareness Task (EAT) in which awareness of commission errors was indicated via a separate speeded manual response. Independent component analysis (ICA) was used to isolate the Pe from other stimulus- and response-evoked signals. Single-trial analysis revealed that Pe peak latency was highly correlated with the latency at which awareness was indicated. Furthermore, the Pe was more closely related to the timing of awareness than it was to the initial erroneous response. This finding was confirmed in a separate study which derived IC weights from a control condition in which no indication of awareness was required, thus ruling out motor confounds. A receiver-operating-characteristic (ROC) curve analysis showed that the Pe could reliably predict whether an error would be consciously perceived up to 400ms before the average awareness response. Finally, Pe latency and amplitude were found to be significantly correlated with overall error awareness levels between subjects. Our data show for the first time that the temporal dynamics of the Pe trace the emergence of error awareness. These findings have important implications for interpreting the results of clinical EEG studies of error processing. |
José P. Ossandón; Selim Onat; Dario Cazzoli; Thomas Nyffeler; René M. Müri; Peter König Unmasking the contribution of low-level features to the guidance of attention Journal Article In: Neuropsychologia, vol. 50, no. 14, pp. 3478–3487, 2012. @article{Ossandon2012, The role of low-level stimulus-driven control in the guidance of overt visual attention has been difficult to establish because low- and high-level visual content are spatially correlated within natural visual stimuli. Here we show that impairment of parietal cortical areas, either permanently by a lesion or reversibly by repetitive transcranial magnetic stimulation (rTMS), leads to fixation of locations with higher values of low-level features as compared to control subjects or in a no-rTMS condition. Moreover, this unmasking of stimulus-driven control crucially depends on the intrahemispheric balance between top-down and bottom-up cortical areas. This result suggests that although in normal behavior high-level features might exert a strong influence, low-level features do contribute to guide visual selection during the exploration of complex natural stimuli. |
Ryan J. Vaden; Nathan L. Hutcheson; Lesley A. McCollum; Jonathan Kentros; Kristina M. Visscher Older adults, unlike younger adults, do not modulate alpha power to suppress irrelevant information Journal Article In: NeuroImage, vol. 63, no. 3, pp. 1127–1133, 2012. @article{Vaden2012, This study examines the neural mechanisms through which younger and older adults ignore irrelevant information, a process that is necessary to effectively encode new memories. Some age-related memory deficits have been linked to a diminished ability to dynamically gate sensory input, resulting in problems inhibiting the processing of distracting stimuli. Whereas oscillatory power in the alpha band (8-12. Hz) over visual cortical areas is thought to dynamically gate sensory input in younger adults, it is not known whether older adults use the same mechanism to gate out sensory input. Here we identified a task in which both older and younger adults could suppress the processing of irrelevant sensory stimuli, allowing us to use electroencephalography (EEG) to explore the neural activity associated with suppression of visual processing. As expected, we found that the younger adults' suppression of visual processing was correlated with robust modulation of alpha oscillatory power. However, older adults did not modulate alpha power to suppress processing of visual information. These results demonstrate that suppression of alpha power is not necessary to inhibit the processing of distracting stimuli in older adults, suggesting the existence of alternative strategies for suppressing irrelevant, potentially distracting information. |
Juan E. Kamienkowski; Matias J. Ison; Rodrigo Quian Quiroga; Mariano Sigman Fixation-related potentials in visual search: A combined EEG and eye tracking study Journal Article In: Journal of Vision, vol. 12, no. 7, pp. 1–20, 2012. @article{Kamienkowski2012, We report a study of concurrent eye movements and electroencephalographic (EEG) recordings while subjects freely explored a search array looking for hidden targets. We describe a sequence of fixation-event related potentials (fERPs) that unfolds during ; 400 ms following each fixation. This sequence highly resembles the event-related responses in a replay experiment, in which subjects kept fixation while a sequence of images occurred around the fovea simulating the spatial and temporal patterns during the free viewing experiment. Similar responses were also observed in a second control experiment where the appearance of stimuli was controlled by the experimenters and presented at the center of the screen. We also observed a relatively early component (;150 ms) that distinguished between targets and distractors only in the freeviewing condition. We present a novel approach to match the critical properties of two conditions (targets/distractors), which can be readily adapted to other paradigms to investigate EEG components during free eye-movements. |
Marc R. Kamke; Michelle G. Hall; Harley F. Lye; Martin V. Sale; Laura R. Fenlon; Timothy J. Carroll; Stephan Riek; Jason B. Mattingley Visual attentional load influences plasticity in the human motor cortex Journal Article In: Journal of Neuroscience, vol. 32, no. 20, pp. 7001–7008, 2012. @article{Kamke2012, Neural plasticity plays a critical role in learning, memory, and recovery from injury to the nervous system. Although much is known about the physical and physiological determinants of plasticity, little is known about the influence of cognitive factors. In this study, we investigated whether selective attention plays a role in modifying changes in neural excitability reflecting long-term potentiation (LTP)-like plasticity. We induced LTP-like effects in the hand area of the human motor cortex using transcranial magnetic stimulation (TMS). During the induction of plasticity, participants engaged in a visual detection task with either low or high attentional demands. Changes in neural excitability were assessed by measuring motor-evoked potentials in a small hand muscle before and after the TMS procedures. In separate experiments plasticity was induced either by paired associative stimulation (PAS) or intermittent theta-burst stimulation (iTBS). Because these procedures induce different forms of LTP-like effects, they allowed us to investigate the generality of any attentional influence on plasticity. In both experiments reliable changes in motor cortex excitability were evident under low-load conditions, but this effect was eliminated under high-attentional load. In a third experiment we investigated whether the attentional task was associated with ongoing changes in the excitability of motor cortex, but found no difference in evoked potentials across the levels of attentional load. Our findings indicate that in addition to their role in modifying sensory processing, mechanisms of attention can also be a potent modulator of cortical plasticity. |
