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2017 |
Wolfgang Einhäuser; Philipp Methfessel; Alexandra Bendixen Newly acquired audio-visual associations bias perception in binocular rivalry Journal Article In: Vision Research, vol. 133, pp. 121–129, 2017. @article{Einhaeuser2017, When distinct stimuli are presented to the two eyes, their mental representations alternate in awareness. Here, such “binocular rivalry” was used to investigate whether audio-visual associations bias visual perception. To induce two arbitrary associations, each between a tone and a grating of a specific color and motion direction, observers were required to respond whenever this combination was presented, but not for other tone-grating combinations. After about 20 min of this induction phase, each of the gratings was presented to one eye to induce rivalry, while either of the two tones or no tone was played. Observers were asked to watch the rivaling stimuli and listen to the tones. The observer's dominant percept was assessed throughout by measuring the optokinetic nystagmus (OKN), whose slow phase follows the direction of the currently dominant grating. We found that perception in rivalry was affected by the concurrently played tone. Results suggest a bias towards the grating that had been associated with the concurrently presented tone and prolonged dominance durations for this grating compared to the other. Numerically, conditions without tone fell in-between for measures of bias and dominance duration. Our data show that a rapidly acquired arbitrary audio-visual association biases visual perception. Unlike previously reported cross-modal interactions in rivalry, this effect can neither be explained by a pure attentional (dual-task) effect, nor does it require a fixed physical or semantic relation between the auditory and visual stimulus. This suggests that audio-visual associations that are quickly formed by associative learning may affect visual representations directly. |
Donatas Jonikaitis; Anna Klapetek; Heiner Deubel Spatial attention during saccade decisions Journal Article In: Journal of Neurophysiology, vol. 118, no. 1, pp. 149–160, 2017. @article{Jonikaitis2017, Behavioral measures of decision making are usually limited to observations of decision outcomes. In the present study, we made use of the fact that oculomotor and sensory selection are closely linked to track oculomotor decision making before oculomotor responses are made. We asked participants to make a saccadic eye movement to one of two memorized target locations and observed that visual sensitivity increased at both the chosen and the non-chosen saccade target locations, with a clear bias towards the chosen target. The time course of changes in visual sensitivity was related to saccadic latency, with the competition between the chosen and non-chosen targets resolved faster before short latency saccades. On error trials, we observed an increased competition between the chosen and non-chosen targets. Moreover, oculomotor selection and visual sensitivity were influenced by top-down and bottom-up factors as well as by selection history and predicted the direction of saccades. Our findings demonstrate that saccade decisions have direct visual consequences and show that decision making can be traced in the human oculomotor system well before choices are made. Our results also indicate a strong association between decision making, saccade target selection and visual sensitivity. |
Kei Kanari; Kiyomi Sakamoto; Hirohiko Kaneko Effect of visual attention on the properties of optokinetic nystagmus Journal Article In: PLoS ONE, vol. 12, no. 4, pp. e0175453, 2017. @article{Kanari2017, It has been demonstrated that optokinetic nystagmus (OKN) gain increases through attention to peripheral motion when the central visual field is occluded. However, how the properties of OKN change when two areas containing motion in different directions are presented in the peripheral visual field is still unclear. In this study, we investigated whether OKN corresponding to the attended motion in the periphery occurred while the observer was maintaining fixation at the center. We presented two areas with different directions of motion arranged on the left and right, top and bottom, or center and surrounding (concentric) areas in the display. Observers counted targets appearing on the attended area in the stimulus to maintain their attention on it. The results indicate that attention enhances the gain and frequency of OKN corresponding to the attended motion even in the case of stimuli having several areas with different directions of motion. |
