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2013 |
Lisa Kloft; Benedikt Reuter; Anja Riesel; Norbert Kathmann Impaired volitional saccade control: First evidence for a new candidate endophenotype in obsessive-compulsive disorder Journal Article In: European Archives of Psychiatry and Clinical Neuroscience, vol. 263, pp. 215–222, 2013. @article{Kloft2013, Recent research suggests that patients with obsessive-compulsive disorder (OCD) have deficits in the volitional control of saccades. Specific evidence comes from increased latencies of saccadic eye movements when they were volitionally executed but not when they were visually guided. The present study sought to test whether this deviance represents a cognitive endophenotype. To this end, first-degree relatives of OCD patients as genetic risk carriers were compared with OCD patients and healthy controls without a family history of OCD. Furthermore, as volitional response generation comprises selection and initiation of the required response, the study also sought to specify the cognitive mechanisms underlying impaired volitional response generation. Twenty-two unaffected first-degree relatives of OCD patients, 22 unmedicated OCD patients, and 22 healthy comparison subjects performed two types of volitional saccade tasks measuring response selection or only response initiation, respectively. Visually guided saccades were used as a control condition. Our results showed that unaffected first-degree relatives and OCD patients were significantly slowed compared to healthy comparison subjects in volitional response selection. Patients and relatives did not differ from each other. There was no group difference in the visually guided control condition. Taken together, the study provides first evidence that dysfunctional volitional response selection is a candidate endophenotype for OCD. |
Megan Freeth; Tom Foulsham; Alan Kingstone What affects social attention? Social presence, eye contact and autistic traits Journal Article In: PLoS ONE, vol. 8, no. 1, pp. e53286, 2013. @article{Freeth2013, Social understanding is facilitated by effectively attending to other people and the subtle social cues they generate. In order to more fully appreciate the nature of social attention and what drives people to attend to social aspects of the world, one must investigate the factors that influence social attention. This is especially important when attempting to create models of disordered social attention, e.g. a model of social attention in autism. Here we analysed participants' viewing behaviour during one-to-one social interactions with an experimenter. Interactions were conducted either live or via video (social presence manipulation). The participant was asked and then required to answer questions. Experimenter eye-contact was either direct or averted. Additionally, the influence of participant self-reported autistic traits was also investigated. We found that regardless of whether the interaction was conducted live or via a video, participants frequently looked at the experimenter's face, and they did this more often when being asked a question than when answering. Critical differences in social attention between the live and video interactions were also observed. Modifications of experimenter eye contact influenced participants' eye movements in the live interaction only; and increased autistic traits were associated with less looking at the experimenter for video interactions only. We conclude that analysing patterns of eye-movements in response to strictly controlled video stimuli and natural real-world stimuli furthers the field's understanding of the factors that influence social attention. |
Teresa C. Frohman; Scott L. Davis; Shin Beh; Benjamin M. Greenberg; Gina Remington; Elliot M. Frohman Uhthoff's phenomena in MS - clinical features and pathophysiology Journal Article In: Nature Reviews Neurology, vol. 9, no. 9, pp. 535–540, 2013. @article{Frohman2013, In the late 19(th) century, Wilhelm Uhthoff reported on a series of patients with acute optic neuritis who manifested similar recurrent, stereotyped visual symptoms that were of paroxysmal onset, short in duration, and reversible. These 'Uhthoff's phenomena', which are a feature of multiple sclerosis (MS) and other demyelinating diseases, can be triggered by factors including the perimenstrual period, exercise, infection, fever, exposure to high ambient temperatures, and psychological stress. Here, we characterize the clinical, pathophysiological and neurotherapeutic challenges associated with Uhthoff's phenomena, and discuss the differentiation of these events from other paroxysmal, acute or subacute changes in functional capabilities and neurological symptoms in MS. For instance, whereas MS exacerbations are contingent on immune dysregulation, Uhthoff's phenomena are predicated on ion channel modifications, in conjunction with thermoregulatory derangements that transiently alter the conduction properties of demyelinated axons. An understanding of these pathophysiological underpinnings of Uhthoff's phenomena is germane to their recognition and timely treatment. |
Franziska Geringswald; Anne Herbik; Michael B. Hoffmann; Stefan Pollmann Contextual cueing impairment in patients with age-related macular degeneration Journal Article In: Journal of Vision, vol. 13, no. 3, pp. 1–18, 2013. @article{Geringswald2013, Visual attention can be guided by past experience of regularities in our visual environment. In the contextual cueing paradigm, incidental learning of repeated distractor configurations speeds up search times compared to random search arrays. Concomitantly, fewer fixations and more direct scan paths indicate more efficient visual exploration in repeated search arrays. In previous work, we found that simulating a central scotoma in healthy observers eliminated this search facilitation. Here, we investigated contextual cueing in patients with age-related macular degeneration (AMD) who suffer from impaired foveal vision. AMD patients performed visual search using only their more severely impaired eye (n = 13) as well as under binocular viewing (n = 16). Normal-sighted controls developed a significant contextual cueing effect. In comparison, patients showed only a small nonsignificant advantage for repeated displays when searching with their worse eye. When searching binocularly, they profited from contextual cues, but still less than controls. Number of fixations and scan pattern ratios showed a comparable pattern as search times. Moreover, contextual cueing was significantly correlated with acuity in monocular search. Thus, foveal vision loss may lead to impaired guidance of attention by contextual memory cues. |
Fiona C. Glen; Nicholas D. Smith; David P. Crabb Saccadic eye movements and face recognition performance in patients with central glaucomatous visual field defects Journal Article In: Vision Research, vol. 82, pp. 42–51, 2013. @article{Glen2013, Patients with more advanced glaucoma are likely to experience problems with everyday visual tasks such as face recognition. However, some patients still perform well at face recognition despite their visual field (VF) defects. This study investigated whether certain eye movement patterns are associated with better performance in the Cambridge Face Memory Test. For patients with bilateral VF defects in their central 10° of VF, making larger saccades appeared to be associated with better face recognition performance (rho = 0.60 |
Esther G. González; Linda Lillakas; Alexander Lam; Brenda L. Gallie; Martin J. Steinbach Horizontal saccade dynamics after childhood monocular enucleation Journal Article In: Investigative Ophthalmology & Visual Science, vol. 54, no. 10, pp. 6463–6471, 2013. @article{Gonzalez2013, PURPOSE: We investigated the effects of monocularity on oculomotor control by examining the characteristics of the horizontal saccades of people with one eye, and comparing them to those of a group of age-matched controls who viewed the stimuli monocularly and binocularly. METHODS: Participants were tested in a no-gap, no-overlap saccadic task using a video-based remote eye tracker. One group consisted of unilaterally eye enucleated participants (N = 15; mean age, 31.27 years), the other of age-matched people with normal binocular vision (N = 18; mean age, 30.17 years). RESULTS: The horizontal saccade dynamics of enucleated people are similar to those of people with normal binocularity when they view monocularly and, with the exception of latency, when they view binocularly. The data show that the monocular saccades of control and enucleated observers have longer latencies than the binocular saccades of the control group, the saccades of the enucleated observers are as accurate as those of the controls viewing monocularly or binocularly, smaller saccades are more accurate than the larger ones, and abducting saccades are faster than adducting saccades. CONCLUSIONS: Our data suggest that the true monocularity produced by early enucleation does not result in slower visual processing in the afferent (sensory) pathway, or in deficits in the efferent (motor) pathways of the saccadic system. Possible mechanisms to account for the effects of monocular vision on saccades are discussed. |
Martin Gorges; Hans Peter Müller; Dorothée Lulé; Albert C. Ludolph; Elmar H. Pinkhardt; Jan Kassubek In: Brain Connectivity, vol. 3, no. 3, pp. 265–272, 2013. @article{Gorges2013a, In addition to the skeleto-motor deficits, patients with Parkinson's disease (PD) frequently present with oculomotor dysfunctions such as impaired smooth pursuit and saccadic abnormalities. There is increasing evidence for an impaired cortical function to be responsible for oculomotor deficits that are associated with lack of inhibitory control; however, these pathomechanisms still remain poorly understood. By means of "task-free" resting-state functional magnetic resonance imaging (rs-fMRI), functional connectivity changes in PD within the default mode network (DMN) have been reported. The aim of this study was to investigate whether altered functional connectivity within the DMN was correlated with oculomotor parameter changes in PD. Twelve PD patients and 13 matched healthy controls underwent rs-fMRI at 1.5 T and videooculography (VOG) using Eye-Link-System. Rs-fMRI seed-based region-to-region connectivity analysis was performed, including medial prefrontal cortex (mPFC), medial temporal lobe (MTL), posterior cingulate cortex (PCC), and hippocampal formation (HF); while VOG examination comprised ocular reactive saccades, smooth pursuit, and executive tests. Rs-fMRI analysis demonstrated a decreased region-to-region functional connectivity between mPFC and PCC as well as increased connectivity between bilateral HF in PD compared with controls. In VOG, patients and controls differed in terms of executive tests outcome, smooth pursuit eye movement, and visually guided reactive saccades but not in peak eye velocity. A significant relationship was observed between saccadic accuracy and functional connectivity strengths between MTL and PCC. These results suggest that PD-associated changes of DMN connectivity are correlated with PD-associated saccadic hypometria, in particular in the vertical direction. |
Joshua A. Granek; Laure Pisella; John Stemberger; Alain Vighetto; Yves Rossetti; Lauren E. Sergio Decoupled visually-guided reaching in optic ataxia: Differences in motor control between canonical and non-canonical orientations in space Journal Article In: PLoS ONE, vol. 8, no. 12, pp. e86138, 2013. @article{Granek2013, Guiding a limb often involves situations in which the spatial location of the target for gaze and limb movement are not congruent (i.e. have been decoupled). Such decoupled situations involve both the implementation of a cognitive rule (i.e. strategic control) and the online monitoring of the limb position relative to gaze and target (i.e. sensorimotor recalibration). To further understand the neural mechanisms underlying these different types of visuomotor control, we tested patient IG who has bilateral caudal superior parietal lobule (SPL) damage resulting in optic ataxia (OA), and compared her performance with six age-matched controls on a series of center-out reaching tasks. The tasks comprised 1) directing a cursor that had been rotated (180° or 90°) within the same spatial plane as the visual display, or 2) moving the hand along a different spatial plane than the visual display (horizontal or para-sagittal). Importantly, all conditions were performed towards visual targets located along either the horizontal axis (left and right; which can be guided from strategic control) or the diagonal axes (top-left and top-right; which require on-line trajectory elaboration and updating by sensorimotor recalibration). The bilateral OA patient performed much better in decoupled visuomotor control towards the horizontal targets, a canonical situation in which well-categorized allocentric cues could be utilized (i.e. guiding cursor direction perpendicular to computer monitor border). Relative to neurologically intact adults, IG's performance suffered towards diagonal targets, a non-canonical situation in which only less-categorized allocentric cues were available (i.e. guiding cursor direction at an off-axis angle to computer monitor border), and she was therefore required to rely on sensorimotor recalibration of her decoupled limb. We propose that an intact caudal SPL is crucial for any decoupled visuomotor control, particularly when relying on the realignment between vision and proprioception without reliable allocentric cues towards non-canonical orientations in space. |
Michael A. Grubb; Nancy J. Minshew; David J. Heeger; Marisa Carrasco Exogenous spatial attention: Evidence for intact functioning in adults with autism spectrum disorder Journal Article In: Journal of Vision, vol. 13, no. 14, pp. 1–13, 2013. @article{Grubb2013, Deficits or atypicalities in attention have been reported in individuals with autism spectrum disorder (ASD), yet no consensus on the nature of these deficits has emerged. We conducted three experiments that paired a peripheral precue with a covert discrimination task, using protocols for which the effects of covert exogenous spatial attention on early vision have been well established in typically developing populations. Experiment 1 assessed changes in contrast sensitivity, using orientation discrimination of a contrast-defined grating; Experiment 2 evaluated the reduction of crowding in the visual periphery, using discrimination of a letter-like figure with flanking stimuli at variable distances; and Experiment 3 assessed improvements in visual search, using discrimination of the same letter-like figure with a variable number of distractor elements. In all three experiments, we found that exogenous attention modulated visual discriminability in a group of high-functioning adults with ASD and that it did so in the same way and to the same extent as in a matched control group. We found no evidence to support the hypothesis that deficits in exogenous spatial attention underlie the emergence of core ASD symptomatology. |
Christoph Helmchen; Stefan Glasauer; Andreas Sprenger Inverse eye position dependency of downbeat nystagmus in midline medullary lesion Journal Article In: Journal of Neurology, vol. 260, no. 11, pp. 2908–2910, 2013. @article{Helmchen2013, Downbeat nystagmus (DBN) is a persisting ocular motor sign most often found in vestibulo-cerebellar midline lesions. DBN typically increases on lateral and downward gaze and decreases with upward gaze [3], and thereby obeys Alexander's law which states that the slow phase velocity (SPV) is higher with gaze in the fast phase direction of nystagmus compared with gaze in the slow phase direction [11]. DBN may reverse into upward beating nystagmus on upward gaze or in the supine position [3, 4]. Only exceptionally, DBN may occur in midline pontomedullary [12], pontine [6] or medullary [1, 8] brainstem lesions. Current pathophysiological models on DBN are based on a dysfunction of the cerebellar flocculus and an impaired cerebellar negative feedback loop to the brainstem neural integrator, which accounts for the typical gaze- dependent increase of DBN with lateral and downward gaze [5]. Contrary to this concept, we here report about a patient with a confined lesion in the midline medullary brainstem presenting with an inverse eye position dependency: DBN increased with upgaze and decreased with downgaze. This may shed some new light on the impact of floccular afferents, i.e., the paramedian medullary tract (PMT) cells, on the eye position dependency of DBN and it may have some new clinical implications. |
Veronica Whitford; Gillian A. O'Driscoll; Christopher C. Pack; Ridha Joober; Ashok Malla; Debra Titone In: Journal of Experimental Psychology: General, vol. 142, no. 1, pp. 57–75, 2013. @article{Whitford2013, Language and oculomotor disturbances are 2 of the best replicated findings in schizophrenia. However, few studies have examined skilled reading in schizophrenia (e.g., Arnott, Sali, Copland, 2011; Hayes & O'Grady, 2003; Revheim et al., 2006; E. O. Roberts et al., 2012), and none have examined the contribution of cognitive and motor processes that underlie reading performance. Thus, to evaluate the relationship of linguistic processes and oculomotor control to skilled reading in schizophrenia, 20 individuals with schizophrenia and 16 demographically matched controls were tested using a moving window paradigm (McConkie & Rayner, 1975). Linguistic skills supporting reading (phonological awareness) were assessed with the Comprehensive Test of Phonological Processing (R. K. Wagner, Torgesen, & Rashotte, 1999). Eye movements were assessed during reading tasks and during nonlinguistic tasks tapping basic oculomotor control (prosaccades, smooth pursuit) and executive functions (predictive saccades, antisaccades). Compared with controls, schizophrenia patients exhibited robust oculomotor markers of reading difficulty (e.g., reduced forward saccade amplitude) and were less affected by reductions in window size, indicative of reduced perceptual span. Reduced perceptual span in schizophrenia was associated with deficits in phonological processing and reduced saccade amplitudes. Executive functioning (antisaccade errors) was not related to perceptual span but was related to reading comprehension. These findings suggest that deficits in language, oculomotor control, and cognitive control contribute to skilled reading deficits in schizophrenia. Given that both language and oculomotor dysfunction precede illness onset, reading may provide a sensitive window onto cognitive dysfunction in schizophrenia vulnerability and be an important target for cognitive remediation. |
Tracey A. Williams; Melanie A. Porter; Robyn Langdon Viewing social scenes: A visual scan-path study comparing fragile X syndrome and williams syndrome Journal Article In: Journal of Autism and Developmental Disorders, vol. 43, no. 8, pp. 1880–1894, 2013. @article{Williams2013a, Fragile X syndrome (FXS) and Williams syndrome (WS) are both genetic disorders which present with similar cognitive-behavioral problems, but distinct social phenotypes. Despite these social differences both syndromes display poor social relations which may result from abnormal social processing. This study aimed to manipulate the location of socially salient information within scenes to investigate the visual attentional mechanisms of: capture, disengagement, and/or general engagement. Findings revealed that individuals with FXS avoid social information presented centrally, at least initially. The WS findings, on the other hand, provided some evidence that difficulties with attentional disengagement, rather than attentional capture, may play a role in the WS social phenotype. These findings are discussed in relation to the distinct social phenotypes of these two disorders. |