Marc R. Kamke; Harrison E. Vieth; David Cottrell; Jason B. Mattingley Parietal disruption alters audiovisual binding in the sound-induced flash illusion Journal Article In: NeuroImage, vol. 62, no. 3, pp. 1334–1341, 2012. @article{Kamke2012a, Selective attention and multisensory integration are fundamental to perception, but little is known about whether, or under what circumstances, these processes interact to shape conscious awareness. Here, we used transcranial magnetic stimulation (TMS) to investigate the causal role of attention-related brain networks in multisensory integration between visual and auditory stimuli in the sound-induced flash illusion. The flash illusion is a widely studied multisensory phenomenon in which a single flash of light is falsely perceived as multiple flashes in the presence of irrelevant sounds. We investigated the hypothesis that extrastriate regions involved in selective attention, specifically within the right parietal cortex, exert an influence on the multisensory integrative processes that cause the flash illusion. We found that disruption of the right angular gyrus, but not of the adjacent supramarginal gyrus or of a sensory control site, enhanced participants' veridical perception of the multisensory events, thereby reducing their susceptibility to the illusion. Our findings suggest that the same parietal networks that normally act to enhance perception of attended events also play a role in the binding of auditory and visual stimuli in the sound-induced flash illusion. |
Kohitij Kar; Bart Krekelberg Transcranial electrical stimulation over visual cortex evokes phosphenes with a retinal origin Journal Article In: Journal of Neurophysiology, vol. 108, no. 8, pp. 2173–2178, 2012. @article{Kar2012, Transcranial electrical stimulation (tES) is a promising therapeutic tool for a range of neurological diseases. Understanding how the small currents used in tES spread across the scalp and penetrate the brain will be important for the rational design of tES therapies. Alternating currents applied transcranially above visual cortex induce the perception of flashes of light (phosphenes). This makes the visual system a useful model to study tES. One hypothesis is that tES generates phosphenes by direct stimulation of the cortex underneath the transcranial electrode. Here, we provide evidence for the alternative hypothesis that phosphenes are generated in the retina by current spread from the occipital electrode. Building on the existing literature, we first confirm that phosphenes are induced at lower currents when electrodes are placed farther away from visual cortex and closer to the eye. Second, we explain the temporal frequency tuning of phosphenes based on the well-known response properties of primate retinal ganglion cells. Third, we show that there is no difference in the time it takes to evoke phosphenes in the retina or by stimulation above visual cortex. Together, these findings suggest that phosphenes induced by tES over visual cortex originate in the retina. From this, we infer that tES currents spread well beyond the area of stimulation and are unlikely to lead to focal neural activation. Novel stimulation protocols that optimize current distributions are needed to overcome these limitations of tES. |
Sangita Dandekar; Jian Ding; Claudio M. Privitera; Thom Carney; Stanley A. Klein The fixation and saccade P3 Journal Article In: PLoS ONE, vol. 7, no. 11, pp. e48761, 2012. @article{Dandekar2012, Although most instances of object recognition during natural viewing occur in the presence of saccades, the neural correlates of objection recognition have almost exclusively been examined during fixation. Recent studies have indicated that there are post-saccadic modulations of neural activity immediately following eye movement landing; however, whether post-saccadic modulations affect relatively late occurring cognitive components such as the P3 has not been explored. The P3 as conventionally measured at fixation is commonly used in brain computer interfaces, hence characterizing the post-saccadic P3 could aid in the development of improved brain computer interfaces that allow for eye movements. In this study, the P3 observed after saccadic landing was compared to the P3 measured at fixation. No significant differences in P3 start time, temporal persistence, or amplitude were found between fixation and saccade trials. Importantly, sensory neural responses canceled in the target minus distracter comparisons used to identify the P3. Our results indicate that relatively late occurring cognitive neural components such as the P3 are likely less sensitive to post saccadic modulations than sensory neural components and other neural activity occurring shortly after eye movement landing. Furthermore, due to the similarity of the fixation and saccade P3, we conclude that the P3 following saccadic landing could possibly be used as a viable signal in brain computer interfaces allowing for eye movements. |
Marco Davare; A. Zénon; Gilles Pourtois; Michel Desmurget; Etienne Olivier Role of the medial part of the intraparietal sulcus in implementing movement direction Journal Article In: Cerebral Cortex, vol. 22, no. 6, pp. 1382–1394, 2012. @article{Davare2012, The contribution of the posterior parietal cortex (PPC) to visually guided movements has been originally inferred from observations made in patients suffering from optic ataxia. Subsequent electrophysiological studies in monkeys and functional imaging data in humans have corroborated the key role played by the PPC in sensorimotor transformations underlying goal-directed movements, although the exact contribution of this structure remains debated. Here, we used transcranial magnetic stimulation (TMS) to interfere transiently with the function of the left or right medial part of the intraparietal sulcus (mIPS) in healthy volunteers performing visually guided movements with the right hand. We found that a "virtual lesion" of either mIPS increased the scattering in initial movement direction (DIR), leading to longer trajectory and prolonged movement time, but only when TMS was delivered 100-160 ms before movement onset and for movements directed toward contralateral targets. Control experiments showed that deficits in DIR consequent to mIPS virtual lesions resulted from an inappropriate implementation of the motor command underlying the forthcoming movement and not from an inaccurate computation of the target localization. The present study indicates that mIPS plays a causal role in implementing specifically the direction vector of visually guided movements toward objects situated in the contralateral hemifield. |