Min Suk Kang; Sori Kim; Kyoung-Min Lee Peripheral target identification performance modulates eye movements Journal Article In: Vision Research, vol. 133, pp. 81–86, 2017. @article{Kang2017a, We often shift our eyes to an interesting stimulus, but it is important to inhibit that eye movement in some environments (e.g., a no-look pass in basketball). Here, we investigated participants' ability to inhibit eye movements when they had to process a peripheral target with a requirement to maintain strict fixation. An array of eight letters composed of four characters was briefly presented and a directional cue was centrally presented to indicate the target location. The stimulus onset asynchrony (SOA) between the cue and the stimulus array was chosen from six values, consisting of pre-cue conditions (−400 and −200 ms), a simultaneous cue condition (0 ms), and post-cue conditions (200, 400, and 800 ms). We found the following: 1) participants shifted their eyes toward the cued location even though the stimulus array was absent at the onset of eye movements, but the eye movement amplitude was smaller than the actual location of the target; 2) eye movements occurred approximately 150 ms after the onset of stimulus array in the pre-cue conditions and 250 ms after cue onset in the simultaneous and post-cue conditions; and 3) eye movement onsets were delayed and their amplitudes were smaller in correct trials than incorrect trials. These results indicate that the inhibitory process controlling eye movements also compete for cognitive resources like other cognitive processes. |
Devin H. Kehoe; Mazyar Fallah Rapid accumulation of inhibition accounts for saccades curved away from distractors Journal Article In: Journal of Neurophysiology, vol. 118, no. 2, pp. 832–844, 2017. @article{Kehoe2017, Saccades curved toward a distractor are accompanied by a burst of neuronal activation at the distractor locus in the intermediate layers of the superior colliculus (SCi) ~30 ms before the initiation of a saccade. Although saccades curve away from inactivated SCi loci, whether inhibition is restricted to a similar critical epoch for saccades curved away from a distractor remains unclear. We examined this possibility by modeling human saccade curvature as a function of the time between onset of a task irrelevant luminance- or color-modulated distractor and initiation of an impending saccade, referred to as saccade distractor onset asynchrony (SDOA). Our results demonstrated that 70 ms of luminance-modulated distractor processing or 90 ms of color-modulated distractor processing was required to modulate saccade trajectories. As these behavioral, feature-based differences were temporally consistent with the cortically mediated neurophysiological differences in visual onset latencies between luminance and color stimuli observed in the oculomotor and visual system, this method provides a noninvasive means to estimate the timing of peak activation in the oculomotor system. As such, we modeled SDOA functions separately for saccades curved toward and away from distractors and observed that a similar temporal process determined the magnitude of saccade curvatures in both contexts, suggesting that saccades deviate away from a distractor due to a rapid accumulation of inhibition in the critical epoch before saccade initiation. |
Philipp Kreyenmeier; Jolande Fooken; Miriam Spering Context effects on smooth pursuit and manual interception of a disappearing target Journal Article In: Journal of Neurophysiology, vol. 118, no. 1, pp. 404–415, 2017. @article{Kreyenmeier2017, In our natural environment, we interact with moving objects that are surrounded by richly textured, dynamic visual contexts. Yet most laboratory studies on vision and movement show visual objects in front of uniform gray backgrounds. Context effects on eye movements have been widely studied, but it is less well known how visual contexts affect hand movements. Here we ask whether eye and hand movements integrate motion signals from target and context similarly or differently, and whether context effects on eye and hand change over time. We developed a track-intercept task requiring participants to track the initial launch of a moving object (" ball ") with smooth pursuit eye movements. The ball disappeared after a brief presentation, and participants had to intercept it in a designated " hit zone. " In two experiments (n ϭ 18 human observers each), the ball was shown in front of a uniform or a textured background that either was stationary or moved along with the target. Eye and hand movement latencies and speeds were similarly affected by the visual context, but eye and hand interception (eye position at time of interception, and hand interception timing error) did not differ significantly between context conditions. Eye and hand interception timing errors were strongly correlated on a trial-by-trial basis across all context conditions, highlighting the close relation between these responses in manual interception tasks. Our results indicate that visual contexts similarly affect eye and hand movements but that these effects may be short-lasting, affecting movement trajectories more than movement end points. |