Heather Cleland Woods; Christoph Scheepers; K. A. Ross; Colin A. Espie; Stephany M. Biello What are you looking at? Moving toward an attentional timeline in insomnia: A novel semantic eye tracking study Journal Article In: Sleep, vol. 36, no. 10, pp. 1491–1499, 2013. @article{Woods2013, STUDY OBJECTIVES: To date, cognitive probe paradigms have been used in different guises to obtain reaction time measurements suggestive of an attention bias towards sleep in insomnia. This study adopts a methodology which is novel to sleep research to obtain a continual record of where the eyes-and therefore attention-are being allocated with regard to sleep and neutral stimuli.$backslash$n$backslash$nDESIGN: A head mounted eye tracker (Eyelink II,SR Research, Ontario, Canada) was used to monitor eye movements in respect to two words presented on a computer screen, with one word being a sleep positive, sleep negative, or neutral word above or below a second distracter pseudoword. Probability and reaction times were the outcome measures.$backslash$n$backslash$nPARTICIPANTS: Sleep group classification was determined by screening interview and PSQI (> 8 = insomnia, < 3 = good sleeper) score.$backslash$n$backslash$nMEASUREMENTS AND RESULTS: Those individuals with insomnia took longer to fixate on the target word and remained fixated for less time than the good sleep controls. Word saliency had an effect with longer first fixations on positive and negative sleep words in both sleep groups, with largest effect sizes seen with the insomnia group.$backslash$n$backslash$nCONCLUSIONS: This overall delay in those with insomnia with regard to vigilance and maintaining attention on the target words moves away from previous attention bias work showing a bias towards sleep, particularly negative, stimuli but is suggestive of a neurocognitive deficit in line with recent research. |
Xiao Lin Zhu; Shu Ping Tan; Fu De Yang; Wei Sun; Chong Sheng Song; Jie Feng Cui; Yan Li Zhao; Feng Mei Fan; Ya Jun Li; Yun Long Tan; Yi Zhuang Zou Visual scanning of emotional faces in schizophrenia Journal Article In: Neuroscience Letters, vol. 552, pp. 46–51, 2013. @article{Zhu2013a, This study investigated eye movement differences during facial emotion recognition between 101 patients with chronic schizophrenia and 101 controls. Independent of facial emotion, patients with schizophrenia processed facial information inefficiently; they showed significantly more direct fixations that lasted longer to interest areas (IAs), such as the eyes, nose, mouth, and nasion. The total fixation number, mean fixation duration, and total fixation duration were significantly increased in schizophrenia. Additionally, the number of fixations per second to IAs (IA fixation number/s) was significantly lower in schizophrenia. However, no differences were found between the two groups in the proportion of number of fixations to IAs or total fixation number (IA fixation number %). Interestingly, the negative symptoms of patients with schizophrenia negatively correlated with IA fixation number %. Both groups showed significantly greater attention to positive faces. Compared to controls, patients with schizophrenia exhibited significantly more fixations directed to IAs, a higher total fixation number, and lower IA fixation number/s for negative faces. These results indicate that facial processing efficiency is significantly decreased in schizophrenia, but no difference was observed in processing strategy. Patients with schizophrenia may have special deficits in processing negative faces, and negative symptoms may affect visual scanning parameters. |
Chia-Chien Wu; Eileen Kowler Timing of saccadic eye movements during visual search for multiple targets Journal Article In: Journal of Vision, vol. 13, no. 11, pp. 11–11, 2013. @article{Wu2013, Visual search requires sequences of saccades. Many studies have focused on spatial aspects of saccadic decisions, while relatively few (e.g., Hooge & Erkelens, 1999) consider timing.We studied saccadic timing during search for targets (thin circles containing tilted lines) located among nontargets (thicker circles). Tasks required either (a) estimating the mean tilt of the lines, or (b) looking at targets without a concurrent psychophysical task. The visual similarity of targets and nontargets affected both the probability of hitting a target and the saccade rate in both tasks. Saccadic timing also depended on immediate conditions, specifically, (a) the type of currently fixated location (dwell time was longer on targets than nontargets), (b) the type of goal (dwell time was shorter prior to saccades that hit targets), and (c) the ordinal position of the saccade in the sequence. The results show that timing decisions take into account the difficulty of finding targets, as well as the cost of delays. Timing strategies may be a compromise between the attempt to find and locate targets, or other suitable landing locations, using eccentric vision (at the cost of increased dwell times) versus a strategy of exploring less selectively at a rapid rate. |
Esther X. W. Wu; Syed O. Gilani; Jeroen J. A. Boxtel; Ido Amihai; Fook K. Chua; Shih-Cheng Yen Parallel programming of saccades during natural scene viewing: Evidence from eye movement positions Journal Article In: Journal of Vision, vol. 13, no. 12, pp. 17–17, 2013. @article{Wu2013a, Previous studies have shown that saccade plans during natural scene viewing can be programmed in parallel. This evidence comes mainly from temporal indicators, i.e., fixation durations and latencies. In the current study, we asked whether eye movement positions recorded during scene viewing also reflect parallel programming of saccades. As participants viewed scenes in preparation for a memory task, their inspection of the scene was suddenly disrupted by a transition to another scene. We examined whether saccades after the transition were invariably directed immediately toward the center or were contingent on saccade onset times relative to the transition. The results, which showed a dissociation in eye movement behavior between two groups of saccades after the scene transition, supported the parallel programming account. Saccades with relatively long onset times (>100 ms) after the transition were directed immediately toward the center of the scene, probably to restart scene exploration. Saccades with short onset times (<100 ms) moved to the center only one saccade later. Our data on eye movement positions provide novel evidence of parallel programming of saccades during scene viewing. Additionally, results from the analyses of intersaccadic intervals were also consistent with the parallel programming hypothesis. |
Jing Zhou; Adam Reeves; Scott N. J. Watamaniuk; Stephen J. Heinen Shared attention for smooth pursuit and saccades Journal Article In: Journal of Vision, vol. 13, no. 4, pp. 1–12, 2013. @article{Zhou2013, Identification of brief luminance decrements on parafoveal stimuli presented during smooth pursuit improves when a spot pursuit target is surrounded by a larger random dot cinematogram (RDC) that moves with it (Heinen, Jin, & Watamaniuk, 2011). This was hypothesized to occur because the RDC provided an alternative, less attention-demanding pursuit drive, and therefore released attentional resources for visual perception tasks that are shared with those used to pursue the spot. Here, we used the RDC as a tool to probe whether spot pursuit also shares attentional resources with the saccadic system. To this end, we set out to determine if the RDC could release attention from pursuit of the spot to perform a saccade task. Observers made a saccade to one of four parafoveal targets that moved with the spot pursuit stimulus. The targets either moved alone or were surrounded by an RDC (100% coherence). Saccade latency decreased with the RDC, suggesting that the RDC released attention needed to pursue the spot, which was then used for the saccade task. Additional evidence that attention was released by the RDC was obtained in an experiment in which attention was anchored to the fovea by requiring observers to detect a brief color change applied 130 ms before the saccade target appeared. This manipulation eliminated the RDC advantage. The results imply that attentional resources used by the pursuit and saccadic eye movement control systems are shared. |
Eckart Zimmermann The reference frames in saccade adaptation Journal Article In: Journal of Neurophysiology, vol. 109, pp. 1815, 2013. @article{Zimmermann2013a, Saccade adaptation is a mecha- nism that adjusts saccade landing positions if they systematically fail to reach their intended target. In the laboratory, saccades can be shortened or lengthened if the saccade target is displaced during execution of the saccade. In this study, saccades were performed from different positions to an adapted saccade target to dissociate adapta- tion to a spatiotopic position in external space from a combined retinotopic and spatiotopic coding. The presentation duration of the saccade target before saccade execution was systematically varied, during adaptation and during test trials, with a delayed saccade paradigm. Spatiotopic shifts in landing positions depended on a certain preview duration of the target before saccade execution. When saccades were performed immediately to a suddenly appearing target, no spatiotopic adaptation was observed. These results suggest that a spatiotopic representation of the visual target signal builds up as a function of the duration the saccade target is visible before saccade execution. Different coordinate frames might also explain the separate adaptability of reactive and voluntary saccades. Spatiotopic effects were found only in outward adaptation but not in inward adaptation, which is consistent with the idea that outward adaptation takes place at the level of the visual target representation, whereas inward adap- tation is achieved at a purely motor level. |
Daniel Mirman; Allison E. Britt; Qi Chen Effects of phonological and semantic deficits on facilitative and inhibitory consequences of item repetition in spoken word comprehension Journal Article In: Neuropsychologia, vol. 51, no. 10, pp. 1848–1856, 2013. @article{Mirman2013, Repeating a word can have both facilitative and inhibitory effects on subsequent processing. The present study investigated these dynamics by examining the facilitative and inhibitory consequences of different kinds of item repetition in two individuals with aphasia and a group of neurologically intact control participants. The two individuals with aphasia were matched on overall aphasia severity, but had deficits at different levels of processing: one with a phonological deficit and spared semantic processing, the other with a semantic deficit and spared phonological processing. Participants completed a spoken word-to-picture matching task in which they had to pick which of four object images matched the spoken word. The trials were grouped into pairs such that exactly two objects from the first trial in a pair were present on screen during the second trial in the pair. When the second trial's target was the same as the first trial's target, compared to control participants, both participants with aphasia exhibited equally larger repetition priming effects. When the second trial's target was one of the new items, the participant with a phonological deficit exhibited a significantly more negative effect (i.e., second trial response slower than first trial response) than the control participants and the participant with a semantic deficit. Simulations of a computational model confirmed that this pattern of results could arise from (1) normal residual activation being functionally more significant when overall lexical processing is slower and (2) residual phonological activation of the previous trial's target having a particularly strong inhibitory effect specifically when phonological processing is impaired because the task was phonologically-driven (the spoken input specified the target). These results provide new insights into perseveration errors and lexical access deficits in aphasia. |
Roberta Daini; Andrea Albonico; Manuela Malaspina; Marialuisa Martelli; Silvia Primativo; Lisa S. Arduino Dissociation in optokinetic stimulation sensitivity between omission and substitution reading errors in neglect dyslexia Journal Article In: Frontiers in Human Neuroscience, vol. 7, pp. 581, 2013. @article{Daini2013, Although omission and substitution errors in neglect dyslexia (ND) patients have always been considered as different manifestations of the same acquired reading disorder, recently, we proposed a new dual mechanism model. While omissions are related to the exploratory disorder which characterizes unilateral spatial neglect (USN), substitutions are due to a perceptual integration mechanism. A consequence of this hypothesis is that specific training for omission-type ND patients would aim at restoring the oculo-motor scanning and should not improve reading in substitution-type ND. With this aim we administered an optokinetic stimulation (OKS) to two brain-damaged patients with both USN and ND, MA and EP, who showed ND mainly characterized by omissions and substitutions, respectively. MA also showed an impairment in oculo-motor behavior with a non-reading task, while EP did not. The two patients presented a dissociation with respect to their sensitivity to OKS, so that, as expected, MA was positively affected, while EP was not. Our results confirm a dissociation between the two mechanisms underlying omission and substitution reading errors in ND patients. Moreover, they suggest that such a dissociation could possibly be extended to the effectiveness of rehabilitative procedures, and that patients who mainly omit contralesional-sided letters would benefit from OKS. |
Kirsten A. Dalrymple; Alexander K. Gray; Brielle L. Perler; Elina Birmingham; Walter F. Bischof; Jason J. S. Barton; Alan Kingstone Eyeing the eyes in social scenes: Evidence for top-down control of stimulus selection in simultanagnosia Journal Article In: Cognitive Neuropsychology, vol. 30, no. 1, pp. 25–40, 2013. @article{Dalrymple2013, Simultanagnosia is a disorder of visual attention resulting from bilateral parieto-occipital lesions. Healthy individuals look at eyes to infer people's attentional states, but simultanagnosics allocate abnormally few fixations to eyes in scenes. It is unclear why simultanagnosics fail to fixate eyes, but it might reflect that they are (a) unable to locate and fixate them, or (b) do not prioritize attentional states. We compared eye movements of simultanagnosic G.B. to those of healthy subjects viewing scenes normally or through a restricted window of vision. They described scenes and explicitly inferred attentional states of people in scenes. G.B. and subjects viewing scenes through a restricted window made few fixations on eyes when describing scenes, yet increased fixations on eyes when inferring attention. Thus G.B. understands that eyes are important for inferring attentional states and can exert top-down control to seek out and process the gaze of others when attentional states are of interest. |
C. Hemptinne; Adrian Ivanoiu; Philippe Lefèvre; Marcus Missal How does Parkinson's disease and aging affect temporal expectation and the implicit timing of eye movements? Journal Article In: Neuropsychologia, vol. 51, no. 2, pp. 340–348, 2013. @article{Hemptinne2013, Anticipatory eye movements are often evoked by the temporal expectation of an upcoming event. Temporal expectation is based on implicit timing about when a future event could occur. Implicit timing emerges from observed temporal regularities in a changing stimulus without any voluntary estimate of elapsed time, unlike explicit timing. The neural bases of explicit and implicit timing are likely different. It has been shown that the basal ganglia (BG) play a central role in explicit timing. In order to determine the influence of BG in implicit timing, we investigated the influence of early Parkinson's disease (PD) and aging on the latency of anticipatory eye movements. We hypothesized that a deficit of implicit timing should yield inadequate temporal expectations, and consequently abnormally timed anticipatory eye movements compared with age-matched controls. To test this hypothesis, we used an oculomotor paradigm where anticipation of a salient target event plays a central role. Participants pursued a visual target that moved along a circular path at a constant velocity. After a randomly short (1200. ms) or long (2400. ms) forward path, the target reversed direction, returned to its starting position and stopped. Target motion reversal caused an abrupt 'slip' of the pursued target image on the retina and was a particularly salient event evoking anticipatory eye movements. Anticipatory eye movements were less frequent in PD patients. However, the timing of anticipation of target motion reversal was statistically similar in PD patients and control subjects. Other eye movements showed statistically significant differences between PD and controls, but these differences could be attributed to other factors. We conclude that all anticipatory eye movements are not similarly impaired in PD and that implicit timing of salient events seems largely unaffected by this disease. The results support the hypothesis that implicit and explicit timing are differently affected by BG dysfunction. |
Louis F. Dell'Osso; Jonathan B. Jacobs Normal pursuit-system limitations — first discovered in infantile nystagmus syndrome Journal Article In: Journal of Eye Movement Research, vol. 6, no. 1, pp. 1–24, 2013. @article{DellOsso2013, Infantile nystagmus syndrome (INS) patients occasionally have impaired pursuit. Model and patient data identified relative timing between target motion initiation and INS-waveform saccades as the cause. We used a new stimulus, the “step-pause-ramp” (SPR), to induce saccades proximal to target-velocity onset and test their effect on normal pursuit. Our OMS model predicted that proximal saccades impaired normal ramp responses, as in INS. Eye movements of subjects were calibrated monocularly and recorded binocularly; data were analyzed using OMtools software. Proximal saccades caused lengthened target acquisition times and steady-state position errors, confirming the model's predictions. Spontaneous pursuit oscillation supported the hypothesis that INS is caused by loss of smooth-pursuit damping. Snooth pursuit may be impaired by saccades overlapping targetmotion onset. |
Virginie Desestret; Nathalie Streichenberger; Muriel T. N. Panouillères; Denis Pélisson; B. Plus; Charles Duyckaerts; Dennis K. Burns; Christian Scheiber; Alain Vighetto; Caroline Tilikete An elderly woman with difficulty reading and abnormal eye movements Journal Article In: Journal of Neuro-Ophthalmology, vol. 33, no. 3, pp. 296–301, 2013. @article{Desestret2013, A 73-year-old woman was evaluated in our neuro- ophthalmology clinic with a 1-year history of progressive difficulty reading. The patient's visual acuity, pupillary reactions to light and near stimulation, visual fields, and fundi were normal. Examination of her eye movements revealed a supranuclear vertical gaze abnormality, charac- terized by lack of upward saccades but intact downward saccades. The patient also had had difficulty initiating voluntary, especially leftward horizontal saccades on command, but reactive horizontal saccades were relatively well preserved. She was able to follow a pencil light moved by the examiner using small saccades (saccadic smooth pursuit) and her vestibulo-ocular reflex (VOR) was intact. She had apraxia of lid closure. The patient had no cognitive deficit, behavioral or social disturbance, aphasia, alexia, limb apraxia, postural ataxia, pyramidal signsorparkinsonism. |