Steven L. Franconeri; Jason M. Scimeca; Jessica C. Roth; Sarah A. Helseth; Lauren E. Kahn Flexible visual processing of spatial relationships Journal Article In: Cognition, vol. 122, no. 2, pp. 210–227, 2012. @article{Franconeri2012, Visual processing breaks the world into parts and objects, allowing us not only to examine the pieces individually, but also to perceive the relationships among them. There is work exploring how we perceive spatial relationships within structures with existing representations, such as faces, common objects, or prototypical scenes. But strikingly, there is little work on the perceptual mechanisms that allow us to flexibly represent arbitrary spatial relationships, e.g., between objects in a novel room, or the elements within a map, graph or diagram. We describe two classes of mechanism that might allow such judgments. In the simultaneous class, both objects are selected concurrently. In contrast, we propose a sequential class, where objects are selected individually over time. We argue that this latter mechanism is more plausible even though it violates our intuitions. We demonstrate that shifts of selection do occur during spatial relationship judgments that feel simultaneous, by tracking selection with an electrophysiological correlate. We speculate that static structure across space may be encoded as a dynamic sequence across time. Flexible visual spatial relationship processing may serve as a case study of more general visual relation processing beyond space, to other dimensions such as size or numerosity. |
Wei-Kuang Liang; Chi-Hung Juan Modulation of motor control in saccadic behaviors by TMS over the posterior parietal cortex Journal Article In: Journal of Neurophysiology, vol. 108, no. 3, pp. 741–752, 2012. @article{Liang2012, The right posterior parietal cortex (rPPC) has been found to be critical in shaping visual selection and distractor-induced saccade curvature in the context of predictive as well as nonpredictive visual cues by means of transcranial magnetic stimulation (TMS) interference. However, the dynamic details of how distractor-induced saccade curvatures are affected by rPPC TMS have not yet been investigated. This study aimed to elucidate the key dynamic properties that cause saccades to curve away from distractors with different degrees of curvature in various TMS and target predictability conditions. Stochastic optimal feedback control theory was used to model the dynamics of the TMS saccade data. This allowed estimation of torques, which was used to identify the critical dynamic mechanisms producing saccade curvature. The critical mechanisms of distractor-induced saccade curvatures were found to be the motor commands and torques in the transverse direction. When an unpredictable saccade target occurred with rPPC TMS, there was an initial period of greater distractor-induced torque toward the side opposite the distractor in the transverse direction, immediately followed by a relatively long period of recovery torque that brought the deviated trace back toward the target. The results imply that the mechanisms of distractor-induced saccade curvature may be comprised of two mechanisms: the first causing the initial deviation and the second bringing the deviated trace back toward the target. The pattern of the initial torque in the transverse direction revealed the former mechanism. Conversely, the later mechanism could be well explained as a consequence of the control policy in this model. To summarize, rPPC TMS increased the initial torque away from the distractor as well as the recovery torque toward the target. |
Annmarie MacNamara; Joseph Schmidt; Gregory J. Zelinsky; Greg Hajcak Electrocortical and ocular indices of attention to fearful and neutral faces presented under high and low working memory load Journal Article In: Biological Psychology, vol. 91, no. 3, pp. 349–356, 2012. @article{MacNamara2012, Working memory load reduces the late positive potential (LPP), consistent with the notion that functional activation of the DLPFC attenuates neural indices of sustained attention. Visual attention also modulates the LPP. In the present study, we sought to determine whether working memory load might exert its influence on ERPs by reducing fixations to arousing picture regions. We simultaneously recorded eye-tracking and EEG while participants performed a working memory task interspersed with the presentation of task-irrelevant fearful and neutral faces. As expected, fearful compared to neutral faces elicited larger N170 and LPP amplitudes; in addition, working memory load reduced the N170 and the LPP. Participants made more fixations to arousing regions of neutral faces and faces presented under high working memory load. Therefore, working memory load did not induce avoidance of arousing picture regions and visual attention cannot explain load effects on the N170 and LPP. |
Michael Plöchl; José P. Ossandón; Peter König Combining EEG and eye tracking: Identification, characterization, and correction of eye movement artifacts in electroencephalographic data Journal Article In: Frontiers in Human Neuroscience, vol. 6, pp. 278, 2012. @article{Ploechl2012, Eye movements introduce large artifacts to electroencephalographic recordings (EEG) and thus render data analysis difficult or even impossible. Trials contaminated by eye movement and blink artifacts have to be discarded, hence in standard EEG-paradigms subjects are required to fixate on the screen. To overcome this restriction, several correction methods including regression and blind source separation have been proposed. Yet, there is no automated standard procedure established. By simultaneously recording eye movements and 64-channel-EEG during a guided eye movement paradigm, we investigate and review the properties of eye movement artifacts, including corneo-retinal dipole changes, saccadic spike potentials and eyelid artifacts, and study their interrelations during different types of eye- and eyelid movements. In concordance with earlier studies our results confirm that these artifacts arise from different independent sources and that depending on electrode site, gaze direction, and choice of reference these sources contribute differently to the measured signal. We assess the respective implications for artifact correction methods and therefore compare the performance of two prominent approaches, namely linear regression and independent component analysis (ICA). We show and discuss that due to the independence of eye artifact sources, regression-based correction methods inevitably over- or under-correct individual artifact components, while ICA is in principle suited to address such mixtures of different types of artifacts. Finally, we propose an algorithm, which uses eye tracker information to objectively identify eye-artifact related ICA-components (ICs) in an automated manner. In the data presented here, the algorithm performed very similar to human experts when those were given both, the topographies of the ICs and their respective activations in a large amount of trials. Moreover it performed more reliable and almost twice as effective than human experts when those had to base their decision on IC topographies only. Furthermore, a receiver operating characteristic (ROC) analysis demonstrated an optimal balance of false positive and false negative at an area under curve (AUC) of more than 0.99. Removing the automatically detected ICs from the data resulted in removal or substantial suppression of ocular artifacts including microsaccadic spike potentials, while the relevant neural signal remained unaffected. In conclusion the present work aims at a better understanding of individual eye movement artifacts, their interrelations and the respective implications for eye artifact correction. Additionally, the proposed ICA-procedure provides a tool for optimized detection and correction of eye movement-related artifact components. |