Elke B. Lange; Fabian Zweck; Petra Sinn Microsaccade-rate indicates absorption by music listening Journal Article In: Consciousness and Cognition, vol. 55, pp. 59–78, 2017. @article{Lange2017, The power of music is a literary topos, which can be attributed to intense and personally significant experiences, one of them being the state of absorption. Such phenomenal states are difficult to grasp objectively. We investigated the state of musical absorption by using eye tracking. We utilized a load related definition of state absorption: multimodal resources are committed to create a unified representation of music. Resource allocation was measured indirectly by microsaccade rate, known to indicate cognitive processing load. We showed in Exp. 1 that microsaccade rate also indicates state absorption. Hence, there is cross-modal coupling between an auditory aesthetic experience and fixational eye movements. When removing the fixational stimulus in Exp. 2, saccades are no longer generated upon visual input and the cross-modal coupling disappeared. Results are interpreted in favor of the load hypothesis of microsaccade rate and against the assumption of general slowing by state absorption. |
Jeyeon Lee; Hoseok Choi; Seho Lee; Baek Hwan Cho; Kyoung-ha Ahn; In Young Kim; Kyoung-Min Lee; Dong-Pyo Jang Decoding saccadic directions using epidural ECoG in non-human primates Journal Article In: Journal of Korean Medical Science, vol. 32, no. 8, pp. 1243–1250, 2017. @article{Lee2017, A brain-computer interface (BCI) can be used to restore some communication as an alternative interface for patients suffering from locked-in syndrome. However, most BCI systems are based on SSVEP, P300, or motor imagery, and a diversity of BCI protocols would be needed for various types of patients. In this paper, we trained the choice saccade (CS) task in 2 non-human primate monkeys and recorded the brain signal using an epidural electrocorticogram (eECoG) to predict eye movement direction. We successfully predicted the direction of the upcoming eye movement using a support vector machine (SVM) with the brain signals after the directional cue onset and before the saccade execution. The mean accuracies were 80% for 2 directions and 43% for 4 directions. We also quantified the spatial-spectro-temporal contribution ratio using SVM recursive feature elimination (RFE). The channels over the frontal eye field (FEF), supplementary eye field (SEF), and superior parietal lobule (SPL) area were dominantly used for classification. The α-band in the spectral domain and the time bins just after the directional cue onset and just before the saccadic execution were mainly useful for prediction. A saccade based BCI paradigm can be projected in the 2D space, and will hopefully provide an intuitive and convenient communication platform for users. |
Rebekka Lencer; Annegret Meermeier; Karen Silling; Svenja Gremmler; Markus Lappe Instability of visual error processing for sensorimotor adaptation in schizophrenia Journal Article In: European Archives of Psychiatry and Clinical Neuroscience, vol. 267, no. 3, pp. 237–244, 2017. @article{Lencer2017, Saccadic adaptation can be used to study disturbances of sensory processing and motor learning. We investigated whether patients with schizophrenia can adjust saccadic amplitudes to account for an increase in visual error while the saccade is in flight, and whether they transfer this change to a visuo-manual localization task. Fourteen patients (mean 37.1 years) and 14 healthy controls (mean 35.1 years) performed 200 adaptation trials of 10° with target shifts of 4° in the outward direction. We determined the percent amplitude change during adaptation and adaptation speed. In addition, subjects localized a stimulus that was flashed 50 ms after saccade target onset to measure the transfer of change in visual space perception to visuo-manual coordination. Eye movements were recorded at 1000 Hz. Saccade amplitudes increased over adapta- tion trials by 11 % (p < 0.001) similarly in both groups. Amplitude variability during adaptation was higher in patients (1.06° ± 0.32°) than in controls (0.71° ± 0.14°; p = 0.001), while adaptation speed was slower in patients (0.02 ± 0.03) than in controls (0.11 ± 0.11; p = 0.01). Other pre- and post-adaptation saccade metrics did not differ between groups. The adaptation process shifted localization of the flashed target in the adaptation direction simi- larly in both groups. The use of error signals for the internal recalibration of sensorimotor systems and the transfer of this recalibration to visual space perception appear basically unimpaired in schizophrenia. Higher amplitude variability in patients suggests a certain instability of saccadic control in cerebellar systems. Patients seem to rely on visual error processing in frontal circuitry, resulting in slower adaptation speeds, despite unimpaired adaptation strength. |
Rebekka Lencer; L. J. Mills; N. Alliey-Rodriguez; R. Shafee; A. M. Lee; James L. Reilly; Andreas Sprenger; Jennifer E. McDowell; S. A. McCarroll; Matcheri S. Keshavan; Godfrey D. Pearlson; Carol A. Tamminga; Brett A. Clementz; Elliot S. Gershon; John A. Sweeney; J. R. Bishop Genome-wide association studies of smooth pursuit and antisaccade eye movements in psychotic disorders: findings from the B-SNIP study Journal Article In: Translational Psychiatry, vol. 7, pp. e1249, 2017. @article{Lencer2017a, Eye movement deviations, particularly deficits of initial sensorimotor processing and sustained pursuit maintenance, and antisaccade inhibition errors, are established intermediate phenotypes for psychotic disorders. We here studied eye movement measures of 849 participants from the Bipolar-Schizophrenia Network on Intermediate Phenotypes (B-SNIP) study (schizophrenia N = 230, schizoaffective disorder N = 155, psychotic bipolar disorder N = 206 and healthy controls N = 258) as quantitative phenotypes in relation to genetic data, while controlling for genetically derived ancestry measures, age and sex. A mixed-modeling genome-wide association studies approach was used including ~ 4.4 million genotypes (PsychChip and 1000 Genomes imputation). Across participants, sensorimotor processing at pursuit initiation was significantly associated with a single nucleotide polymorphism in IPO8 (12p11.21 |