Jose Ignacio Egaña; Christ Devia; Rocío Mayol; Javiera Parrini; Gricel Orellana; Aida Ruiz; Pedro E. Maldonado Small saccades and image complexity during free viewing of natural images in schizophrenia Journal Article In: Frontiers in Psychiatry, vol. 4, pp. 37, 2013. @article{Egana2013, In schizophrenia, patients display dysfunctions during the execution of simple visual tasks such as antisaccade or smooth pursuit. In more ecological scenarios, such as free viewing of natural images, patients appear to make fewer and longer visual fixations and display shorter scanpaths. It is not clear whether these measurements reflect alterations in their proficiency to perform basic eye movements, such as saccades and fixations, or are related to high-level mechanisms, such as exploration or attention. We utilized free exploration of natural images of different complexities as a model of an ecological context where normally operative mechanisms of visual control can be accurately measured. We quantified visual exploration as Euclidean distance, scanpaths, saccades, and visual fixation, using the standard SR-Research eye tracker algorithm (SR). We then compared this result with a computation that includes microsaccades (EM). We evaluated eight schizophrenia patients and corresponding healthy controls (HC). Next, we tested whether the decrement in the number of saccades and fixations, as well as their increment in duration reported previously in schizophrenia patients, resulted from the increasing occurrence of undetected microsaccades. We found that when utilizing the standard SR algorithm, patients displayed shorter scanpaths as well as fewer and shorter saccades and fixations. When we employed the EM algorithm, the differences in these parameters between patients and HC were no longer significant. On the other hand, we found that image complexity plays an important role in exploratory behaviors, demonstrating that this factor explains most of differences between eye-movement behaviors in schizophrenia patients. These results help elucidate the mechanisms of visual motor control that are affected in schizophrenia and contribute to the finding of adequate markers for diagnosis and treatment for this condition. |
Joost Felius; Zainab A. Muhanna Visual deprivation and foveation characteristics both underlie visual acuity deficits in idiopathic infantile nystagmus Journal Article In: Investigative Ophthalmology & Visual Science, vol. 54, no. 5, pp. 3520–3525, 2013. @article{Felius2013, PURPOSE. Children with idiopathic infantile nystagmus (IIN) exhibit visual acuity deficits that have been modeled in terms of foveation characteristics of the nystagmus waveform. Here we present evidence for an additional component of acuity loss associated with the deprivation experienced during the sensitive period of visual development. METHODS. Binocular grating visual acuity and eye movement recordings were obtained from 56 children with IIN (age 4.8 6 3.2 years) and documented waveform history from longitudinal visits. Visual acuity was modeled in terms of foveation characteristics (Nystagmus Optimal Fixation Function, NOFF) and of each child's time course of pendular nystagmus during the sensitive period. RESULTS. Mean visual acuity was 0.25 6 0.19 logMAR below age norms, and the mean foveation fraction was 0.28 (NOFF ¼?0.9 6 2.3 logits). Nystagmus had a median onset at age 3 months and transitioned to waveforms with extended foveation at age 35 months. The best fit of the model showed the following: Poor foveation (0.01 foveation fraction) was associated with 0.60 logMAR acuity deficit; this deficit gradually reduced to zero for increasingly better foveation; pendular nystagmus during each decile of the sensitive period was associated with an additional 0.022 logMAR deficit. The model accounted for 57% of the variance in visual acuity and provided a better fit than either component alone. CONCLUSIONS. Visual acuity in IIN is explained better if, besides the child's foveation characteristics, an additional component is taken into account representing the nystagmus- induced visual deprivation during the sensitive period. These findings may have implications for the timing of treatment decisions in children with IIN. |
Gerardo Fernández; Pablo Mandolesi; Nora P. Rotstein; Oscar Colombo; Osvaldo Agamennoni; Luis E. Politi Eye movement alterations during reading in patients with early Alzheimer disease Journal Article In: Investigative Ophthalmology & Visual Science, vol. 54, no. 13, pp. 8345–8352, 2013. @article{Fernandez2013, Purpose: Eye movements follow a reproducible pattern during normal reading. Each eye movement ends up in a fixation point, which allows the brain to process the incoming information and to program the following saccade. Alzheimer disease (AD) produces eye movement abnormalities and disturbances in reading. In this work we investigated whether eye movement alterations during reading might be already present at very early stages of the disease. Methods: Twenty female and male adult patients with the diagnosis of probable AD and 20 age-matching individuals with no evidence of cognitive decline participated in the study. Participants were seated in front of a 20-inch LCD monitor and single sentences were presented on it. Eye movements were recorded with an eyetracker, with a sampling rate of 1000 Hz and an eye position resolution of 20-s arc. Results: Analysis of eye movements during reading revealed that patients with early AD decreased the amount of single fixations, increased their total number of first and second pass fixations, the amount of saccade regressions and the number of words skipped, compared with healthy individuals (controls). They also reduced the size of outgoing saccades, simultaneously increasing fixation duration. Conclusions: The present study shows that patients with mild AD evidenced marked alterations in eye movement behavior during reading, even at early stages of the disease. Hence, evaluation of eye movement behavior during reading might provide a useful tool for a more precise early diagnosis of AD and for dynamical monitoring of the pathology. |
Lore Thaler; Alexander C. Schütz; Melvyn A. Goodale; Karl R. Gegenfurtner What is the best fixation target? The effect of target shape on stability of fixational eye movements Journal Article In: Vision Research, vol. 76, pp. 31–42, 2013. @article{Thaler2013, People can direct their gaze at a visual target for extended periods of time. Yet, even during fixation the eyes make small, involuntary movements (e.g. tremor, drift, and microsaccades). This can be a problem during experiments that require stable fixation. The shape of a fixation target can be easily manipulated in the context of many experimental paradigms. Thus, from a purely methodological point of view, it would be good to know if there was a particular shape of a fixation target that minimizes involuntary eye movements during fixation, because this shape could then be used in experiments that require stable fixation. Based on this methodological motivation, the current experiments tested if the shape of a fixation target can be used to reduce eye movements during fixation. In two separate experiments subjects directed their gaze at a fixation target for 17. s on each trial. The shape of the fixation target varied from trial to trial and was drawn from a set of seven shapes, the use of which has been frequently reported in the literature. To determine stability of fixation we computed spatial dispersion and microsaccade rate. We found that only a target shape which looks like a combination of bulls eye and cross hair resulted in combined low dispersion and microsaccade rate. We recommend the combination of bulls eye and cross hair as fixation target shape for experiments that require stable fixation. |
Hiroshi Ueda; Kohske Takahashi; Katsumi Watanabe Contributions of retinal input and phenomenal representation of a fixation object to the saccadic gap effect Journal Article In: Vision Research, vol. 82, pp. 52–57, 2013. @article{Ueda2013, The saccadic " gap effect" refers to a phenomenon whereby saccadic reaction times (SRTs) are shortened by the removal of a visual fixation stimulus prior to target presentation. In the current study, we investigated whether the gap effect was influenced by retinal input of a fixation stimulus, as well as phenomenal permanence and/or expectation of the re-emergence of a fixation stimulus. In Experiment 1, we used an occluded fixation stimulus that was gradually hidden by a moving plate prior to the target presentation, which produced the impression that the fixation stimulus still remained and would reappear from behind the plate. We found that the gap effect was significantly weakened with the occluded fixation stimulus. However, the SRT with the occluded fixation stimulus was still shorter in comparison to when the fixation stimulus physically remained on the screen. In Experiment 2, we investigated whether this effect was due to phenomenal maintenance or expectation of the reappearance of the fixation stimulus; this was achieved by using occluding plates that were an identical color to the background screen, giving the impression of reappearance of the fixation stimulus but not of its maintenance. The result showed that the gap effect was still weakened by the same degree even without phenomenal maintenance of the fixation stimulus. These results suggest that the saccadic gap effect is modulated by both retinal input and subjective expectation of re-emergence of the fixation stimulus. In addition to oculomotor mechanisms, other components, such as attentional mechanisms, likely contribute to facilitation of the subsequent action. |
Matteo Valsecchi; Karl R. Gegenfurtner; Alexander C. Schutz Saccadic and smooth-pursuit eye movements during reading of drifting texts Journal Article In: Journal of Vision, vol. 13, no. 10, pp. 8–8, 2013. @article{Valsecchi2013a, Reading is a complex visuomotor behavior characterized by an alternation of fixations and saccadic eye movements. Despite the widespread use of drifting texts in various settings, very little is known about eye movements under these conditions. Here we investigated oculomotor behavior during reading of texts which were drifting horizontally or vertically at different speeds. Consistent with previous reports, drifting texts were read by an alternation of smooth-pursuit and saccadic eye movements. Detailed analysis revealed several interactions between smooth pursuit and saccades. On one side, the gain of smooth pursuit was increased after the execution of a saccade. On the other side, the peak velocity of saccades was reduced for the horizontally drifting text, in which saccades and pursuit were executed in opposite directions. In addition, we show that well-known findings from the reading of static texts extend to drifting text, such as the preferred viewing location, the inverted optimal viewing position, and the correlation between saccade amplitude and subsequent pursuit/fixation duration. In general, individual eye-movement parameters such as saccade amplitude and fixation/pursuit durations were correlated across self-paced reading of static text and time-constrained reading of static and drifting texts. These results show that findings from basic oculomotor research also apply to the reading of drifting texts. Similarly, basic reading principles apply to the reading of static and drifting texts in a similar way. This exemplifies the reading of drifting text as a visuomotor behavior which is influenced by low-level eye-movement control as well as by cognitive and linguistic processing. |
Stefan Van der Stigchel; Tanja C. W. Nijboer How global is the global effect? The spatial characteristics of saccade averaging Journal Article In: Vision Research, vol. 84, pp. 6–15, 2013. @article{VanderStigchel2013c, When a target and a distractor are presented in close proximity, an eye movement will generally land in between these two elements. This is known as the 'global effect' and has been claimed to be a reflection of the averaged saccade programs towards both locations. The aim of the present study was to systematically investigate whether there is only a limited area in the saccade map in which saccade averaging occurs. To this end, we examined various distances between target and distractor in two experiments and investigated whether the majority of eye movements landed in between the target and the distractor. Results indicated that the endpoint distribution was unimodal for distances up to 35° (in polar coordinates), with saccades generally landing in between the target and the distractor. When the distance was higher than 45°, the saccade endpoint distribution was predominantly bimodal, with saccades landing either on the target or on the distractor. The decrease in saccade averaging was linear until almost no averaging saccades were observed for the longest distances. As saccades landing in between target and distractor reflect a weak, or absent, top-down signal, the present study indicated that top-down information is unable to strongly influence the oculomotor system when target and distractor are presented in close proximity. In this situation, the resulting eye movement is determined by the weighted average of saccade vectors present in a restricted region in the motor map. |
Nathalie Van Humbeeck; Nadine Schmitt; Frouke Hermens; Johan Wagemans; Udo A. Ernst The role of eye movements in a contour detection task Journal Article In: Journal of Vision, vol. 13, no. 14, pp. 5, 2013. @article{VanHumbeeck2013, Vision combines local feature integration with active viewing processes, such as eye movements, to perceive complex visual scenes. However, it is still unclear how these processes interact and support each other. Here, we investigated how the dynamics of saccadic eye movements interact with contour integration, focusing on situations in which contours are difficult to find or even absent. We recorded observers' eye movements while they searched for a contour embedded in a background of randomly oriented elements. Task difficulty was manipulated by varying the contour's path angle. An association field model of contour integration was employed to predict potential saccade targets by identifying stimulus locations with high contour salience. We found that the number and duration of fixations increased with the increasing path angle of the contour. In addition, fixation duration increased over the course of a trial, and the time course of saccade amplitude depended on the percept of observers. Model fitting revealed that saccades fully compensate for the reduced saliency of peripheral contour targets. Importantly, our model predicted fixation locations to a considerable degree, indicating that observers fixated collinear elements. These results show that contour integration actively guides eye movements and determines their spatial and temporal parameters. |
Robin Walker; Valerie Benson Remote distractor effects and saccadic inhibition: Spatial and temporal modulation Journal Article In: Journal of vision, vol. 13, no. 11, pp. 1–21, 2013. @article{Walker2013a, The onset of a visual distractor remote from a saccade target is known to increase saccade latency (the remote distractor effect [RDE]). In addition, distractors may also selectively inhibit saccades that would be initiated about 90 ms after distractor onset (termed saccadic inhibition [SI]). Recently, it has been proposed that the transitory inhibition of saccades (SI) may underlie the increase in mean latency (RDE). In a first experiment, the distractor eccentricity was manipulated, and a robust RDE that was strongly modulated by distractor eccentricity was observed. However, the underlying latency distributions did not reveal clear evidence of SI. A second experiment manipulated distractor spatial location and the timing of the distractor onset in relation to the target. An RDE was again observed with remote distractors away from the target axis and under conditions with early-onset distractors that would be unlikely to produce SI, whereas later distractor onsets produced an RDE along with some evidence of an SI effect. A third experiment using a mixed block of target-distractor stimulus-onset asynchronies (SOAs) revealed an RDE that varied with both distractor eccentricity and SOA and changes to latency distributions consistent with the timing of SI. We argue that the notion that SI underpins the RDE is similar to the earlier argument that express saccades underlie the fixation offset (gap) effect and that changes in mean latency and to the shape of the underlying latency distributions following a visual onset may involve more than one inhibitory process. |
Alex L. White; Martin Rolfs; Marisa Carrasco Adaptive deployment of spatial and feature-based attention before saccades Journal Article In: Vision Research, vol. 85, pp. 26–35, 2013. @article{White2013, What you see depends not only on where you are looking but also on where you will look next. The pre-saccadic attention shift is an automatic enhancement of visual sensitivity at the target of the next saccade. We investigated whether and how perceptual factors independent of the oculomotor plan modulate pre-saccadic attention within and across trials. Observers made saccades to one (the target) of six patches of moving dots and discriminated a brief luminance pulse (the probe) that appeared at an unpredictable location. Sensitivity to the probe was always higher at the target's location (spatial attention), and this attention effect was stronger if the previous probe appeared at the previous target's location. Furthermore, sensitivity was higher for probes moving in directions similar to the target's direction (feature-based attention), but only when the previous probe moved in the same direction as the previous target. Therefore, implicit cognitive processes permeate pre-saccadic attention, so that-contingent on recent experience-it flexibly distributes resources to potentially relevant locations and features. |
Niklas Wilming; Simon Harst; Nico Schmidt; Peter König Saccadic momentum and facilitation of return saccades contribute to an optimal foraging strategy Journal Article In: PLoS Computational Biology, vol. 9, no. 1, pp. e1002871, 2013. @article{Wilming2013, The interest in saccadic IOR is funneled by the hypothesis that it serves a clear functional purpose in the selection of fixation points: the facilitation of foraging. In this study, we arrive at a different interpretation of saccadic IOR. First, we find that return saccades are performed much more often than expected from the statistical properties of saccades and saccade pairs. Second, we find that fixation durations before a saccade are modulated by the relative angle of the saccade, but return saccades show no sign of an additional temporal inhibition. Thus, we do not find temporal saccadic inhibition of return. Interestingly, we find that return locations are more salient, according to empirically measured saliency (locations that are fixated by many observers) as well as stimulus dependent saliency (defined by image features), than regular fixation locations. These results and the finding that return saccades increase the match of individual trajectories with a grand total priority map evidences the return saccades being part of a fixation selection strategy that trades off exploration and exploitation. |
Jorge Otero-Millan; Rosalyn Schneider; R. John Leigh; Stephen L. Macknik; Susana Martinez-Conde Saccades during attempted fixation in Parkinsonian disorders and recessive ataxia: From microsaccades to square-wave jerks Journal Article In: PLoS ONE, vol. 8, no. 3, pp. e58535, 2013. @article{OteroMillan2013a, During attempted visual fixation, saccades of a range of sizes occur. These "fixational saccades" include microsaccades, which are not apparent in regular clinical tests, and "saccadic intrusions", predominantly horizontal saccades that interrupt accurate fixation. Square-wave jerks (SWJs), the most common type of saccadic intrusion, consist of an initial saccade away from the target followed, after a short delay, by a "return saccade" that brings the eye back onto target. SWJs are present in most human subjects, but are prominent by their increased frequency and size in certain parkinsonian disorders and in recessive, hereditary spinocerebellar ataxias. Here we asked whether fixational saccades showed distinctive features in various parkinsonian disorders and in recessive ataxia. Although some saccadic properties differed between patient groups, in all conditions larger saccades were more likely to form SWJs, and the intervals between the first and second saccade of SWJs were similar. These findings support the proposal of a common oculomotor mechanism that generates all fixational saccades, including microsaccades and SWJs. The same mechanism also explains how the return saccade in SWJs is triggered by the position error that occurs when the first saccadic component is large, both in the healthy brain and in neurological disease. |