Federico Raimondo; Juan E. Kamienkowski; Mariano Sigman; Diego Fernandez Slezak CUDAICA: GPU optimization of infomax-ICA EEG analysis Journal Article In: Computational Intelligence and Neuroscience, vol. 2012, pp. 1–8, 2012. @article{Raimondo2012, In recent years, Independent Component Analysis (ICA) has become a standard to identify relevant dimensions of the data in neuroscience. ICA is a very reliable method to analyze data but it is, computationally, very costly. The use of ICA for online analysis of the data, used in brain computing interfaces, results are almost completely prohibitive. We show an increase with almost no cost (a rapid video card) of speed of ICA by about 25 fold. The EEG data, which is a repetition of many independent signals in multiple channels, is very suitable for processing using the vector processors included in the graphical units. We profiled the implementation of this algorithm and detected two main types of operations responsible of the processing bottleneck and taking almost 80% of computing time: vector-matrix and matrix-matrix multiplications. By replacing function calls to basic linear algebra functions to the standard CUBLAS routines provided by GPU manufacturers, it does not increase performance due to CUDA kernel launch overhead. Instead, we developed a GPU-based solution that, comparing with the original BLAS and CUBLAS versions, obtains a 25x increase of performance for the ICA calculation. |
Robert M. G. Reinhart; Richard P. Heitz; Braden A. Purcell; Pauline K. Weigand; Jeffrey D. Schall; Geoffrey F. Woodman Homologous mechanisms of visuospatial working memory maintenance in macaque and human: Properties and sources Journal Article In: Journal of Neuroscience, vol. 32, no. 22, pp. 7711–7722, 2012. @article{Reinhart2012, Although areas of frontal cortex are thought to be critical for maintaining information in visuospatial working memory, the event-related potential (ERP) index of maintenance is found over posterior cortex in humans. In the present study, we reconcile these seemingly contradictory findings. Here, we show that macaque monkeys and humans exhibit the same posterior ERP signature of working memory maintenance that predicts the precision of the memory-based behavioral responses. In addition, we show that the specific pattern of rhythmic oscillations in the alpha band, recently demonstrated to underlie the human visual working memory ERP component, is also present in monkeys. Next, we concurrently recorded intracranial local field potentials from two prefrontal and another frontal cortical area to determine their contribution to the surface potential indexing maintenance. The local fields in the two prefrontal areas, but not the cortex immediately posterior, exhibited amplitude modulations, timing, and relationships to behavior indicating that they contribute to the generation of the surface ERP component measured from the distal posterior electrodes. Rhythmic neural activity in the theta and gamma bands during maintenance provided converging support for the engagement of the same brain regions. These findings demonstrate that nonhuman primates have homologous electrophysiological signatures of visuospatial working memory to those of humans and that a distributed neural network, including frontal areas, underlies the posterior ERP index of visuospatial working memory maintenance. |
Yangqing Xu; Steven L. Franconeri The head of the table: Marking the "front" of an object is tightly linked with selection Journal Article In: Journal of Neuroscience, vol. 32, no. 4, pp. 1408–1412, 2012. @article{Xu2012, Objects in the world do not have a surface that can be objectively labeled the "front." We impose this designation on one surface of an object according to several cues, including which surface is associated with the most task-relevant information or the direction of motion of an object. However, when these cues are competing, weak, or absent, we can also flexibly assign one surface as the front. One possibility is that this assignment is guided by the location of the "spotlight" of selection, where the selected region becomes the front. Here we used an electrophysiological correlate to show a direct temporal link between object structure assignments and the spatial locus of selection. We found that when human participants viewed a shape whose front and back surfaces were ambiguous, seeing a given surface as front was associated with selectively attending to that location. In Experiment 1, this pattern occurred during directed rapid (every 1 s) switches in structural percepts. In Experiment 2, this pattern occurred during spontaneous reversals, from 900 ms before to 600 ms after the reported percept. These results suggest that the distribution of selective attention might guide the organization of object structure. |
2011 |
Shlomit Yuval-Greenberg; Leon Y. Deouell Scalp-recorded induced gamma-band responses to auditory stimulation and its correlations with saccadic muscle-activity Journal Article In: Brain Topography, vol. 24, no. 1, pp. 30–39, 2011. @article{YuvalGreenberg2011, We previously showed that the transient broadband induced gamma-band response in EEG (iGBRtb) appearing around 200-300 ms following a visual stimulus reflects the contraction of extra-ocular muscles involved in the execution of saccades, rather than neural oscillations. Several previous studies reported induced gamma-band responses also following auditory stimulation. It is still an open question whether, similarly to visual paradigms, such auditory paradigms are also sensitive to the saccadic confound. In the current study we address this question using simultaneous eye-tracking and EEG recordings during an auditory oddball paradigm. Subjects were instructed to respond to a rare target defined by sound source location, while fixating on a central screen. Results show that, similar to what was found in visual paradigms, saccadic rate displayed typical temporal dynamics including a post-stimulus decrease followed by an increase. This increase was more moderate, had a longer latency, and was less consistent across subjects than was found in the visual case. Crucially, the temporal dynamics of the induced gamma response were similar to those of saccadic-rate modulation. This suggests that the auditory induced gamma-band responses recorded on the scalp may also be affected by saccadic muscle activity. |