Maria J. Barraza-Bernal; Katharina Rifai; Siegfried Wahl Transfer of an induced preferred retinal locus of fixation to everyday life visual tasks Journal Article In: Journal of Vision, vol. 17, no. 14, pp. 2, 2017. @article{BarrazaBernal2017a, Subjects develop a preferred retinal locus of fixation (PRL) under simulation of central scotoma. If systematic relocations are applied to the stimulus position, PRLs manifest at a location in favor of the stimulus relocation. The present study investigates whether the induced PRL is transferred to important visual tasks in daily life, namely pursuit eye movements, signage reading, and text reading. Fifteen subjects with normal sight participated in the study. To develop a PRL, all subjects underwent a scotoma simulation in a prior study, where five subjects were trained to develop the PRL in the left hemifield, five different subjects on the right hemifield, and the remaining five subjects could naturally chose the PRL location. The position of this PRL was used as baseline. Under central scotoma simulation, subjects performed a pursuit task, a signage reading task, and a reading-text task. In addition, retention of the behavior was also studied. Results showed that the PRL position was transferred to the pursuit task and that the vertical location of the PRL was maintained on the text reading task. However, when reading signage, a function-driven change in PRL location was observed. In addition, retention of the PRL position was observed over weeks and months. These results indicate that PRL positions can be induced and may further transferred to everyday life visual tasks, without hindering function-driven changes in PRL position. |
Maria J. Barraza-Bernal; Katharina Rifai; Siegfried Wahl A preferred retinal location of fixation can be induced when systematic stimulus relocations are applied Journal Article In: Journal of Vision, vol. 17, no. 2, pp. 1–13, 2017. @article{BarrazaBernal2017b, Patients with central vision loss obtain visual information by fixating on an object eccentrically with a preferred retinal locus of fixation (PRL). Patients do not always choose the most efficient PRL position, and as a consequence, visual performance is not always fully exploited. This study investigates whether PRLs can be induced by applying systematic stimulus relocations. The PRL was trained using a central scotoma simulation in 15 healthy subjects. They performed different visual tasks during four sessions, after which their reading performance was evaluated. In five subjects the stimulus was relocated to the left hemifield whenever a saccade would place the stimulus on the opposite hemifield. In five different subjects the relocation was inversed: The stimulus was located in the right hemifield. The relocation was 7.5° of visual angle and it was applied horizontally. Five additional subjects naturally chose the PRL location. They were used as the control group to evaluate the development of a PRL. After training, subjects performed visual search tasks on static stimuli. Evaluation after training showed that systematic stimulus relocations can be used to influence the development of the PRL. These results might be significant for the development of training strategies for the visually impaired. |
Joachim Bellet; Chih-Yang Chen; Ziad M. Hafed Sequential hemifield gating of alpha and beta behavioral performance oscillations after microsaccades Journal Article In: Journal of Neurophysiology, vol. 118, pp. 2789–2805, 2017. @article{Bellet2017, Microsaccades are tiny saccades that occur during gaze fixation. Even though visual processing has been shown to be strongly modulated close to the time of microsaccades, both at central and peripheral eccentricities, it is not clear how these eye movements might influence longer term fluctuations in brain activity and behavior. Here we found that visual processing is significantly affected and, in a rhythmic manner, even several hundreds of milliseconds after a microsaccade. Human visual detection efficiency, as measured by reaction time, exhibited coherent rhythmic oscillations in the ? - and ? -frequency bands for up to ~650–700 ms after a microsaccade. Surprisingly, the oscillations were sequentially pulsed across visual hemifields relative to microsaccade direction, first occurring in the same hemifield as the movement vector for ~400 ms and then the opposite. Such pulsing also affected perceptual detection performance. Our results suggest that visual processing is subject to long-lasting oscillations that are phase locked to microsaccade generation, and that these oscillations are dependent on microsaccade direction. |