Irene Ablinger; Walter Huber; Kerstin I. Schattka; Ralph Radach Recovery in a letter-by-letter reader: More efficiency at the expense of normal reading strategy Journal Article In: Neurocase, vol. 19, no. 3, pp. 236–255, 2013. @article{Ablinger2013, Although changes in reading performance of recovering letter-by-letter readers have been described in some detail, no prior research has provided an in-depth analysis of the underlying adaptive word processing strategies. Our work examined the reading performance of a letter-by-letter reader, FH, over a period of 15 months, using eye movement methodology to delineate the recovery process at two different time points (T1, T2). A central question is whether recovery is characterized either by moving back towards normal word processing or by refinement and possibly automatization of an existing pathological strategy that was developed in response to the impairment. More specifically, we hypothesized that letter-by-letter reading may be executed with at least four different strategies and our work sought to distinguish between these alternatives. During recovery significant improvements in reading performance were achieved. A shift of fixation positions from the far left to the extreme right of target words was combined with many small and very few longer regressive saccades. Apparently, ‘letter-by-letter reading' took the form of local clustering, most likely corresponding to the formation ofsublexical units ofanalysis. This pattern was more pronounced at T2, suggesting that improvements in reading efficiency may come at the expense of making it harder to eventually return to normal reading. |
Robert Adam; Alexander P. Leff; Nihal Sinha; Christopher Turner; Paul Bays; Bogdan Draganski; Masud Husain Dopamine reverses reward insensitivity in apathy following globus pallidus lesions Journal Article In: Cortex, vol. 49, no. 5, pp. 1292–1303, 2013. @article{Adam2013, Apathy is a complex, behavioural disorder associated with reduced spontaneous initiation of actions. Although present in mild forms in some healthy people, it is a pathological state in conditions such as Alzheimer's and Parkinson's disease where it can have profoundly devastating effects. Understanding the mechanisms underlying apathy is therefore of urgent concern but this has proven difficult because widespread brain changes in neurodegenerative diseases make interpretation difficult and there is no good animal model.Here we present a very rare case with profound apathy following bilateral, focal lesions of the basal ganglia, with globus pallidus regions that connect with orbitofrontal (OFC) and ventromedial prefrontal cortex (VMPFC) particularly affected. Using two measures of oculomotor decision-making we show that apathy in this individual was associated with reward insensitivity. However, reward sensitivity could be established partially with levodopa and more effectively with a dopamine receptor agonist. Concomitantly, there was an improvement in the patient's clinical state, with reduced apathy, greater motivation and increased social interactions. These findings provide a model system to study a key neuropsychiatric disorder. They demonstrate that reward insensitivity associated with basal ganglia dysfunction might be an important component of apathy that can be reversed by dopaminergic modulation. |
Cordelia D. Aitkin; Elio M. Santos; Eileen Kowler Anticipatory smooth eye movements in autism spectrum disorder Journal Article In: PLoS ONE, vol. 8, no. 12, pp. e83230, 2013. @article{Aitkin2013, Smooth pursuit eye movements are important for vision because they maintain the line of sight on targets that move smoothly within the visual field. Smooth pursuit is driven by neural representations of motion, including a surprisingly strong influence of high-level signals representing expected motion. We studied anticipatory smooth eye movements (defined as smooth eye movements in the direction of expected future motion) produced by salient visual cues in a group of high-functioning observers with Autism Spectrum Disorder (ASD), a condition that has been associated with difficulties in either generating predictions, or translating predictions into effective motor commands. Eye movements were recorded while participants pursued the motion of a disc that moved within an outline drawing of an inverted Y-shaped tube. The cue to the motion path was a visual barrier that blocked the untraveled branch (right or left) of the tube. ASD participants showed strong anticipatory smooth eye movements whose velocity was the same as that of a group of neurotypical participants. Anticipatory smooth eye movements appeared on the very first cued trial, indicating that trial-by-trial learning was not responsible for the responses. These results are significant because they show that anticipatory capacities are intact in high-functioning ASD in cases where the cue to the motion path is highly salient and unambiguous. Once the ability to generate anticipatory pursuit is demonstrated, the study of the anticipatory responses with a variety of types of cues provides a window into the perceptual or cognitive processes that underlie the interpretation of events in natural environments or social situations. |
Neil K. Archibald; Samuel B. Hutton; Michael P. Clarke; Urs P. Mosimann; David J. Burn Visual exploration in Parkinson's disease and Parkinson's disease dementia Journal Article In: Brain, vol. 136, no. 3, pp. 739–750, 2013. @article{Archibald2013, Parkinson's disease, typically thought of as a movement disorder, is increasingly recognized as causing cognitive impairment and dementia. Eye movement abnormalities are also described, including impairment of rapid eye movements (saccades) and the fixations interspersed between them. Such movements are under the influence of cortical and subcortical networks commonly targeted by the neurodegeneration seen in Parkinson's disease and, as such, may provide a marker for cognitive decline. This study examined the error rates and visual exploration strategies of subjects with Parkinson's disease, with and without cognitive impairment, whilst performing a battery of visuo-cognitive tasks. Error rates were significantly higher in those Parkinson's disease groups with either mild cognitive impairment (P = 0.001) or dementia (P < 0.001), than in cognitively normal subjects with Parkinson's disease. When compared with cognitively normal subjects with Parkinson's disease, exploration strategy, as measured by a number of eye tracking variables, was least efficient in the dementia group but was also affected in those subjects with Parkinson's disease with mild cognitive impairment. When compared with control subjects and cognitively normal subjects with Parkinson's disease, saccade amplitudes were significantly reduced in the groups with mild cognitive impairment or dementia. Fixation duration was longer in all Parkinson's disease groups compared with healthy control subjects but was longest for cognitively impaired Parkinson's disease groups. The strongest predictor of average fixation duration was disease severity. Analysing only data from the most complex task, with the highest error rates, both cognitive impairment and disease severity contributed to a predictive model for fixation duration F(2,76) = 12.52, P 0.001, but medication dose did not (r = 0.18 |
Stephen P. Badham; Claire V. Hutchinson Characterising eye movement dysfunction in myalgic encephalomyelitis/ chronic fatigue syndrome Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 251, no. 12, pp. 2769–2776, 2013. @article{Badham2013, BACKGROUND: People who suffer from myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often report that their eye movements are sluggish and that they have difficulties tracking moving objects. However, descriptions of these visual problems are based solely on patients' self-reports of their subjective visual experiences, and there is a distinct lack of empirical evidence to objectively verify their claims. This paper presents the first experimental research to objectively examine eye movements in those suffering from ME/CFS. METHODS: Patients were assessed for ME/CFS symptoms and were compared to age, gender, and education matched controls for their ability to generate saccades and smooth pursuit eye movements. RESULTS: Patients and controls exhibited similar error rates and saccade latencies (response times) on prosaccade and antisaccade tasks. Patients showed relatively intact ability to accurately fixate the target (prosaccades), but were impaired when required to focus accurately in a specific position opposite the target (antisaccades). Patients were most markedly impaired when required to direct their gaze as closely as possible to a smoothly moving target (smooth pursuit). CONCLUSIONS: It is hypothesised that the effects of ME/CFS can be overcome briefly for completion of saccades, but that continuous pursuit activity (accurately tracking a moving object), even for a short time period, highlights dysfunctional eye movement behaviour in ME/CFS patients. Future smooth pursuit research may elucidate and improve diagnosis of ME/CFS. |
Daniela Balslev; Bartholomäus Odoj; Hans-Otto Karnath Role of somatosensory cortex in visuospatial attention Journal Article In: Journal of Neuroscience, vol. 33, no. 46, pp. 18311–18318, 2013. @article{Balslev2013, The human somatosensory cortex (S1) is not among the brain areas usually associated with visuospatial attention. However, such a function can be presumed, given the recently identified eye proprioceptive input to S1 and the established links between gaze and attention. Here we investigated a rare patient with a focal lesion of the right postcentral gyrus that interferes with the processing of eye proprioception without affecting the ability to locate visual objects relative to her body or to execute eye movements. As a behavioral measure of spatial attention, we recorded fixation time during visual search and reaction time for visual discrimination in lateral displays. In contrast to a group of age-matched controls, the patient showed a gradient in looking time and in visual sensitivity toward the midline. Because an attention bias in the opposite direction, toward the ipsilesional space, occurs in patients with spatial neglect, in a second study, we asked whether the incidental coinjury of S1 together with the neglect-typical perisylvian lesion leads to a milder neglect. A voxelwise lesion behavior mapping analysis of a group of right-hemisphere stroke patients supported this hypothesis. The effect of an isolated S1 lesion on visual exploration and visual sensitivity as well as the modulatory role of S1 in spatial neglect suggest a role of this area in visuospatial attention. We hypothesize that the proprioceptive gaze signal in S1, although playing only a minor role in locating visual objects relative to the body, affects the allocation of attention in the visual space. |
Niraj Barot; Rebecca J. McLean; Irene Gottlob; Frank A. Proudlock Reading performance in infantile nystagmus Journal Article In: Ophthalmology, vol. 120, no. 6, pp. 1232–1238, 2013. @article{Barot2013, Objective: To characterize reading deficits in infantile nystagmus (IN), to determine optimal font sizes for reading in IN, and to investigate whether visual acuity (VA) and severity of nystagmus are good indicators of reading performance in IN. Design: Prospective cross-sectional study. Participants and Controls: Seventy-one participants with IN (37 idiopathic, 34 with albinism) and 20 age-matched controls. Methods: Reading performance was assessed using Radner reading charts and was compared with near logarithm of the minimum angle of resolution (logMAR) VA, nystagmus intensity, and foveation characteristics as quantified using eye movement recordings. Main Outcome Measures: Reading acuity (smallest readable font size), maximum reading speed, critical print size (font size below which reading is suboptimal), near logMAR VA, nystagmus intensity, and foveation characteristics (using the eXpanded Nystagmus Acuity Function). Results: Using optimal reading conditions, maximum reading speeds were 18.8% slower in albinism and 14.7% slower in idiopathic IN patients compared with controls. Reading acuities were significantly worse (P<0.001) in IN patients compared with controls. Also, the range of font sizes over which reading speeds were less than the optimum were much larger in IN patients compared with controls (P<0.001). Reading acuity was correlated strongly to near VA (r2= 0.74 albinism |
Ian G. M. Cameron; Donald C. Brien; Kira Links; Sarah Robichaud; Jennifer D. Ryan; Douglas P. Munoz; Tiffany W. Chow Changes to saccade behaviors in parkinson's disease following dancing and observation of dancing Journal Article In: Frontiers in Neurology, vol. 4, pp. 22, 2013. @article{Cameron2013, BACKGROUND: The traditional view of Parkinson's disease (PD) as a motor disorder only treated by dopaminergic medications is now shifting to include non-pharmacologic interventions. We have noticed that patients with PD obtain an immediate, short-lasting benefit to mobility by the end of a dance class, suggesting some mechanism by which dancing reduces bradykinetic symptoms. We have also found that patients with PD are unimpaired at initiating highly automatic eye movements to visual stimuli (pro-saccades) but are impaired at generating willful eye movements away from visual stimuli (anti-saccades). We hypothesized that the mechanisms by which a dance class improves movement initiation may generalize to the brain networks impacted in PD (frontal lobe and basal ganglia, BG), and thus could be assessed objectively by measuring eye movements, which rely on the same neural circuitry. METHODS: Participants with PD performed pro- and anti-saccades before, and after, a dance class. "Before" and "after" saccade performance measurements were compared. These measurements were then contrasted with a control condition (observing a dance class in a video), and with older and younger adult populations, who rested for an hour between measurements. RESULTS: We found an improvement in anti-saccade performance following the observation of dance (but not following dancing), but we found a detriment in pro-saccade performance following dancing. CONCLUSION: We suggest that observation of dance induced plasticity changes in frontal-BG networks that are important for executive control. Dancing, in contrast, increased voluntary movement signals that benefited mobility, but interfered with the automaticity of efficient pro-saccade execution. |
Alexander Pastukhov; Victoria Vonau; Solveiga Stonkute; Jochen Braun Spatial and temporal attention revealed by microsaccades Journal Article In: Vision Research, vol. 85, pp. 45–57, 2013. @article{Pastukhov2013, We compared the spatial and temporal allocation of attention as revealed by microsaccades. Observers viewed several concurrent "rapid serial visual presentation" (RSVP) streams in the periphery while maintaining fixation. They continually attended to, and discriminated targets in one particular, cued stream. Over and above this continuous allocation, spatial attention transients ("attention shifts") were prompted by changes in the cued stream location and temporal attention transients ("attentional blinks") by successful target discriminations. Note that the RSVP paradigm avoided the preparatory suppression of microsaccades in anticipation of stimulus or task events, which had been prominent in earlier studies. Both stream changes and target discriminations evoked residual modulations of microsaccade rate and direction, which were consistent with the presumed attentional dynamics in each case (i.e., attention shift and attentional blink, respectively). Interestingly, even microsaccades associated with neither stream change nor target discrimination reflected the continuous allocation of attention, inasmuch as their direction was aligned with the meridian of the target stream. We conclude that attentional allocation shapes microsaccadic activity continuously, not merely during dynamic episodes such as attentional shifts or blinks. |
Laura Pérez Zapata; J. A. Aznar-Casanova; H. Supèr Two stages of programming eye gaze shifts in 3-D space Journal Article In: Vision Research, vol. 86, pp. 15–26, 2013. @article{PerezZapata2013, Accurate saccadic and vergence eye movements towards selected visual targets are fundamental to perceive the 3-D environment. Despite this importance, shifts in eye gaze are not always perfect given that they are frequently followed by small corrective eye movements. The oculomotor system receives dis- tinct information from various visual cues that may cause incongruity in the planning of a gaze shift. To test this idea, we analyzed eye movements in humans performing a saccade task in a 3-D setting. We show that saccades and vergence movements towards peripheral targets are guided by monocular (perceptual) cues. Approximately 200 ms after the start of fixation at the perceived target, a fixational saccade corrected the eye positions to the physical target location. Our findings suggest that shifts in eye gaze occur in two phases; a large eye movement toward the perceived target location followed by a corrective saccade that directs the eyes to the physical target location. |
Sotiris Plainis; Dionysia Petratou; Trisevgeni Giannakopoulou; Hema Radhakrishnan; Ioannis G. Pallikaris; W. Neil Charman Interocular differences in visual latency induced by reduced-aperture monovision Journal Article In: Ophthalmic and Physiological Optics, vol. 33, no. 2, pp. 123–129, 2013. @article{Plainis2013, PURPOSE: To explore the interocular differences in the temporal responses of the eyes induced by the monocular use of small-aperture optics designed to aid presbyopes by increasing their depth-of-focus. METHODS: Monocular and binocular pattern-reversal visual evoked potentials (VEPs) were measured at a mean photopic field luminance of 30 cd/m(2) in seven normal subjects with either natural pupils or when the non-dominant eye wore a small-aperture contact lens (aperture diameter 1.5, 2.5 or 3.5 mm, or an annular opaque stop of inner and outer diameters 1.5 and 4.0 mm respectively). Responses were also measured with varying stimulus luminance (5, 13.9, 27.2 and 45 cd/m(2)) and a fixed 3.0 mm artificial pupil. RESULTS: Mean natural pupil diameters were 4.7 and 4.4 mm under monocular and binocular conditions respectively. The small-aperture contact lenses reduced the amplitude of the P100 component of the VEP and increased its latency. Inter-ocular differences in latency rose to about 20-25 ms when the pupil diameter of the non-dominant eye was reduced to 1.5 mm. The measurements with fixed pupil and varying luminance suggested that the observed effects were explicable in terms of the changes in retinal illuminance produced by the restrictions in pupil area. CONCLUSIONS: The anisocoria induced by small-aperture approaches to aid presbyopes produces marked interocular differences in visual latency. The literature of the Pulfrich effect suggests that such differences can lead to distortions in the perception of relative movement and, in some cases, to possible hazard. |
Sotiris Plainis; Dionysia Petratou; Trisevgeni Giannakopoulou; Hema Radhakrishnan; Ioannis G. Pallikaris; W. Neil Charman Small-aperture monovision and the Pulfrich experience: Absence of neural adaptation effects Journal Article In: PLoS ONE, vol. 8, no. 10, pp. e75987, 2013. @article{Plainis2013a, PURPOSE: To explore whether adaptation reduces the interocular visual latency differences and the induced Pulfrich effect caused by the anisocoria implicit in small-aperture monovision. METHODS: Anisocoric vision was simulated in two adults by wearing in the non-dominant eye for 7 successive days, while awake, an opaque soft contact lens (CL) with a small, central, circular aperture. This was repeated with aperture diameters of 1.5 and 2.5 mm. Each day, monocular and binocular pattern-reversal Visual Evoked Potentials (VEP) were recorded. Additionally, the Pulfrich effect was measured: the task of the subject was to state whether a a 2-deg spot appeared in front or behind the plane of a central cross when moved left-to-right or right-to-left on a display screen. The retinal illuminance of the dominant eye was varied using neutral density (ND) filters to establish the ND value which eliminated the Pulfrich effect for each lens. All experiments were performed at luminance levels of 5 and 30 cd/m(2). RESULTS: Interocular differences in monocular VEP latency (at 30 cd/m(2)) rose to about 12-15 ms and 20-25 ms when the CL aperture was 2.5 and 1.5 mm, respectively. The effect was more pronounced at 5 cd/m(2) (i.e. with larger natural pupils). A strong Pulfrich effect was observed under all conditions, with the effect being less striking for the 2.5 mm aperture. No neural adaptation appeared to occur: neither the interocular differences in VEP latency nor the ND value required to null the Pulfrich effect reduced over each 7-day period of anisocoric vision. CONCLUSIONS: Small-aperture monovision produced marked interocular differences in visual latency and a Pulfrich experience. These were not reduced by adaptation, perhaps because the natural pupil diameter of the dominant eye was continually changing throughout the day due to varying illumination and other factors, making adaptation difficult. |