Qing Yang; Zoï Kapoula Distinct control of initiation and metrics of memory-guided saccades and vergence by the FEF: A TMS study Journal Article In: PLoS ONE, vol. 6, no. 5, pp. e20322, 2011. @article{Yang2011, BACKGROUND: The initiation of memory guided saccades is known to be controlled by the frontal eye field (FEF). Recent physiological studies showed the existence of an area close to FEF that controls also vergence initiation and execution. This study is to explore the effect of transcranial magnetic simulation (TMS) over FEF on the control of memory-guided saccade-vergence eye movements. METHODOLOGY/PRINCIPAL FINDINGS: Subjects had to make an eye movement in dark towards a target flashed 1 sec earlier (memory delay); the location of the target relative to fixation point was such as to require either a vergence along the median plane, or a saccade, or a saccade with vergence; trials were interleaved. Single pulse TMS was applied on the left or right FEF; it was delivered at 100 ms after the end of memory delay, i.e. extinction of fixation LED that was the "go" signal. Twelve healthy subjects participated in the study. TMS of left or right FEF prolonged the latency of all types of eye movements; the increase varied from 21 to 56 ms and was particularly strong for the divergence movements. This indicates that FEF is involved in the initiation of all types of memory guided movement in the 3D space. TMS of the FEF also altered the accuracy but only for leftward saccades combined with either convergence or divergence; intrasaccadic vergence also increased after TMS of the FEF. CONCLUSIONS/SIGNIFICANCE: The results suggest anisotropy in the quality of space memory and are discussed in the context of other known perceptual motor anisotropies. |
Minnan Xu-Wilson; Jing Tian; Reza Shadmehr; David S. Zee TMS perturbs saccade trajectories and unmasks an internal feedback controller for saccades Journal Article In: Journal of Neuroscience, vol. 31, no. 32, pp. 11537–11546, 2011. @article{XuWilson2011, When we applied a single pulse of transcranial magnetic stimulation (TMS) to any part of the human head during a saccadic eye movement, the ongoing eye velocity was reduced as early as 45 ms after the TMS, and lasted ∼32 ms. The perturbation to the saccade trajectory was not due to a mechanical effect of the lid on the eye (e.g., from blinks). When the saccade involved coordinated movements of both the eyes and the lids, e.g., in vertical saccades, TMS produced a synchronized inhibition of the motor commands to both eye and lid muscles. The TMS-induced perturbation of the eye trajectory did not show habituation with repetition, and was present in both pro-saccades and anti-saccades. Despite the perturbation, the eye trajectory was corrected within the same saccade with compensatory motor commands that guided the eyes to the target. This within-saccade correction did not rely on visual input, suggesting that the brain monitored the oculomotor commands as the saccade unfolded, maintained a real-time estimate of the position of the eyes, and corrected for the perturbation. TMS disrupted saccades regardless of the location of the coil on the head, suggesting that the coil discharge engages a nonhabituating startle-like reflex system. This system affects ongoing motor commands upstream of the oculomotor neurons, possibly at the level of the superior colliculus or omnipause neurons. Therefore, a TMS pulse centrally perturbs saccadic motor commands, which are monitored possibly via efference copy and are corrected via internal feedback. |
Jacob Jolij; H. Steven Scholte; Simon Gaal; Timothy L. Hodgson; Victor A. F. Lamme Act quickly, decide later: Long-latency visual processing underlies perceptual decisions but not reflexive behavior Journal Article In: Journal of Cognitive Neuroscience, vol. 23, no. 12, pp. 3734–3745, 2011. @article{Jolij2011, Humans largely guide their behavior by their visual representation of the world. Recent studies have shown that visual information can trigger behavior within 150 msec, suggesting that visually guided responses to external events, in fact, precede conscious awareness of those events. However, is such a view correct? By using a texture discrimination task, we show that the brain relies on long-latency visual processing in order to guide perceptual decisions. Decreasing stimulus saliency leads to selective changes in long-latency visually evoked potential components reflecting scene segmentation. These latency changes are accompanied by almost equal changes in simple RTs and points of subjective simultaneity. Furthermore, we find a strong correlation between individual RTs and the latencies of scene segmentation related components in the visually evoked potentials, showing that the processes underlying these late brain potentials are critical in triggering a response. However, using the same texture stimuli in an antisaccade task, we found that reflexive, but erroneous, prosaccades, but not antisaccades, can be triggered by earlier visual processes. In other words: The brain can act quickly, but decides late. Differences between our study and earlier findings suggesting that action precedes conscious awareness can be explained by assuming that task demands determine whether a fast and unconscious, or a slower and conscious, representation is used to initiate a visually guided response. |
Zoï Kapoula; Qing Yang; Norman Sabbah; Marine Vernet Different effects of double-pulse TMS of the posterior parietal cortex on reflexive and voluntary saccades Journal Article In: Frontiers in Human Neuroscience, vol. 5, pp. 114, 2011. @article{Kapoula2011, Gap and overlap tasks are widely used to promote automatic versus controlled saccades. This study examines the hypothesis that the right posterior parietal cortex (PPC) is differently involved in the two tasks. Twelve healthy students participated in the experiment. We used double-pulse transcranial magnetic stimulation (dTMS) on the right PPC, the first pulse delivered at the target onset and the second 65 or 80 ms later. Each subject performed several blocks of gap or overlap task with or without dTMS. Eye movements were recorded with an Eyelink device. The results show an increase of latency of saccades after dTMS of the right PPC for both tasks but for different time windows (0-80 ms for the gap task, 0-65 ms for the overlap task). Moreover, for rightward saccades the coefficient of variation of latency increased in the gap task but decreased in the overlap task. Finally, in the gap task and for leftward saccades only, dTMS at 0-80 ms decreased the amplitude and the speed of saccades. Although the study is preliminary and needs further investigation in detail, the results support the hypothesis that the right PPC is involved differently in the initiation of the saccades for the two tasks: in the gap task the PPC controls saccade triggering while in the overlap task it could be a relay to the Frontal Eye Fields which is known to control voluntary saccades, e.g., memory-guided and perhaps the controlled saccades in the overlap task The results have theoretical and clinical significance as gap-overlap tasks are easy to perform even in advanced age and in patients with neurodegenerative diseases. |
Yosuke Kita; Atsuko Gunji; Yuki Inoue; Takaaki Goto; Kotoe Sakihara; Makiko Kaga; Masumi Inagaki; Toru Hosokawa Self-face recognition in children with autism spectrum disorders: A near-infrared spectroscopy study Journal Article In: Brain and Development, vol. 33, no. 6, pp. 494–503, 2011. @article{Kita2011, It is assumed that children with autism spectrum disorders (ASD) have specificities for self-face recognition, which is known to be a basic cognitive ability for social development. In the present study, we investigated neurological substrates and potentially influential factors for self-face recognition of ASD patients using near-infrared spectroscopy (NIRS). The subjects were 11 healthy adult men, 13 normally developing boys, and 10 boys with ASD. Their hemodynamic activities in the frontal area and their scanning strategies (eye-movement) were examined during self-face recognition. Other factors such as ASD severities and self-consciousness were also evaluated by parents and patients, respectively. Oxygenated hemoglobin levels were higher in the regions corresponding to the right inferior frontal gyrus than in those corresponding to the left inferior frontal gyrus. In two groups of children these activities reflected ASD severities, such that the more serious ASD characteristics corresponded with lower activity levels. Moreover, higher levels of public self-consciousness intensified the activities, which were not influenced by the scanning strategies. These findings suggest that dysfunction in the right inferior frontal gyrus areas responsible for self-face recognition is one of the crucial neural substrates underlying ASD characteristics, which could potentially be used to evaluate psychological aspects such as public self-consciousness. |