Anne Schmechtig; Jane Lees; Lois Grayson; Kevin J. Craig; Rukiya Dadhiwala; Gerard R. Dawson; J. F. William Deakin; Colin T. Dourish; Ivan Koychev; Katrina McMullen; Ellen M. Migo; Charlotte Perry; Lawrence Wilkinson; Robin Morris; Steve C. R. Williams; Ulrich Ettinger Effects of risperidone, amisulpride and nicotine on eye movement control and their modulation by schizotypy Journal Article In: Psychopharmacology, vol. 227, no. 2, pp. 331–345, 2013. @article{Schmechtig2013a, RATIONALE: The increasing demand to develop more efficient compounds to treat cognitive impairments in schizophrenia has led to the development of experimental model systems. One such model system combines the study of surrogate populations expressing high levels of schizotypy with oculomotor biomarkers. OBJECTIVES: We aimed (1) to replicate oculomotor deficits in a psychometric schizotypy sample and (2) to investigate whether the expected deficits can be remedied by compounds shown to ameliorate impairments in schizophrenia. METHODS: In this randomized double-blind, placebo-controlled study 233 healthy participants performed prosaccade (PS), antisaccade (AS) and smooth pursuit eye movement (SPEM) tasks after being randomly assigned to one of four drug groups (nicotine, risperidone, amisulpride, placebo). Participants were classified into medium- and high-schizotypy groups based on their scores on the Schizotypal Personality Questionnaire (SPQ, Raine (Schizophr Bull 17:555-564, 1991)). RESULTS: AS error rate showed a main effect of Drug (p < 0.01), with nicotine improving performance, and a Drug by Schizotypy interaction (p = 0.04), indicating higher error rates in medium schizotypes (p = 0.01) but not high schizotypes under risperidone compared to placebo. High schizotypes had higher error rates than medium schizotypes under placebo (p = 0.03). There was a main effect of Drug for saccadic peak velocity and SPEM velocity gain (both p </= 0.01) indicating impaired performance with risperidone. CONCLUSIONS: We replicate the observation of AS impairments in high schizotypy under placebo and show that nicotine enhances performance irrespective of group status. Caution should be exerted in applying this model as no beneficial effects of antipsychotics were seen in high schizotypes. |
Anne Schmechtig; Jane Lees; Adam M. Perkins; A. Altavilla; Kevin J. Craig; G. R. Dawson; J. F. William Deakin; Colin T. Dourish; L. H. Evans; Ivan Koychev; K. Weaver; R. Smallman; J. Walters; L. S. Wilkinson; R. Morris; Steve C. R. Williams; Ulrich Ettinger The effects of ketamine and risperidone on eye movement control in healthy volunteers Journal Article In: Translational Psychiatry, vol. 3, pp. e334, 2013. @article{Schmechtig2013, The non-competitive N-methyl-D-aspartate receptor antagonist ketamine leads to transient psychosis-like symptoms and impairments in oculomotor performance in healthy volunteers. This study examined whether the adverse effects of ketamine on oculomotor performance can be reversed by the atypical antipsychotic risperidone. In this randomized double-blind, placebo-controlled study, 72 healthy participants performed smooth pursuit eye movements (SPEM), prosaccades (PS) and antisaccades (AS) while being randomly assigned to one of four drug groups (intravenous 100 ng ml(-1) ketamine, 2 mg oral risperidone, 100 ng ml(-1) ketamine plus 2 mg oral risperidone, placebo). Drug administration did not lead to harmful adverse events. Ketamine increased saccadic frequency and decreased velocity gain of SPEM (all P < 0.01) but had no significant effects on PS or AS (all P > or = 0.07). An effect of risperidone was observed for amplitude gain and peak velocity of PS and AS, indicating hypometric gain and slower velocities compared with placebo (both P < or = 0.04). No ketamine by risperidone interactions were found (all P > or = 0.26). The results confirm that the administration of ketamine produces oculomotor performance deficits similar in part to those seen in schizophrenia. The atypical antipsychotic risperidone did not reverse ketamine-induced deteriorations. These findings do not support the cognitive enhancing potential of risperidone on oculomotor biomarkers in this model system of schizophrenia and point towards the importance of developing alternative performance-enhancing compounds to optimise pharmacological treatment of schizophrenia. |
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. |
Maria Solé Puig; Laura Pérez Zapata; J. Antonio Aznar-Casanova; Hans Supèr; Maria Solé Puig; Laura Perez Zapata; Hans Super A role of eye vergence in covert attention Journal Article In: PLoS ONE, vol. 8, no. 1, pp. e52955, 2013. @article{SolePuig2013, Covert spatial attention produces biases in perceptual and neural responses in the absence of overt orienting movements. The neural mechanism that gives rise to these effects is poorly understood. Here we report the relation between fixational eye movements, namely eye vergence, and covert attention. Visual stimuli modulate the angle of eye vergence as a function of their ability to capture attention. This illustrates the relation between eye vergence and bottom-up attention. In visual and auditory cue/no-cue paradigms, the angle of vergence is greater in the cue condition than in the no-cue condition. This shows a top-down attention component. In conclusion, observations reveal a close link between covert attention and modulation in eye vergence during eye fixation. Our study suggests a basis for the use of eye vergence as a tool for measuring attention and may provide new insights into attention and perceptual disorders. |
Irene Sperandio; Shaleeza Kaderali; Philippe A. Chouinard; Jared Frey; Melvyn A. Goodale Perceived size change induced by nonvisual signals in darkness: The relative contribution of vergence and proprioception Journal Article In: Journal of Neuroscience, vol. 33, no. 43, pp. 16915–16923, 2013. @article{Sperandio2013, Most of the time, the human visual system computes perceived size by scaling the size of an object on the retina with its perceived distance. There are instances, however, in which size-distance scaling is not based on visual inputs but on extraretinal cues. In the Taylor illusion, the perceived afterimage that is projected on an observer's hand will change in size depending on how far the limb is positioned from the eyes-even in complete darkness. In the dark, distance cues might derive from hand position signals either by an efference copy of the motor command to the moving hand or by proprioceptive input. Alternatively, there have been reports that vergence signals from the eyes might also be important. We performed a series of behavioral and eye-tracking experiments to tease apart how these different sources of distance information contribute to the Taylor illusion. We demonstrate that, with no visual information, perceived size changes mainly as a function of the vergence angle of the eyes, underscoring its importance in size-distance scaling. Interestingly, the strength of this relationship decreased when a mismatch between vergence and proprioception was introduced, indicating that proprioceptive feedback from the arm also affected size perception. By using afterimages, we provide strong evidence that the human visual system can benefit from sensory signals that originate from the hand when visual information about distance is unavailable. |
Miriam Spering; Elisa C. Dias; Jamie L. Sanchez; Alexander C. Schutz; Daniel C. Javitt Efference copy failure during smooth pursuit eye movements in schizophrenia Journal Article In: Journal of Neuroscience, vol. 33, no. 29, pp. 11779–11787, 2013. @article{Spering2013, Abnormal smooth pursuit eye movements in patients with schizophrenia are often considered a consequence of impaired motion perception. Here we used a novel motion prediction task to assess the effects of abnormal pursuit on perception in human patients. Schizophrenia patients (n = 15) and healthy controls (n = 16) judged whether a briefly presented moving target ("ball") would hit/miss a stationary vertical line segment ("goal"). To relate prediction performance and pursuit directly, we manipulated eye movements: in half of the trials, observers smoothly tracked the ball; in the other half, they fixated on the goal. Strict quality criteria ensured that pursuit was initiated and that fixation was maintained. Controls were significantly better in trajectory prediction during pursuit than during fixation, their performance increased with presentation duration, and their pursuit gain and perceptual judgments were correlated. Such perceptual benefits during pursuit may be due to the use of extraretinal motion information estimated from an efference copy signal. With an overall lower performance in pursuit and perception, patients showed no such pursuit advantage and no correlation between pursuit gain and perception. Although patients' pursuit showed normal improvement with longer duration, their prediction performance failed to benefit from duration increases. This dissociation indicates relatively intact early visual motion processing, but a failure to use efference copy information. Impaired efference function in the sensory system may represent a general deficit in schizophrenia and thus contribute to symptoms and functional outcome impairments associated with the disorder. |
Andreas Sprenger; Peter Trillenberg; Matthias Nagel; John A. Sweeney; Rebekka Lencer Enhanced top-down control during pursuit eye tracking in schizophrenia Journal Article In: European Archives of Psychiatry and Clinical Neuroscience, vol. 263, no. 3, pp. 223–231, 2013. @article{Sprenger2013a, Alterations in sensorimotor processing and predictive mechanisms have both been proposed as the primary cause of eye tracking deficits in schizophrenia. 20 schizophrenia patients and 20 healthy controls were assessed on blocks of predictably moving visual targets at constant speeds of 10, 15 or 30 degrees /s. To assess internal drive to the eye movement system based on predictions about the ongoing target movement, targets were blanked off for either 666 or 1,000 ms during the ongoing pursuit movement in additional conditions. Main parameters of interest were eye deceleration after extinction of the visual target and residual eye velocity during blanking intervals. Eye deceleration after target extinction, reflecting persistence of predictive signals, was slower in patients than in controls, implying greater rather than diminished utilization of predictive mechanisms for pursuit in schizophrenia. Further, residual gain was not impaired in patients indicating a basic integrity of internal predictive models. Pursuit velocity gain in patients was reduced in all conditions with visible targets replicating previous findings about a sensorimotor transformation deficit in schizophrenia. A pattern of slower eye deceleration and unimpaired residual gain during blanking intervals implies greater adherence to top-down predictive models for pursuit tracking in schizophrenia. This suggests that predictive modeling is relatively intact in schizophrenia and that the primary cause of abnormal visual pursuit is impaired sensorimotor transformation of the retinal error signal needed for the maintenance of accurate visually driven pursuit. This implies that disruption in extrastriate and sensorimotor systems rather than frontostriatal predictive mechanisms may underlie this widely reported endophenotypes for schizophrenia. |
2012 |
Alexander C. Schutz There's more behind it: Perceived depth order biases perceived numerosity/density Journal Article In: Journal of Vision, vol. 12, no. 12, pp. 1–16, 2012. @article{Schutz2012, Humans have a clear sense of the numerosity of elements in a surface. However, recent studies showed that the binding of features to the single elements is severely limited. By studying the relationship of depth order and perceived numerosity of overlapping, pseudotransparent surfaces, we show that the binding of elements to the surfaces is also limited. In transparent motion, anisotropies for perceived depth order and perceived numerosity were highly correlated: directions that were more likely to be perceived in the back were also more likely to be perceived as more numerous. The magnitude of anisotropies, however, was larger for depth order than for numerosity, and the correlation with eye movement anisotropies also developed earlier for depth order than for numerosity judgments. Presenting the surfaces at different disparities removed the anisotropies but lead to a consistent bias to overestimate the numerosity of the surface in the back and to underestimate the surface in the front. The magnitude of this bias did not depend on dot density or lifetime. However when the speed of motion was reduced or when the two surfaces were presented at different luminance polarities, the magnitude of anisotropies and the numerosity bias were greatly reduced. These results show that the numerosity of pseudotransparent surfaces is not processed independent of the depth structure in the scene. Instead there is a strong prior for higher numerosity in the back surface. |
Alexander C. Schutz; Julia Trommershäuser; Karl R. Gegenfurtner Dynamic integration of information about salience and value for saccadic eye movements Journal Article In: Proceedings of the National Academy of Sciences, vol. 109, no. 19, pp. 7547–7552, 2012. @article{Schutz2012a, Humans shift their gaze to a new location several times per second. It is still unclear what determines where they look next. Fixation behavior is influenced by the low-level salience of the visual stimulus, such as luminance, contrast, and color, but also by high-level task demands and prior knowledge. Under natural conditions, different sources of information might conflict with each other and have to be combined. In our paradigm, we trade off visual salience against expected value. We show that both salience and value information influence the saccadic end point within an object, but with different time courses. The relative weights of salience and value are not constant but vary from eye movement to eye movement, depending critically on the availability of the value information at the time when the saccade is programmed. Short-latency saccades are determined mainly by salience, but value information is taken into account for long-latency saccades. We present a model that describes these data by dynamically weighting and integrating detailed topographic maps of visual salience and value. These results support the notion of independent neural pathways for the processing of visual information and value. |
Xue-feng F. Shi; Li-min Xu; Yao Li; Ting Wang; Kan-xing Zhao; Bernhard A. Sabel Fixational saccadic eye movements are altered in anisometropic amblyopia Journal Article In: Restorative Neurology and Neuroscience, vol. 30, no. 6, pp. 445–462, 2012. @article{Shi2012a, PURPOSE: Amblyopia develops during a critical period in early visual development and is characterized by reduced visual sensory functions and structural reorganization of the brain. However, little is known about oculomotor functions in amblyopes despite the special role of eye movements in visual perception, task execution and fixation. Therefore, we studied the relationship of visual deficits in anisometropic amblyopia and fixational saccadic eye movements. METHODS: We recruited twenty-eight anisometropic amblyopes and twenty-eight age-matched control subjects. Using a high-speed eye-tracker, fixational eye-movements of both eyes were recorded. A computerized fixational saccadic component analysis of eye-movement waveforms was developed to quantify the parameters of fixational saccades (FSs) and a simulation model was developed to help explain the FS performances. RESULTS: Amblyopic eyes, but not control eyes, showed fewer FSs, but these had increased amplitudes, increased peak velocities, and longer inter-saccadic intervals. The reduced FSs occurred mainly in the 0- to 0.6-degree amplitude range, and the probability of FSs with larger amplitudes and longer inter-saccadic intervals was significantly higher than in controls. A new simulation model analysis suggests that an excitatory-inhibitory activity imbalance in superior colliculus may explain these FSs changes. CONCLUSIONS: We propose that the abnormal visual processing and circuitry reorganization in anisometropic amblyopia has an impact on the fixational saccade generation. We see two possible interpretations: (i) altered FSs may be an attempt of the visual system to adapt to the deficit, trying to capture more information from a broader spatial domain of the visual world so as to enhance the contrast sensitivity to low spatial frequencies viewed by the amblyopic eye, or (ii) it may be the cause of amblyopia or a contributing factor to the original deficit that aggravates the early deprivation. |
David Souto; Dirk Kerzel Like a rolling stone: Naturalistic kinematics influence tracking eye movements Journal Article In: Journal of Vision, vol. 12, no. 9, pp. 1–12, 2012. @article{Souto2012, Newtonian physics constrains object kinematics in the real world. We asked whether eye movements towards tracked objects depend on their compliance with those constraints. In particular, the force of gravity constrains round objects to roll on the ground with a particular rotational and translational motion. We measured tracking eye movements towards rolling objects. We found that objects with rotational and translational motion that was congruent with an object rolling on the ground elicited faster tracking eye movements during pursuit initiation than incongruent stimuli. Relative to a condition without rotational component, we compared objects with this motion with a condition in which there was no rotational component, we essentially obtained benefits of congruence, and, to a lesser extent, costs from incongruence. Anticipatory pursuit responses showed no congruence effect, suggesting that the effect is based on visually-driven predictions, not on velocity storage. We suggest that the eye movement system incorporates information aSouto, D., & Kerzel, D. (2012). Like a rolling stone: naturalistic kinematics influence tracking eye movements. Journal of Vision, 12(9), 997–997. https://doi.org/10.1167/12.9.997bout object kinematics acquired by a lifetime of experience with visual stimuli obeying the laws of Newtonian physics. |
Martin Szinte; Mark Wexler; Patrick Cavanagh Temporal dynamics of remapping captured by peri-saccadic continuous motion Journal Article In: Journal of Vision, vol. 12, no. 7, pp. 1–18, 2012. @article{Szinte2012, Different attention and saccade control areas contribute to space constancy by remapping target activity onto their expected post-saccadic locations. To visualize this dynamic remapping, we used a technique developed by Honda (2006) where a probe moved vertically while participants made a saccade across the motion path. Observers do not report any large excursions of the trace at the time of the saccade that would correspond to the classical peri-saccadic mislocalization effect. Instead, they reported that the motion trace appeared to be broken into two separate segments with a shift of approximately one-fifth of the saccade amplitude representing an overcompensation of the expected retinal displacement caused by the saccade. To measure the timing of this break in the trace, we introduced a second, physical shift that was the same size but opposite in direction to the saccade-induced shift. The trace appeared continuous most frequently when the physical shift was introduced at the midpoint of the saccade, suggesting that the compensation is in place when the saccade lands. Moreover, this simple linear shift made the combined traces appear continuous and linear, with no curvature. In contrast, Honda (2006) had reported that the pre- and post-saccadic portion of the trace appeared aligned and that there was often a small, visible excursion of the trace at the time of the saccade. To compare our results more directly, we increased the contrast of our moving probe in a third experiment. Now some observers reported seeing a deviation in the motion path but the misalignment remained present. We conclude that the large deviations at the time of saccade are generally masked for a continuously moving target but that there is nevertheless a residual misalignment between pre- and post-saccadic coordinates of approximately 20% of the saccade amplitude that normally goes unnoticed. |
A. Caglar Tas; Cathleen M. Moore; Andrew Hollingworth An object-mediated updating account of insensitivity to transsaccadic change Journal Article In: Journal of Vision, vol. 12, no. 11, pp. 1–13, 2012. @article{Tas2012a, Recent evidence has suggested that relatively precise information about the location and visual form of a saccade target object is retained across a saccade. However, this information appears to be available for report only when the target is removed briefly, so that the display is blank when the eyes land. We hypothesized that the availability of precise target information is dependent on whether a post-saccade object is mapped to the same object representation established for the presaccade target. If so, then the post-saccade features of the target overwrite the presaccade features, a process of object mediated updating in which visual masking is governed by object continuity. In two experiments, participants' sensitivity to the spatial displacement of a saccade target was improved when that object changed surface feature properties across the saccade, consistent with the prediction of the object-mediating updating account. Transsaccadic perception appears to depend on a mechanism of object-based masking that is observed across multiple domains of vision. In addition, the results demonstrate that surface-feature continuity contributes to visual stability across saccades. |
Jianliang Tong; Zhi-Lei Zhang; Christopher R. L. Cantor; Clifton M. Schor The effect of perceptual grouping on perisaccadic spatial distortions Journal Article In: Journal of Vision, vol. 12, no. 10, pp. 1–16, 2012. @article{Tong2012, Perisaccadic spatial distortion (PSD) occurs when a target is flashed immediately before the onset of a saccade and it appears displaced in the direction of the saccade. In previous studies, the magnitude of PSD of a single target was affected by multiple experimental parameters, such as the target's luminance and its position relative to the central fixation target. Here we describe a contextual effect in which the magnitude of the PSD for a target was influenced by the synchronous presentation of another target: PSD for simultaneously presented targets was more uniform than when each was presented individually. Perisaccadic compression was ruled out as a causal factor, and the results suggest that both low- and high-level perceptual grouping mechanisms may account for the change in PSD magnitude. We speculate that perceptual grouping could play a key role in preserving shape constancy during saccadic eye movements. |
Stefan Van der Stigchel; Jessica Heeman; Tanja C. W. Nijboer Averaging is not everything: The saccade global effect weakens with increasing stimulus size Journal Article In: Vision Research, vol. 62, pp. 108–115, 2012. @article{VanderStigchel2012a, When two elements are presented closely aligned, the average saccade endpoint will generally be located in between these two elements. This 'global effect' has been explained in terms of the center of gravity account which states that the saccade endpoint is based on the relative saliency of the different elements in the visual display. In the current study, we tested one of the implications of the center of gravity account: when two elements are presented closely aligned with the same size and the same distance from central fixation, the saccade should land on the intermediate location, irrespective of the stimulus size. To this end, two equally-sized elements were presented simultaneously and participants were required to execute an eye movement to the visual information presented on the display. Results showed that the strongest global effect was observed in the condition with smaller stimuli, whereas the saccade averaging was weaker when larger stimuli were presented. In a second experiment, in which only one element was presented, we observed that the width of the distribution of saccade endpoints is influenced by stimulus size in that the distribution is broader with smaller stimuli. We conclude that perfect saccade averaging is not always the default response by the oculomotor system. There appears to be a tendency to initiate an eye movement towards one of the visual elements, which becomes stronger with increasing stimulus size. This effect might be explained by an increased uncertainty in target localization for smaller stimuli, resulting in a higher probability of the merging of two stimulus representations into one representation. |
Nathan Van der Stoep; Tanja C. W. Nijboer; Stefan Van der Stigchel Non-lateralized auditory input enhances averaged vectors in the oculomotor system Journal Article In: Experimental Brain Research, vol. 221, no. 4, pp. 377–384, 2012. @article{VanderStoep2012, The decision about which location should be the goal of the next eye movement is known to be determined by the interaction between auditory and visual input. This interaction can be explained by the vector theory that states that each element (either visual or auditory) in a scene evokes a vector in the oculomotor system. These vectors determine the direction in which the eye movement is initiated. Because auditory input is lateralized and localizable in most studies, it is currently unclear how non-lateralized auditory input interacts with the vectors evoked by visual input. In the current study, we investigated the influence of a non-lateralized auditory non-target on saccade accuracy (saccade angle deviation from the target) and latency in a single-target condition in Experiment 1 and a double-target condition in Experiment 2. The visual targets in Experiment 2 were positioned in such a way that saccades on average landed in between the two targets (i.e., a global effect). There was no effect of the auditory input on saccade accuracy in the single-target condition, but auditory input did influence saccade accuracy in the double-target condition. In both experiments, saccade latency increased when auditory input accompanied the visual target(s). Together, these findings show that non-lateralized auditory input enhances all vectors evoked by visual input. The results will be discussed in terms of their possible neural substrates. |
Polina M. Vanyukov; Tessa Warren; Mark E. Wheeler; Erik D. Reichle The emergence of frequency effects in eye movements Journal Article In: Cognition, vol. 123, no. 1, pp. 185–189, 2012. @article{Vanyukov2012, A visual search experiment employed strings of Landolt Cs to examine how the gap size of and frequency of exposure to distractor strings affected eye movements. Increases in gap size were associated with shorter first-fixation durations, gaze durations, and total times, as well as fewer fixations. Importantly, both the number and duration of fixations decreased with repeated exposures. The findings provide evidence for the role of cognition in guiding eye-movements, and a potential explanation for word-frequency effects observed in reading. |
Dorine Vergilino-Perez; Alexandra Fayel; Christelle Lemoine; Patrice Senot; Judith Vergne; Karine Doré-Mazars Are there any left-right asymmetries in saccade parameters? Examination of latency, gain, and peak velocity Journal Article In: Investigative Ophthalmology & Visual Science, vol. 53, no. 7, pp. 3340–3348, 2012. @article{VergilinoPerez2012, PURPOSE Hemispheric specialization in saccadic control is still under debate. Here we examine the latency, gain, and peak velocity of reactive and voluntary leftward and rightward saccades to assess the respective roles of eye and hand dominance. METHODS Participants with contrasting hand and eye dominance were asked to make saccades toward a target displayed at 5°, 10°, or 15° left or right of the central fixation point. In separate sessions, reactive and voluntary saccades were elicited by Gap-200, Gap-0, Overlap-600, and Antisaccade procedures. RESULTS Left-right asymmetries were not found in saccade latencies but appeared in saccade gain and peak velocity. Regardless of the dominant hand, saccades directed to the ipsilateral side relative to the dominant eye had larger amplitudes and faster peak velocities. CONCLUSIONS Left-right asymmetries can be explained by naso-temporal differences for some subjects and by eye dominance for others. Further investigations are needed to examine saccadic parameters more systematically in relation to eye dominance. Indeed, any method that allows one to determine ocular dominance from objective measures based on saccade parameters should greatly benefit clinical applications, such as monovision surgery. |
Petra Vetter; Grace Edwards; Lars Muckli Transfer of predictive signals across saccades Journal Article In: Frontiers in Psychology, vol. 3, pp. 176, 2012. @article{Vetter2012, Predicting visual information facilitates efficient processing of visual signals. Higher visual areas can support the processing of incoming visual information by generating predictive models that are fed back to lower visual areas. Functional brain imaging has previously shown that predictions interact with visual input already at the level of the primary visual cortex (V1; Harrison et al., 2007; Alink et al., 2010). Given that fixation changes up to four times a second in natural viewing conditions, cortical predictions are effective in V1 only if they are fed back in time for the processing of the next stimulus and at the corresponding new retinotopic position. Here, we tested whether spatio-temporal predictions are updated before, during, or shortly after an inter-hemifield saccade is executed, and thus, whether the predictive signal is transferred swiftly across hemifields. Using an apparent motion illusion, we induced an internal motion model that is known to produce a spatio-temporal prediction signal along the apparent motion trace in V1 (Muckli et al., 2005; Alink et al., 2010). We presented participants with both visually predictable and unpredictable targets on the apparent motion trace. During the task, participants saccaded across the illusion whilst detecting the target. As found previously, predictable stimuli were detected more frequently than unpredictable stimuli. Furthermore, we found that the detection advantage of predictable targets is detectable as early as 50-100 ms after saccade offset. This result demonstrates the rapid nature of the transfer of a spatio-temporally precise predictive signal across hemifields, in a paradigm previously shown to modulate V1. |
Jing Wang; Ruobing Xia; Mingsha Zhang; Yujun Pan Long term retention of saccadic adaptation is induced by a dark environmental context Journal Article In: Brain Research, vol. 1489, pp. 56–65, 2012. @article{Wang2012e, Under many circumstances, motor memory needs to be retained for a long period of time to enable accurate behavior. Since the first introduction of the saccadic adaptation paradigm in 1960s, saccadic adaptation protocols have been widely used to study the mechanisms of motor learning and motor memory. However, previous studies reported that the effect of saccadic adaptation on the oculomotor system was rather short (minutes to hours) in human and non-human primates. Here we ask whether the fast decay of the effects of saccadic adaptation is due to the influence of environmental context. To test this hypothesis, we asked human subjects to perform a saccadic adaptation task in a very dark environment. Our data showed that saccade gain remained at the post-adaptation level 24-72 h after exposure to the saccadic adaptation task without significant recovery, and that the effect of saccadic adaptation on saccade gain could still be found 2 months later, much longer than previously reported. Our results indicate a vital role for environmental context in the retention of saccadic adaptation. |
Dagmar A. Wismeijer; Karl R. Gegenfurtner Orientation of noisy texture affects saccade direction during free viewing Journal Article In: Vision Research, vol. 58, pp. 19–26, 2012. @article{Wismeijer2012, We redirect our eye approximately three times per second to bring a new part of our environment on to our fovea (Findlay & Gilchrist, 2003). How a scanning path is planned is still an unsolved matter. Most research to date has focused on the question of target selection: how is the next fixation location, or saccade target, selected. Here we investigated the direction of spontaneous saccades, rather than fixation locations per se. We measured eye movements, while observers were freely viewing noisy textures: oriented gabors embedded in either pink (1/f) noise or pixel noise, of which they later had to report their orientation. Our results show that a significant percentage of the spontaneous saccades were directed along the orientation of the stimulus. These results suggest that observers may have used an underlying eye movement strategy involving the search for contour endings. |
Takemasa Yokoyama; Yasuki Noguchi; Shinichi Kita Attentional shifts by gaze direction in voluntary orienting: evidence from a microsaccade study Journal Article In: Experimental Brain Research, vol. 223, no. 2, pp. 291–300, 2012. @article{Yokoyama2012, Shifts in spatial attention can be induced by the gaze direction of another. However, it is unclear whether gaze direction influences the allocation of attention by reflexive or voluntary orienting. The present study was designed to examine which type of attentional orienting is elicited by gaze direction. We conducted two experiments to answer this question. In Experiment 1, we used a modified Posner paradigm with gaze cues and measured microsaccades to index the allocation of attention. We found that microsaccade direction followed cue direction between 200 and 400 ms after gaze cues were presented. This is consistent with the latencies observed in other microsaccade studies in which voluntary orienting is manipulated, suggesting that gaze direction elicits voluntary orienting. However, Experiment 1 did not separate voluntary and reflexive orienting directionally, so in Experiment 2, we used an anticue task in which cue direction (direction to allocate attention) was the opposite of gaze direction (direction of gaze in depicted face). The results in Experiment 2 were consistent with those from Experiment 1. Microsaccade direction followed the cue direction, not gaze direction. Taken together, these results indicate that the shift in spatial attention elicited by gaze direction is voluntary orienting. |
Hao Zhang; Hong-Mei Yan; Keith M. Kendrick; Chao-Yi Li Both lexical and non-lexical characters are processed during saccadic eye movements Journal Article In: PLoS ONE, vol. 7, no. 9, pp. e46383, 2012. @article{Zhang2012, On average our eyes make 3-5 saccadic movements per second when we read, although their neural mechanism is still unclear. It is generally thought that saccades help redirect the retinal fovea to specific characters and words but that actual discrimination of information only occurs during periods of fixation. Indeed, it has been proposed that there is active and selective suppression of information processing during saccades to avoid experience of blurring due to the high-speed movement. Here, using a paradigm where a string of either lexical (Chinese) or non-lexical (alphabetic) characters are triggered by saccadic eye movements, we show that subjects can discriminate both while making saccadic eye movement. Moreover, discrimination accuracy is significantly better for characters scanned during the saccadic movement to a fixation point than those not scanned beyond it. Our results showed that character information can be processed during the saccade, therefore saccades during reading not only function to redirect the fovea to fixate the next character or word but allow pre-processing of information from the ones adjacent to the fixation locations to help target the next most salient one. In this way saccades can not only promote continuity in reading words but also actively facilitate reading comprehension. |
Albert Moukheiber; Gilles Rautureau; Fernando Perez-Diaz; Roland Jouvent; Antoine Pelissolo Gaze behaviour in social blushers Journal Article In: Psychiatry Research, vol. 200, no. 2-3, pp. 614–619, 2012. @article{Moukheiber2012, Gaze aversion could be a central component of social phobia. Fear of blushing is a symptom of social anxiety disorder (SAD) but is not yet described as a specific diagnosis in psychiatric classifications. Our research consists of comparing gaze aversion in SAD participants with or without fear of blushing in front of pictures of different emotional faces using an eye tracker. Twenty-six participants with DSM-IV SAD and expressed fear of blushing (SAD+FB) were recruited in addition to twenty-five participants with social phobia and no fear of blushing (SAD-FB). Twenty-four healthy participants aged and sex matched constituted the control group. We studied the number of fixations and the dwell time in the eyes area on the pictures. The results showed gaze avoidance in the SAD-FB group when compared to controls and when compared to the SAD+FB group. However we found no significant difference between SAD+FB and controls. We also observed a correlation between the severity of the phobia and the degree of gaze avoidance across groups. These findings seem to support the claim that social phobia is a heterogeneous disorder. Further research is advised to decide whether fear of blushing can constitute a subtype with specific behavioral characteristics. |
Amy Nau; Richard W. Hertle; Dongsheng Yang Effect of tongue stimulation on nystagmus eye movements in blind patients Journal Article In: Brain Structure and Function, vol. 217, no. 3, pp. 761–765, 2012. @article{Nau2012, We have observed dramatic effects of tactile tongue stimulation on nystagmus eye movements in patients with acquired blindness, and we report these results. Six adult subjects (3 subjects with light perception or worse vision and 3 normal subjects) were included in this study. Causes of blindness included traumatic explosion, anterior ischemic optic neuropathy, and central retinal artery occlusion. Duration of blindness was 15, 3 and 1.5 years, respectively. A video eye tracking system (Eyelink 1000) was used to record eye movements. The eye movement recording (EMR) was repeated four times in a span of 20 min. Two of the EMRs were performed without tongue stimulation and two with tongue stimulation in randomized order. A tongue stimulus was applied to the surface of the tongue using a Brainport device that produces an electrical tactile stimulus. The nystagmus waveform characteristics and frequency were analyzed. We found that all blind subjects showed continuous jerk nystagmus with slow and quick phases, mainly in horizontal plane in their primary eye positions. The recorded nystagmus waveforms were jerk with linear velocity slow phases. When the tongue stimulus was applied, the frequency of nystagmus was significantly reduced by 47, 40, and 11%, and relative amplitude was reduced by 43, 45, and 6% for three blind subjects, respectively. In conclusion, we think our results that tongue stimulation influences nystagmus eye movements support a link between non-visual sensory input and ocular motor activity. |