Christian Kluge; Markus Bauer; Alexander P. Leff; Hans-Jochen Heinze; Raymond J. Dolan; Jon Driver; Alexander Paul Plasticity of human auditory-evoked fields induced by shock conditioning and contingency reversal Journal Article In: Proceedings of the National Academy of Sciences, vol. 108, no. 30, pp. 12545–12550, 2011. @article{Kluge2011, We used magnetoencephalography (MEG) to assess plasticity of human auditory cortex induced by classical conditioning and contingency reversal. Participants listened to random sequences of high or low tones. A first baseline phase presented these without further associations. In phase 2, one of the frequencies (CS(+)) was paired with shock on half its occurrences, whereas the other frequency (CS(-)) was not. In phase 3, the contingency assigning CS(+) and CS(-) was reversed. Conditioned pupil dilation was observed in phase 2 but extinguished in phase 3. MEG revealed that, during phase-2 initial conditioning, the P1m, N1m, and P2m auditory components, measured from sensors over auditory temporal cortex, came to distinguish between CS(+) and CS(-). After contingency reversal in phase 3, the later P2m component rapidly reversed its selectivity (unlike the pupil response) but the earlier P1m did not, whereas N1m showed some new learning but not reversal. These results confirm plasticity of human auditory responses due to classical conditioning, but go further in revealing distinct constraints on different levels of the auditory hierarchy. The later P2m component can reverse affiliation immediately in accord with an updated expectancy after contingency reversal, whereas the earlier auditory components cannot. These findings indicate distinct cognitive and emotional influences on auditory processing. |
Neil G. Muggleton; Roger Kalla; Chi-Hung Juan; Vincent Walsh Dissociating the contributions of human frontal eye fields and posterior parietal cortex to visual search Journal Article In: Journal of Neurophysiology, vol. 105, no. 6, pp. 2891–2896, 2011. @article{Muggleton2011, Imaging, lesion, and transcranial magnetic stimulation (TMS) studies have implicated a number of regions of the brain in searching for a target defined by a combination of attributes. The necessity of both frontal eye fields (FEF) and posterior parietal cortex (PPC) in task performance has been shown by the application of TMS over these regions. The effects of stimulation over these two areas have, thus far, proved to be remarkably similar and the only dissociation reported being in the timing of their involvement. We tested the hypotheses that 1) FEF contributes to performance in terms of visual target detection (possibly by modulation of activity in extrastriate areas with respect to the target), and 2) PPC is involved in translation of visual information for action. We used a task where the presence (and location) of the target was indicated by an eye movement. Task disruption was seen with FEF TMS (with reduced accuracy on the task) but not with PPC stimulation. When a search task requiring a manual response was presented, disruption with PPC TMS was seen. These results show dissociation of FEF and PPC contributions to visual search performance and that PPC involvement seems to be dependent on the response required by the task, whereas this is not the case for FEF. This supports the idea of FEF involvement in visual processes in a manner that might not depend on the required response, whereas PPC seems to be involved when a manual motor response to a stimulus is required. |
Hironori Nakatani; Nicoletta Orlandi; Cees Van Leeuwen Precisely timed oculomotor and parietal EEG activity in perceptual switching Journal Article In: Cognitive Neurodynamics, vol. 5, no. 4, pp. 399–409, 2011. @article{Nakatani2011, Blinks and saccades cause transient interruptions of visual input. To investigate how such effects influence our perceptual state, we analyzed the time courses of blink and saccade rates in relation to perceptual switching in the Necker cube. Both time courses of blink and saccade rates showed peaks at different moments along the switching process. A peak in blinking rate appeared 1,000 ms prior to the switching responses. Blinks occurring around this peak were associated with subsequent switching to the preferred interpretation of the Necker cube. Saccade rates showed a peak 150 ms prior to the switching response. The direction of saccades around this peak was predictive of the perceived orientation of the Necker cube afterwards. Peak blinks were followed and peak saccades were preceded by transient parietal theta band activity indicating the changing of the perceptual interpretation. Precisely-timed blinks, therefore, can initiate perceptual switching, and precisely-timed saccades can facilitate an ongoing change of interpretation. © 2011 The Author(s). |
Nicole Naue; Daniel Strüber; Ingo Fründ; Jeanette Schadow; Daniel Lenz; Stefan Rach; Ursula Körner; Christoph S. Herrmann Gamma in motion: Pattern reversal elicits stronger gamma-band responses than motion Journal Article In: NeuroImage, vol. 55, no. 2, pp. 808–817, 2011. @article{Naue2011, Previous studies showed higher gamma-band responses (GBRs, ≈ 40. Hz) of the electroencephalogram (EEG) for moving compared to stationary stimuli. However, it is unclear whether this modulation by motion reflects a special responsiveness of the GBR to the stimulus feature ''motion,'' or whether GBR enhancements of similar magnitude can be elicited also by a salient change within a static stimulus that does not include motion.Therefore, we measured the EEG of healthy subjects watching stationary square wave gratings of high contrast that either started to move or reversed their black and white pattern shortly after their onset. The strong contrast change of the pattern reversal represented a salient but motionless change within the grating that was compared to the onset of the stationary grating and the motion onset. Induced and evoked GBRs were analyzed for all three display conditions. In order to assess the influenceof fixational eye movements on the induced GBRs, we also examined the time courses of microsaccade rates during the three display conditions. Amplitudes of both evoked and induced GBRs were stronger for pattern reversal than for motion onset. There was no significant amplitude difference between the onsets of the stationary and moving gratings. However, mean frequencies of the induced GBR were ~10. Hz higher in response to the onsets of moving compared to stationary gratings. Furthermore, the modulations of the induced GBR did not parallel the modulations of microsaccade rate, indicating that our induced GBRs reflect neuronal processes. These results suggest that, within the gamma-band range, the encoding of moving gratings in early visual cortex is primarily based on an upward frequency shift, whereas contrast changes within static gratings are reflected by amplitude enhancement. |