Isabel Dombrowe; Mieke Donk; Hayley Wright; Christian N. L. Olivers; Glyn W. Humphreys The contribution of stimulus-driven and goal-driven mechanisms to feature-based selection in patients with spatial attention deficits Journal Article In: Cognitive Neuropsychology, vol. 29, no. 3, pp. 249–274, 2012. @article{Dombrowe2012, When people search a display for a target defined by a unique feature, fast saccades are predominantly stimulus-driven whereas slower saccades are primarily goal-driven. Here we use this dissociative pattern to assess whether feature-based selection in patients with lateralized spatial attention deficits is impaired in stimulus-driven processing, goal-driven processing, or both. A group of patients suffering from extinction or neglect after parietal damage, and a group of healthy, age-matched controls, were instructed to make a saccade to a uniquely oriented target line which was presented simultaneously with a differently oriented distractor line. We systematically varied the salience of the target and distractor by changing the orientation of background elements, and used a time-based model to extract stimulus-driven (salience) and goal-driven (target set) components of selection. The results show that the patients exhibited reduced stimulus-driven processing only in the contralesional hemifield, while goal-driven processing was reduced across both hemifields. |
Matthieu Philippe; Anne-Emmanuelle Priot; Phillippe Fuchs; Corinne Roumes Vergence tracking: A tool to assess oculomotor performance in stereoscopic displays Journal Article In: Journal of Eye Movement Research, vol. 5, no. 2, pp. 1–8, 2012. @article{Philippe2012, Oculomotor conflict induced between the accommodative and vergence components in stereoscopic displays represents an unnatural viewing condition. There is now some evidence that stereoscopic viewing may induce discomfort and changes in oculomotor parameters. The present study sought to measure oculomotor performance during stereoscopic viewing. Using a 3D stereo setup and an eye-tracker, vergence responses were measured during 20-min exposure to a virtual visual target oscillating in depth, which participants had to track. The results showed a significant decline in the amplitude of the in-depth oscillatory vergence response over time. We propose that eye-tracking provides a useful tool to objectively assess the timevarying alterations of the vergence system when using stereoscopic displays. |
Tara Rastgardani; Mathias Abegg; Jason J. S. Barton The inter-trial spatial biases of stimuli and goals in saccadic programming Journal Article In: Journal of Eye Movement Research, vol. 7, no. 4, pp. 1–7, 2012. @article{Rastgardani2012, Prior studies have shown an ‘alternate antisaccade-goal bias', in that the saccadic landing points of antisaccades were displaced towards the location of antisaccade goals used in other trials in the same experimental block. Thus the motor response in one trial induced a spatial bias of a motor response in another trial. In this study we investigated whether sensory information, i.e. the location of a visual stimulus, might have a spatial effect on a motor response too. Such an effect might be attractive as for the alternate antisaccade-goal bias or repulsive. For this purpose we used block of trials with either antisaccades, prosaccades or mixed trials in order to study the alternate-trial biases generated by antisaccade goals, antisaccade stimuli, and prosaccade goals. in contrast to the effects of alternate antisaccade goals described in prior studies, alternate antisaccade stimuli generated a significant repulsive bias of about 1.8°: furthermore, if stimulus and motor goal coincide, as with an alternate prosaccade, the repulsive effect of a stimulus prevails, causing a bias of about 0.9°. Taken together with prior results, these findings may reflect averaging of current and alternate trial activity in a salience map, with excitatory activity from the motor response and inhibitory activity from the sensory input. |
Kay L. Ritchie; Amelia R. Hunt; Arash Sahraie Trans-saccadic priming in hemianopia: Sighted-field sensitivity is boosted by a blind-field prime Journal Article In: Neuropsychologia, vol. 50, no. 5, pp. 997–1005, 2012. @article{Ritchie2012, We experience visual stability despite shifts of the visual array across the retina produced by eye movements. A process known as remapping is thought to keep track of the spatial locations of objects as they move on the retina. We explored remapping in damaged visual cortex by presenting a stimulus in the blind field of two patients with hemianopia. When they executed a saccadic eye movement that would bring the stimulated location into the sighted field, reported awareness of the stimulus increased, even though the stimulus was removed before the saccade began and so never actually fell in the sighted field. Moreover, when a location was primed by a blind-field stimulus and then brought into the sighted field by a saccade, detection sensitivity for near-threshold targets appearing at this location increased dramatically. The results demonstrate that brain areas supporting conscious vision are not necessary for remapping, and suggest visual stability is maintained for salient objects even when they are not consciously perceived. |
Martin Rolfs; Marisa Carrasco Rapid simultaneous enhancement of visual sensitivity and perceived contrast during saccade preparation Journal Article In: Journal of Neuroscience, vol. 32, no. 40, pp. 13744–13752, 2012. @article{Rolfs2012, Humans and other animals with foveate vision make saccadic eye movements to prioritize the visual analysis of behaviorally relevant information. Even before movement onset, visual processing is selectively enhanced at the target of a saccade, presumably gated by brain areas controlling eye movements. Here we assess concurrent changes in visual performance and perceived contrast before saccades, and show that saccade preparation enhances perception rapidly, altering early visual processing in a manner akin to increasing the physical contrast of the visual input. Observers compared orientation and contrast of a test stimulus, appearing briefly before a saccade, to a standard stimulus, presented previously during a fixation period. We found simultaneous progressive enhancement in both orientation discrimination performance and perceived contrast as time approached saccade onset. These effects were robust as early as 60 ms after the eye movement was cued, much faster than the voluntary deployment of covert attention (without eye movements), which takes ∼300 ms. Our results link the dynamics of saccade preparation, visual performance, and subjective experience and show that upcoming eye movements alter visual processing by increasing the signal strength. |
Fabian Schnier; Markus Lappe Mislocalization of stationary and flashed bars after saccadic inward and outward adaptation of reactive saccades Journal Article In: Journal of Neurophysiology, vol. 107, no. 11, pp. 3062–3070, 2012. @article{Schnier2012, Recent studies have shown that saccadic inward adaptation (i.e., the shortening of saccade amplitude) and saccadic outward adaptation (i.e., the lengthening of saccade amplitude) rely on partially different neuronal mechanisms. There is increasing evidence that these differences are based on differences at the target registration or planning stages since outward but not inward adaptation transfers to hand-pointing and perceptual localization of flashed targets. Furthermore, the transfer of reactive saccade adaptation to long-duration overlap and scanning saccades is stronger after saccadic outward adaptation than that after saccadic inward adaptation, suggesting that modulated target registration stages during outward adaptation are increasingly used in the execution of saccades when the saccade target is visually available for a longer time. The difference in target presentation duration between reactive and scanning saccades is also linked to a difference in perceptual localization of different targets. Flashed targets are mislocalized after inward adaptation of reactive and scanning saccades but targets that are presented for a longer time (stationary targets) are mislocalized stronger after scanning than after reactive saccades. This link between perceptual localization and adaptation specificity suggests that mislocalization of stationary bars should be higher after outward than that after inward adaptation of reactive saccades. In the present study we test this prediction. We show that the relative amount of mislocalization of stationary versus flashed bars is higher after outward than that after inward adaptation of reactive saccades. Furthermore, during fixation stationary and flashed bars were mislocalized after outward but not after inward adaptation. Thus, our results give further evidence for different adaptation mechanisms between inward and outward adaptation and harmonize some recent research. |
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. |
Philip J. Benson; Sara A. Beedie; Elizabeth Shephard; Ina Giegling; Dan Rujescu; David M. St. Clair Simple viewing tests can detect eye movement abnormalities that distinguish schizophrenia cases from controls with exceptional accuracy Journal Article In: Biological Psychiatry, vol. 72, no. 9, pp. 716–724, 2012. @article{Benson2012, Background: We have investigated which eye-movement tests alone and combined can best discriminate schizophrenia cases from control subjects and their predictive validity. Methods: A training set of 88 schizophrenia cases and 88 controls had a range of eye movements recorded; the predictive validity of the tests was then examined on eye-movement data from 34 9-month retest cases and controls, and from 36 novel schizophrenia cases and 52 control subjects. Eye movements were recorded during smooth pursuit, fixation stability, and free-viewing tasks. Group differences on performance measures were examined by univariate and multivariate analyses. Model fitting was used to compare regression, boosted tree, and probabilistic neural network approaches. Results: As a group, schizophrenia cases differed from control subjects on almost all eye-movement tests, including horizontal and Lissajous pursuit, visual scanpath, and fixation stability; fixation dispersal during free viewing was the best single discriminator. Effects were stable over time, and independent of sex, medication, or cigarette smoking. A boosted tree model achieved perfect separation of the 88 training cases from 88 control subjects; its predictive validity on retest assessments and novel cases and control subjects was 87.8%. However, when we examined the whole data set of 298 assessments, a cross-validated probabilistic neural network model was superior and could discriminate all cases from controls with near perfect accuracy at 98.3%. Conclusions: Simple viewing patterns can detect eye-movement abnormalities that can discriminate schizophrenia cases from control subjects with exceptional accuracy. © 2012 Society of Biological Psychiatry. |
Valerie Benson; Monica S. Castelhano; Sheena K. Au-Yeung; Keith Rayner Eye movements reveal no immediate "WOW" ("which one's weird") effect in autism spectrum disorder Journal Article In: Quarterly Journal of Experimental Psychology, vol. 65, no. 6, pp. 1139–1150, 2012. @article{Benson2012a, Autism spectrum disorder (ASD) and typically developed (TD) adult participants viewed pairs of scenes for a simple " spot the difference " (STD) and a complex " which one's weird " (WOW) task. There were no group differences in the STD task. In the WOW task, the ASD group took longer to respond manually and to begin fixating the target " weird " region. Additionally, as indexed by the first-fixation duration into the target region, the ASD group failed to " pick up " immediately on what was " weird " . The findings are discussed with reference to the complex information processing theory of ASD (Minshew & Goldstein, 1998). |
Valerie Benson; Magdalena Ietswaart; David Milner Eye movements and verbal report in a single case of visual neglect Journal Article In: PLoS ONE, vol. 7, no. 8, pp. e43743, 2012. @article{Benson2012b, In this single case study, visuospatial neglect patient P1 demonstrated a dissociation between an intact ability to make appropriate reflexive eye movements to targets in the neglected field with latencies of <400 ms, while failing to report targets presented at such durations in a separate verbal detection task. In contrast, there was a failure to evoke the usually robust Remote Distractor Effect in P1, even though distractors in the neglected field were presented at above threshold durations. Together those data indicate that the tight coupling that is normally shown between attention and eye movements appears to be disrupted for low-level orienting in P1. A comparable disruption was also found for high-level cognitive processing tasks, namely reading and scene scanning. The findings are discussed in relation to sampling, attention and awareness in neglect. |
Douwe P. Bergsma; Joris A. Elshout; G. J. Wildt; Albert V. Berg Transfer effects of training-induced visual field recovery in patients with chronic stroke Journal Article In: Topics in Stroke Rehabilitation, vol. 19, no. 3, pp. 212–225, 2012. @article{Bergsma2012, OBJECTIVE: Visual training of light detection in the transition zone between blind and healthy hemianopic visual fields leads to improvement of color and simple pattern recognition. Recently, we demonstrated that visual field enlargement (VFE) also occurs when an area just beyond the transition zone is stimulated. In the current study, we attempted to determine whether this peripheral training also causes improvement in color and shape perception and reading speed. Further, we evaluated which measure of VFE relates best to improvements in performance: the average border shift (ABS) in degrees or the estimated amount of cortical surface gain (ECSG) in millimeters, using the cortical magnification factor (CMF). METHOD: Twelve patients received 40 sessions of 1-hour restorative function training (RFT). Before and after training, we measured visual fields and reading speed. Additionally, color and shape perception in the trained visual field area was measured in 7 patients.$backslash$n$backslash$nRESULTS: VFE was found for 9 of 12 patients. Significant improvements were observed in reading speed for 8 of 12 patients and in color and shape perception for 3 of 7 patients. ECSG correlates significantly with performance; ABS does not. Our data indicate that the threshold ECSG, needed for significant changes in color and shape perception and reading speed, is about 6 mm. CONCLUSIONS: White stimulus training-induced VFE can lead to improved color and shape perception and to increased reading speed in and beyond the pretraining transition zone if ECSG is sufficiently large. The latter depends on the eccentricity of the VFE. |
Eileen E. Birch; Jingyun Wang; Joost Felius; David R. Stager; Richard W. Hertle Fixation control and eye alignment in children treated for dense congenital or developmental cataracts Journal Article In: Journal of AAPOS, vol. 16, no. 2, pp. 156–160, 2012. @article{Birch2012, Background: Many children treated for cataracts develop strabismus and nystagmus; however, little is known about the critical period for adverse ocular motor outcomes with respect to age of onset and duration. Methods: Children who had undergone extraction of dense cataracts by the age of 5 years were enrolled postoperatively. Ocular alignment was assessed regularly throughout follow-up. Fixation stability and associated ocular oscillations were determined from eye movement recordings at ≥5 years old. Multivariate logistic regression was used to evaluate whether laterality (unilateral vs bilateral), age at onset, and/or duration of visual deprivation were associated with adverse ocular motor outcomes and to determine multivariate odds ratios (ORs). Results: A total of 41 children were included. Of these, 27 (66%) developed strabismus; 29 (71%) developed nystagmus. Congenital onset was associated with significant risk for strabismus (OR, 5.3; 95% CI, 1.1-34.1); infantile onset was associated with significant risk for nystagmus (OR, 13.6; 95% CI, 1.6-302). Duration >6 weeks was associated with significant risk for both strabismus (OR, 9.1; 95% CI, 1.9-54.2) and nystagmus (OR, 46.2; 95% CI, 6.0-1005). Congenital onset was associated with significant risk for interocular asymmetry in severity of nystagmus (OR, 25.0; 95% CI, 2.6-649), as was unilateral cataract (OR, 58.9; 95% CI, 5.1-2318). Conclusions: Laterality (unilateral vs bilateral) and age at onset were significant nonmodifiable risk factors for adverse ocular motor outcomes. Duration of deprivation was a significant modifiable risk factor for adverse ocular motor outcomes. The current study demonstrated that reduced risk for nystagmus and strabismus was associated with deprivation ≤6 weeks. |
Aneta Brzezicka; Izabela Krejtz; Ulrich Hecker; Jochen Laubrock Eye movement evidence for defocused attention in dysphoria: A perceptual span analysis Journal Article In: International Journal of Psychophysiology, vol. 85, no. 1, pp. 129–133, 2012. @article{Brzezicka2012, The defocused attention hypothesis (von Hecker and Meiser, 2005) assumes that negative mood broadens attention, whereas the analytical rumination hypothesis (Andrews and Thompson, 2009) suggests a narrowing of the attentional focus with depression. We tested these conflicting hypotheses by directly measuring the perceptual span in groups of dysphoric and control subjects, using eye tracking. In the moving window paradigm, information outside of a variable-width gaze-contingent window was masked during reading of sentences. In measures of sentence reading time and mean fixation duration, dysphoric subjects were more pronouncedly affected than controls by a reduced window size. This difference supports the defocused attention hypothesis and seems hard to reconcile with a narrowing of attentional focus. |
Robyn Burton; David P. Crabb; Nicholas D. Smith; Fiona C. Glen; David F. Garway-Heath Glaucoma and reading: Exploring the effects of contrast lowering of text Journal Article In: Optometry and Vision Science, vol. 89, no. 9, pp. 1282–1287, 2012. @article{Burton2012, PURPOSE: Past research has not fully ascertained the extent to which people with glaucoma have difficulties with reading. This study measures change in reading speed when letter contrast is reduced, to test the hypothesis that patients with glaucoma are more sensitive to letter contrast than age-similar visually healthy people. METHODS: Fifty-three patients with glaucoma [mean age: 66 years (standard deviation: 9)] with bilateral visual field (VF) defects and 40 age-similar visually healthy control subjects [mean age: 69 (standard deviation: 8) years] had reading speeds measured using sets of fixed size, non-scrolling texts on a computer setup that incorporated an eye tracking device. All participants had visual acuity ≥6/9, and they underwent standard tests of visual function including Humphrey 24-2 and 10-2 VFs. Potential non-visual confounders were also tested, including cognitive ability (Middlesex Elderly Assessment of Mental Status Test) and general reading ability. Individual average raw reading speeds were calculated from 8 trials (different passages of text) at both 100% and 20% letter contrast. RESULTS: Patients had an average 24-2 VF MD of -6.5 (range: 0.7 to -17.3) dB in the better eye. The overall median reduction in reading speed due to decreasing the contrast of the text in the patients was 20%, but with considerable between-individual variation (interquartile range, 8%-44%). This reduction was significantly greater (p = 0.01) than the controls [median: 11% (interquartile range, 6%-17%)]. Patients and controls had similar average performance on Middlesex Elderly Assessment of Mental Status Test (p = 0.71), a modified Burt Reading ability test (p = 0.33), and a computer-based lexical decision task (p = 0.53) and had similar self-reported day-to-day reading frequency (p = 0.12). CONCLUSIONS: Average reduction in reading speed caused by a difference in letter contrast between 100% and 20% is significantly more apparent in patients with glaucoma when compared with visually healthy people with a similar age and similar cognitive/reading ability. |