Andrey R. Nikolaev; Chie Nakatani; Gijs Plomp; Peter Jurica; Cees Leeuwen Eye fixation-related potentials in free viewing identify encoding failures in change detection Journal Article In: NeuroImage, vol. 56, no. 3, pp. 1598–1607, 2011. @article{Nikolaev2011, We considered the hypothesis that spontaneous dissociation between the direction of attention and eye movement causes encoding failure in change detection. We tested this hypothesis by analyzing eye fixation-related potentials (EFRP) at the encoding stage of a change blindness task; when participants freely inspect a scene containing an unmarked target region, in which a change will occur in a subsequent presentation. We measured EFRP amplitude prior to the execution of a saccade, depending on its starting or landing position relative to the target region. For those landings inside the target region, we found a difference in EFRP between correct detection and failure. Overall, correspondence between EFRP amplitude and the size of the saccade predicted successful detection of change; lack of correspondence was followed by change blindness. By contrast, saccade sizes and fixation durations around the target region were unrelated to subsequent change detection. Since correspondence between EFRP and eye movement indicates that overt attention was given to the target region, we concluded that overt attention is needed for successful encoding and that dissociation between eye movement and attention leads to change blindness. |
Snigdha Banerjee; Adam C. Snyder; Sophie Molholm; John J. Foxe In: Journal of Neuroscience, vol. 31, no. 27, pp. 9923–9932, 2011. @article{Banerjee2011, Oscillatory alpha-band activity (8-15 Hz) over parieto-occipital cortex in humans plays an important role in suppression of processing for inputs at to-be-ignored regions of space, with increased alpha-band power observed over cortex contralateral to locations expected to contain distractors. It is unclear whether similar processes operate during deployment of spatial attention in other sensory modalities. Evidence from lesion patients suggests that parietal regions house supramodal representations of space. The parietal lobes are prominent generators of alpha oscillations, raising the possibility that alpha is a neural signature of supramodal spatial attention. Furthermore, when spatial attention is deployed within vision, processing of task-irrelevant auditory inputs at attended locations is also enhanced, pointing to automatic links between spatial deployments across senses. Here, we asked whether lateralized alpha-band activity is also evident in a purely auditory spatial-cueing task and whether it had the same underlying generator configuration as in a purely visuospatial task. If common to both sensory systems, this would provide strong support for "supramodal" attention theory. Alternately, alpha-band differences between auditory and visual tasks would support a sensory-specific account. Lateralized shifts in alpha-band activity were indeed observed during a purely auditory spatial task. Crucially, there were clear differences in scalp topographies of this alpha activity depending on the sensory system within which spatial attention was deployed. Findings suggest that parietally generated alpha-band mechanisms are central to attentional deployments across modalities but that they are invoked in a sensory-specific manner. The data support an "interactivity account," whereby a supramodal system interacts with sensory-specific control systems during deployment of spatial attention. |
Genevieve Z. Steiner; Robert J. Barry Pupillary responses and event-related potentials as indices of the orienting reflex Journal Article In: Psychophysiology, vol. 48, no. 12, pp. 1648–1655, 2011. @article{Steiner2011, This study examined skin conductance responses, the late positive complex of the event-related potential, and pupillary dilation responses as autonomic and central correlates of the orienting reflex (OR) in the context of indifferent and significant stimuli. In particular, we aimed to clarify the inconsistencies surrounding the pupillary dilation response as an OR index. An auditory dishabituation paradigm was employed, and physiological measures were recorded from 24 participants. Response decrement to a repeated stimulus, response recovery to a change stimulus, and subsequent dishabituation were assessed. Findings confirmed expectations that the skin conductance response and the late positive complex are indices of the OR. The pupillary dilation response, however, demonstrated an unexpected sensitivity to stimulus novelty only, while the prestimulus measure of tonic pupil diameter showed the significance effect that was expected of the phasic measure. Together, these findings argue against the suggestion that the pupillary dilation response is an OR index. The diverse results obtained from this experiment contribute to our understanding of the OR, and provide impetus for further research with a variety of paradigm manipulations. |
Marine Vernet; Qing Yang; Zoï Kapoula Guiding binocular saccades during reading: A TMS study of the PPC Journal Article In: Frontiers in Human Neuroscience, vol. 5, pp. 14, 2011. @article{Vernet2011, Reading is an activity based on complex sequences of binocular saccades and fixations. During saccades, the eyes do not move together perfectly: saccades could end with a misalignment, compromising fused vision. During fixations, small disconjugate drift can partly reduce this misalignment. We hypothesized that maintaining eye alignment during reading involves active monitoring from posterior parietal cortex (PPC); this goes against traditional views considering only downstream binocular control. Nine young adults read a text; transcranial magnetic stimulation (TMS) was applied over the PPC every 5 ± 0.2 s. Eye movements were recorded binocularly with Eyelink II. Stimulation had three major effects: (1) disturbance of eye alignment during fixation; (2) increase of saccade disconjugacy leading to eye misalignment; (3) decrease of eye alignment reduction during fixation drift. The effects depend on the side; the right PPC was more involved in maintaining alignment over the motor sequence. Thus, the PPC is actively involved in the control of binocular eye alignment during reading, allowing clear vision. Cortical activation during reading is related to linguistic processes and motor control per se. The study might be of interest for the understanding of deficits of binocular coordination, encountered in several populations, e.g., in children with dyslexia. |