Shaobo Guan; Yu Liu; Ruobing Xia; Mingsha Zhang Covert attention regulates saccadic reaction time by routing between different visual-oculomotor pathways Journal Article In: Journal of Neurophysiology, vol. 107, no. 6, pp. 1748–1755, 2012. @article{Guan2012, Covert attention modulates saccadic performance, e.g., the abrupt onset of a task-irrelevant visual stimulus grabs attention as measured by a decrease in saccadic reaction time (SRT). The attentional advantage bestowed by the task-irrelevant stimulus is short-lived: SRT is actually longer ~200 ms after the onset of a stimulus than it is when no stimulus appears, known as inhibition of return. The mechanism by which attention modulates saccadic reaction is not well-understood. Here, we propose two possible mechanisms: by selective routing of the visuomotor signal through different pathways (routing hypothesis) or by general modulation of the speed of visuomotor transformation (shifting hypothesis). To test them, we designed a cue gap paradigm in which a 100-ms gap was introduced between the fixation point disappearance and the target appearance to the conventional cued visual reaction time paradigm. The cue manipulated the location of covert attention, and the gap interval resulted in a bimodal distribution of SRT, with an early mode (express saccade) and a late mode (regular saccade). The routing hypothesis predicts changes in the proportion of express saccades vs. regular saccades, whereas the shifting hypothesis predicts a shift of SRT distribution. The addition of the cue had no effect on mean reaction time of express and regular saccades, but it changed the relative proportion of two modes. These results demonstrate that the covert attention modification of the mean SRT is largely attributed to selective routing between visuomotor pathways rather than general modulation of the speed of visuomotor transformation. |
A. Guillaume Saccadic inhibition is accompanied by large and complex amplitude modulations when induced by visual backward masking Journal Article In: Journal of Vision, vol. 12, no. 6, pp. 1–20, 2012. @article{Guillaume2012, Saccadic inhibition refers to the strong temporary decrease in saccadic initiation observed when a visual distractor appears shortly after the onset of a saccadic target. Here, to gain a better understanding of this phenomenon, we assessed whether saccade amplitude changes could accompany these modulations of latency distributions. As previous studies on the saccadic system using visual backward masking–a protocol in which the mask appears shortly after the target–showed latency increases and amplitude changes, we suspected that this could be a condition in which amplitude changes would accompany saccadic inhibition. We show here that visual backward masking produces a strong saccadic inhibition. In addition, this saccadic inhibition was accompanied by large and complex amplitude changes: a first phase of gain decrease occurred before the saccadic inhibition; when saccades reappeared after the inhibition, they were accurate before rapidly entering into a second phase of gain decrease. We observed changes in saccade kinematics that were consistent with the possibility of saccades being interrupted during these two phases of gain decrease. These results show that the onset of a large stimulus shortly after a first one induces the previously reported saccadic inhibition, but also induces a complex pattern of amplitude changes resulting from a dual amplitude perturbation mechanism with fast and slow components. |
Adrian M. Haith; Thomas R. Reppert; Reza Shadmehr Evidence for hyperbolic temporal discounting of reward in control of movements Journal Article In: Journal of Neuroscience, vol. 32, no. 34, pp. 11727–11736, 2012. @article{Haith2012, Suppose that the purpose of a movement is to place the body in a more rewarding state. In this framework, slower movements may increase accuracy and therefore improve the probability of acquiring reward, but the longer durations of slow movements produce devaluation of reward. Here we hypothesize that the brain decides the vigor of a movement (duration and velocity) based on the expected discounted reward associated with that movement. We begin by showing that durations of saccades of varying amplitude can be accurately predicted by a model in which motor commands maximize expected discounted reward. This result suggests that reward is temporally discounted even in timescales of tens of milliseconds. One interpretation of temporal discounting is that the true objective of the brain is to maximize the rate of reward-which is equivalent to a specific form of hyperbolic discounting. A consequence of this idea is that the vigor of saccades should change as one alters the intertrial intervals between movements. We find experimentally that in healthy humans, as intertrial intervals are varied, saccade peak velocities and durations change on a trial-by-trial basis precisely as predicted by a model in which the objective is to maximize the rate of reward. Our results are inconsistent with theories in which reward is discounted exponentially. We suggest that there exists a single cost, rate of reward, which provides a unifying principle that may govern control of movements in timescales of milliseconds, as well as decision making in timescales of seconds to years. |
Katharina Havermann; Robert Volcic; Markus Lappe Saccadic adaptation to moving targets Journal Article In: PLoS ONE, vol. 7, no. 6, pp. e39708, 2012. @article{Havermann2012, Saccades are so called ballistic movements which are executed without online visual feedback. After each saccade the saccadic motor plan is modified in response to post-saccadic feedback with the mechanism of saccadic adaptation. The post-saccadic feedback is provided by the retinal position of the target after the saccade. If the target moves after the saccade, gaze may follow the moving target. In that case, the eyes are controlled by the pursuit system, a system that controls smooth eye movements. Although these two systems have in the past been considered as mostly independent, recent lines of research point towards many interactions between them. We were interested in the question if saccade amplitude adaptation is induced when the target moves smoothly after the saccade. Prior studies of saccadic adaptation have considered intra-saccadic target steps as learning signals. In the present study, the intra-saccadic target step of the McLaughlin paradigm of saccadic adaptation was replaced by target movement, and a post-saccadic pursuit of the target. We found that saccadic adaptation occurred in this situation, a further indication of an interaction of the saccadic system and the pursuit system with the aim of optimized eye movements. |
Frouke Hermens; Robin Walker The site of interference in the saccadic Stroop effect Journal Article In: Vision Research, vol. 73, pp. 10–22, 2012. @article{Hermens2012, In two experiments, the source of competition in the saccadic Stroop effect was investigated. Colored strings of letters were presented at fixation with colored patches in the surround. The task of the participants was to make an eye movement to the patch in the same color as the central string of letters. Three types of cues were compared: Either the string of letters composed a word indicating a direction (the saccadic Stroop condition), or it was a set of arrow signs, or a peripheral stimulus appeared. Whereas response times and saccade errors were similarly influenced by the different types of cues, saccade trajectory deviations away from the cue were found only for peripheral onsets. A second experiment demonstrated that the absence of the curvature effects for direction words was not due to insufficient time to process the words. The results raise doubts on whether the saccadic Stroop effect is effectively an oculomotor effect and could pose a challenge to models of saccade target selection. |
Frouke Hermens; Robin Walker Do you look where I look? Attention shifts and response preparation following dynamic social cues Journal Article In: Journal of Eye Movement Research, vol. 5, no. 5, pp. 1–11, 2012. @article{Hermens2012a, Studies investigating the effects of observing a gaze shift in another person often apply static images of a person with an averted gaze, while measuring response times to a peripheral target. Static images, however, are unlike how we normally perceive gaze shifts of others. Moreover, response times might only reveal the effects of a cue on covert attention and might fail to uncover cueing effects on overt attention or response preparation. We therefore extended the standard paradigm and measured cueing effects formore realistic, dynamic cues (video clips), while comparing response times, saccade direction errors and saccade trajectories. Three cues were compared: A social cue, consisting of a eye-gaze shift, and two socially less relevant cues, consisting of a head tilting movement and a person walking past. Similar results were found for the two centrally presented cues (eye-gaze shift and head tilting) on all three response measures, suggesting that cueing is unaffected by the social status of the cue. Interest- ingly, the cue showing a person walking past showed a dissociation in the direction of the effects on response times on the one hand, and saccade direction errors and latencies on the other hand, suggesting the involvement of two types of (endogenous and exogenous) attention or a distinction between attention and sacadic response preparation. Our results suggest that by using dynamic cues and multiple response measures, properties of cueing can be revealed that would not be found otherwise. |
Frouke Hermens; Johannes Zanker Looking at Op Art: Gaze stability and motion illusions Journal Article In: i-Perception, vol. 3, no. 5, pp. 282–304, 2012. @article{Hermens2012b, Various Op artists have used simple geometrical patterns to create the illusion of motion in their artwork. One explanation for the observed illusion involves retinal shifts caused by small involuntary eye movements that observers make while they try to maintain fixation. Earlier studies have suggested a prominent role of the most conspicuous of these eye movements, small rapid position shifts called microsaccades. Here, we present data that could expand this view with a different interpretation. In three experiments, we recorded participants' eye movements while they tried to maintain visual fixation when being presented with variants of Bridget Riley's Fall, which were manipulated such as to vary the strength of induced motion. In the first two experiments, we investigated the properties of microsaccades for a set of stimuli with known motion strengths. In agreement with earlier observations, microsaccade rates were unaffected by the stimulus pattern and, consequently, the strength of induced motion illusion. In the third experiment, we varied the stimulus pattern across a larger range of parameters and asked participants to rate the perceived motion illusion. The results revealed that motion illusions in patterns resembling Riley's Fall are perceived even in the absence of microsaccades, and that the reported strength of the illusion decreased with the number of microsaccades in the trial. Together, the three experiments suggest that other sources of retinal image instability than microsaccades, such as slow oculomotor drift, should be considered as possible factors contributing to the illusion. |
Lynn Huestegge; Magali Kreutzfeldt Action effects in saccade control Journal Article In: Psychonomic Bulletin & Review, vol. 19, no. 2, pp. 198–203, 2012. @article{Huestegge2012a, According to the ideomotor principle, action preparation involves the activation of associations between actions and their effects. However, there is only sparse research on the role of action effects in saccade control. Here, participants responded to lateralized auditory stimuli with spatially compatible saccades toward peripheral targets (e.g., a rhombus in the left hemifield and a square in the right hemifield). Prior to the imperative auditory stimulus (e.g., a left tone), an irrelevant central visual stimulus was presented that was congruent (e.g., a rhombus), incongruent (e.g., a square), or unrelated (e.g., a circle) to the peripheral saccade target (i.e., the visual effect of the saccade). Saccade targets were present throughout a trial (Experiment 1) or appeared after saccade initiation (Experiment 2). Results showed shorter response times and fewer errors in congruent (vs. incongruent) conditions, suggesting that associations between oculomotor actions and their visual effects play an important role in saccade control. |
Stephanie Jainta; Wolfgang Jaschinski Individual differences in binocular coordination are uncovered by directly comparing monocular and binocular reading conditions Journal Article In: Investigative Ophthalmology & Visual Science, vol. 53, no. 9, pp. 5762–5769, 2012. @article{Jainta2012, PURPOSE: We evaluated systematically binocular coordination during a reading task by comparing binocular and monocular reading, and considering the potential effects of individual heterophoria and eye dominance. METHODS: A total of 13 participants (aged 19-29 years, refractive errors -0.5 to 0.125 diopters [D]) read single sentences in a haploscope while eye movements were measured with an EyeLinkII eyetracker. RESULTS: When reading monocularly, saccade amplitudes increased by 0.04 degrees and first fixation durations became longer by approximately 10 ms. Furthermore, saccade disconjugacies increased, and compensatory vergence drifts during fixation turned into a divergent drift relative to the viewing distance. The vergence angle adjusted for the actual viewing distance became less convergent during monocular reading by 0.5 degrees. Moreover, in participants who were almost orthophoric, only the first fixation duration became longer (by 20 ms) when the reading conditions changed from binocular to monocular. For exophoric participants, all parameters of binocular coordination changed, and first fixation duration decreased by 20 ms. When reading monocularly, no differences between the dominant right eye and the nondominant left eye were found. CONCLUSIONS: Because of obvious differences in binocular coordination between monocular and binocular reading, some vergence adjustments are driven actively by fusional processes. Furthermore, higher demands on these binocular fusional processes can be uncovered only by a detailed evaluation of monocular reading conditions. |
Jean Lorenceau Cursive writing with smooth pursuit eye movements Journal Article In: Current Biology, vol. 22, no. 16, pp. 1506–1509, 2012. @article{Lorenceau2012, The eyes never cease to move: ballistic saccades quickly turn the gaze toward peripheral targets, whereas smooth pursuit maintains moving targets on the fovea where visual acuity is best. Despite the oculomotor system being endowed with exquisite motor abilities, any attempt to generate smooth eye movements against a static background results in saccadic eye movements [1, 2]. Although exceptions to this rule have been reported [3-5], volitional control over smooth eye movements is at best rudimentary. Here, I introduce a novel, temporally modulated visual display, which, although static, sustains smooth eye movements in arbitrary directions. After brief training, participants gain volitional control over smooth pursuit eye movements and can generate digits, letters, words, or drawings at will. For persons deprived of limb movement, this offers a fast, creative, and personal means of linguistic and emotional expression. |
Kevin J. MacKenzie Vergence and accommodation to multiple-image-plane stereoscopic displays: “Real world” responses with practical image-plane separations? Journal Article In: Journal of Electronic Imaging, vol. 21, no. 1, pp. 1–8, 2012. @article{MacKenzie2012, Conventional stereoscopic displays present images on a single focal plane. The resulting mismatch between the stimuli to the eyes' focusing response (accommodation) and to convergence causes fatigue and poor stereo performance. One solution is to distribute image intensity across a number of widely spaced image planes—a technique referred to as depth filtering. Previously, we found this elicits accurate, continuous monocular accommodation responses with image-plane separations as large as 1.1 Diopters (D, the reciprocal of distance in meters), suggesting that a small number of image planes could eliminate vergence-accommodation conflicts over a large range of simulated distances. Evidence exists, however, of systematic differences between accommodation responses to binocular and monocular stimuli when the stimulus to accommodation is degraded, or at an incorrect distance. We examined the minimum image-plane spacing required for accurate accommodation to binocular depth-filtered images. We compared accommodation and vergence responses to changes in depth specified by depth filtering, using image-plane separations of 0.6 to 1.2 D, and equivalent real stimuli. Accommodation responses to real and depth-filtered stimuli were equivalent for image-plane separations of ∼0.6 to 0.9 D, but differed thereafter. We conclude that depth filtering can be used to precisely match accommodation and vergence demand in a practical stereoscopic display. |
Michael B. McCamy; Jorge Otero-Millan; Stephen L. Macknik; Yan Yang; Xoana G. Troncoso; Steven M. Baer; Sharon M. Crook; Susana Martinez-Conde Microsaccadic efficacy and contribution to foveal and peripheral vision Journal Article In: Journal of Neuroscience, vol. 32, no. 27, pp. 9194–9204, 2012. @article{McCamy2012, Our eyes move constantly, even when we try to fixate our gaze. Fixational eye movements prevent and restore visual loss during fixation, yet the relative impact of each type of fixational eye movement remains controversial. For over five decades, the debate has focused on microsaccades, the fastest and largest fixational eye movements. Some recent studies have concluded that microsaccades counteract visual fading during fixation. Other studies have disputed this idea, contending that microsaccades play no significant role in vision. The disagreement stems from the lack of methods to determine the precise effects of microsaccades on vision versus those of other eye movements, as well as a lack of evidence that microsaccades are relevant to foveal vision. Here we developed a novel generalized method to determine the precise quantified contribution and efficacy of human microsaccades to restoring visibility compared with other eye movements. Our results indicate that microsaccades are the greatest eye movement contributor to the restoration of both foveal and peripheral vision during fixation. Our method to calculate the efficacy and contribution of microsaccades to perception can determine the strength of connection between any two physiological and/or perceptual events, providing a novel and powerful estimate of causal influence; thus, we anticipate wide-ranging applications in neuroscience and beyond. |
Robert D. McIntosh; Antimo Buonocore Dissociated effects of distractors on saccades and manual aiming Journal Article In: Experimental Brain Research, vol. 220, no. 3-4, pp. 201–211, 2012. @article{McIntosh2012, The remote distractor effect (RDE) is a robust phenomenon whereby target-directed saccades are delayed by the appearance of a distractor. This effect persists even when the target location is perfectly predictable. The RDE has been studied extensively in the oculomotor domain but it is unknown whether it generalises to other spatially oriented responses. In three experiments, we tested whether the RDE generalises to manual aiming. Experiment 1 required participants to move their hand or eyes to predictable targets presented alone or accompanied by a distractor in the opposite hemifield. The RDE was observed for the eyes but not for the hand. Experiment 2 replicated this dissociation in a more naturalistic task in which eye movements were not constrained during manual aiming. Experiment 3 confirmed the lack of manual RDE across a wider range of distractor delays (0, 50, 100, and 150 ms). Our data imply that the RDE is specific to the oculomotor system, at least for non-foveal distractors. We suggest that the oculomotor RDE reflects competitive interactions between target and distractor representations in the superior colliculus, which are not necessarily shared by manual aiming. |