Ali Mazaheri; Nicholas E. DiQuattro; Jesse Bengson; Joy J. Geng Pre-stimulus activity predicts the winner of top-down vs. bottom-up attentional selection Journal Article In: PLoS ONE, vol. 6, no. 2, pp. e16243, 2011. @article{Mazaheri2011, Our ability to process visual information is fundamentally limited. This leads to competition between sensory information that is relevant for top-down goals and sensory information that is perceptually salient, but task-irrelevant. The aim of the present study was to identify, from EEG recordings, pre-stimulus and pre-saccadic neural activity that could predict whether top-down or bottom-up processes would win the competition for attention on a trial-by-trial basis. We employed a visual search paradigm in which a lateralized low contrast target appeared alone, or with a low (i.e., non-salient) or high contrast (i.e., salient) distractor. Trials with a salient distractor were of primary interest due to the strong competition between top-down knowledge and bottom-up attentional capture. Our results demonstrated that 1) in the 1-sec pre-stimulus interval, frontal alpha (8-12 Hz) activity was higher on trials where the salient distractor captured attention and the first saccade (bottom-up win); and 2) there was a transient pre-saccadic increase in posterior-parietal alpha (7-8 Hz) activity on trials where the first saccade went to the target (top-down win). We propose that the high frontal alpha reflects a disengagement of attentional control whereas the transient posterior alpha time-locked to the saccade indicates sensory inhibition of the salient distractor and suppression of bottom-up oculomotor capture. |
Chang-Mao Chao; Philip Tseng; Tzu-Yu Hsu; Jia-Han Su; Ovid J. L. Tzeng; Daisy L. Hung; Neil G. Muggleton; Chi-Hung Juan Predictability of saccadic behaviors is modified by transcranial magnetic stimulation over human posterior parietal cortex Journal Article In: Human Brain Mapping, vol. 32, no. 11, pp. 1961–1972, 2011. @article{Chao2011, Predictability in the visual environment provides a powerful cue for efficient processing of scenes and objects. Recently, studies have suggested that the directionality and magnitude of saccade curvature can be informative as to how the visual system processes predictive information. The pres-ent study investigated the role of the right posterior parietal cortex (rPPC) in shaping saccade curva-tures in the context of predictive and non-predictive visual cues. We used an orienting paradigm that incorporated manipulation of target location predictability and delivered transcranial magnetic stimulation (TMS) over rPPC. Participants were presented with either an informative or uninforma-tive cue to upcoming target locations. Our results showed that rPPC TMS generally increased sac-cade latency and saccade error rates. Intriguingly, rPPC TMS increased curvatures away from the distractor only when the target location was unpredictable and decreased saccadic errors towards the distractor. These effects on curvature and accuracy were not present when the target location was predictable. These results dissociate the strong contingency between saccade latency and saccade curvature and also indicate that rPPC plays an important role in allocating and suppressing attention to distractors when the target demands visual disambiguation. Furthermore, the present study sug-gests that, like the frontal eye fields, rPPC is critically involved in determining saccade curvature and the generation of saccadic behaviors under conditions of differing target predictability. |
Sangita Dandekar; Claudio M. Privitera; Thom Carney; Stanley A. Klein Neural saccadic response estimation during natural viewing Sangita Journal Article In: Journal of Neurophysiology, vol. 107, no. 4, pp. 1776–1790, 2011. @article{Dandekar2011, Studying neural activity during natural viewing conditions is not often attempted. Isolating the neural response of a single saccade is necessary to study neural activity during natural viewing; however, the close temporal spacing of saccades that occurs during natural viewing makes it difficult to determine the response to a single saccade. Herein, a general linear model (GLM) approach is applied to estimate the EEG neural saccadic response for different segments of the saccadic main sequence separately. It is determined that, in visual search conditions, neural responses estimated by conventional event-related averaging are significantly and systematically distorted relative to GLM estimates due to the close temporal spacing of saccades during visual search. Before the GLM is applied, analyses are applied that demonstrate that saccades during visual search with intersaccadic spacings as low as 100-150 ms do not exhibit significant refractory effects. Therefore, saccades displaying different intersaccadic spacings during visual search can be modeled using the same regressor in a GLM. With the use of the GLM approach, neural responses were separately estimated for five different ranges of saccade amplitudes during visual search. Occipital responses time locked to the onsets of saccades during visual search were found to account for, on average, 79 percent of the variance of EEG activity in a window 90-200 ms after the onsets of saccades for all five saccade amplitude ranges that spanned a range of 0.2-6.0 degrees. A GLM approach was also used to examine the lateralized ocular artifacts associated with saccades. Possible extensions of the methods presented here to account for the superposition of microsaccades in event-related EEG studies conducted in nominal fixation conditions are discussed. |
Sven-Thomas Graupner; Sebastian Pannasch; Boris M. Velichkovsky In: International Journal of Psychophysiology, vol. 80, no. 1, pp. 54–62, 2011. @article{Graupner2011, Attention, visual information processing, and oculomotor control are integrated functions of closely related brain mechanisms. Recently, it was shown that the processing of visual distractors appearing during a fixation is modulated by the amplitude of its preceding saccade (Pannasch & Velichkovsky, 2009). So far, this was demonstrated only at the behavioral level in terms of saccadic inhibition. The present study investigated distractor-related brain activity with cortical eye fixation-related potentials (EFRPs). Moreover, the following saccade was included as an additional classification criterion. Eye movements and EFRPs were recorded during free visual exploration of paintings. During some of the fixations, a visual distractor was shown as an annulus around the fixation position, 100. ms after the fixation onset. The saccadic context of a fixation was classified by its preceding and following saccade amplitudes with the cut-off criterion set to 4° of visual angle. The prolongation of fixation duration induced by distractors was largest for fixations preceded and followed by short saccades. EFRP data revealed a difference in distractor-related P2 amplitude between the saccadic context conditions, following the same trend as in eye movements. Furthermore, influences of the following saccade amplitude on the latency of the saccadic inhibition and on the N1 amplitude were found. The EFRP results cannot be explained by the influence of saccades per se since this bias was removed by subtracting the baseline from the distractor EFRP. Rather, the data suggest that saccadic context indicates differences in how information is processed within single visual fixations. |