Alessandro Benedetto; M. Concetta Morrone Saccadic suppression is embedded within extended oscillatory modulation of sensitivity Journal Article In: Journal of Neuroscience, vol. 37, no. 13, pp. 3661–3670, 2017. @article{Benedetto2017, Action and perception are intimately coupled systems. One clear case is saccadic suppression, the reduced visibility around the time of saccades, which is important in mediating visual stability; another is the oscillatory modulation of visibility synchronized with hand action. To suppress effectively the spurious retinal motion generated by the eye movements, it is crucial that saccadic suppression and saccadic onset be temporally synchronous. However, the mechanisms that determine this temporal synchrony are unknown. We investigated the effect of saccades on contrast discrimination sensitivity over a long period stretching over >1 s before and after saccade execution. Human subjects made horizontal saccades at will to two stationary saccadic targets separated by 20°. At a random interval, a brief Gabor patch was displayed between the two fixations in either the upper or lower visual field and the subject had to detect its location. Strong saccadic suppression was measured between -50 and 50 ms from saccadic onset. However, the suppression was systematically embedded in a trough of oscillations of contrast sensitivity that fluctuated rhythmically in the delta range (at ∼3 Hz), commencing ∼1 s before saccade execution and lasting for up to 1 s after the saccade. The results show that saccadic preparation and visual sensitivity oscillations are coupled and the coupling might be instrumental in temporally aligning the initiation of the saccade with the visual suppression. |
Katharina Bey; Lisa Kloft; Leonhard Lennertz; Rosa Grützmann; Stephan Heinzel; Christian Kaufmann; Julia Klawohn; Anja Riesel; Inga Meyhöfer; Norbert Kathmann; Michael Wagner Volitional saccade performance in a large sample of patients with obsessive-compulsive disorder and unaffected first-degree relatives Journal Article In: Psychophysiology, vol. 54, no. 9, pp. 1284–1294, 2017. @article{Bey2017, Recent evidence indicates that patients with obsessive-compulsive disorder (OCD) as well as their unaffected first-degree relatives show deficits in the volitional control of saccades, suggesting that volitional saccade performance may constitute an endophenotype of OCD. Here, we aimed to replicate and extend these findings in a large, independent sample. One hundred and fifteen patients with OCD, 103 healthy comparison subjects without a family history of OCD, and 31 unaffected first-degree relatives of OCD patients were examined using structured clinical interviews and performed a volitional saccade task as well as a prosaccade task. In contrast to previous reports, neither patients nor relatives showed impairments in the performance of volitional saccades compared to healthy controls. Notably, medicated patients did not differ from nonmedicated patients, and there was no effect of depressive comorbidity. Additional analyses investigating correlations between saccade performance and OCD symptom dimensions yielded no significant associations. In conclusion, the present results do not support the notion that volitional saccade execution constitutes an endophenotype of OCD. Possible explanations for inconsistencies with previous studies are discussed. |
Jutta Billino; Jürgen Hennig; Karl R. Gegenfurtner In: Vision Research, vol. 141, no. 170-180, pp. 170–180, 2017. @article{Billino2017, The neural circuits involved in oculomotor control are well described; however, neuromodulation of eye movements is still hardly understood. Memory guided saccades have been extensively studied and in particular neurophysiological evidence from monkey studies points to a crucial functional role of prefrontal dopamine activity. We exploited individual differences in dopamine regulation due to the well established COMT (catechol-O-methyltransferase) Val158Met polymorphism to explore the link between prefrontal dopamine activity and memory guided saccades in healthy subjects. The COMT genotype is thought to modulate dopamine metabolism in prefrontal cortex producing differences in dopamine availability. We investigated memory guided saccades in 111 healthy subjects and determined individual genotypes. Accuracy and precision were reduced in subjects with putatively higher prefrontal dopamine levels. In contrast, we found no modulation of saccade parameters by genotype in a visually guided control task. Our results suggest that increased dopamine activity can have a detrimental effect on saccades that rely on spatial memory representations. Although these findings await replication in larger and more diverse sample sizes, they provide persuasive support that specific oculomotor parameters are sensitive to dopaminergic variation in healthy subjects and add to a better understanding of how dopamine modulates saccadic control. |
Paola Binda; Claudia Lunghi Short-term monocular deprivation enhances physiological pupillary oscillations Journal Article In: Neural Plasticity, vol. 2017, pp. 6724631, 2017. @article{Binda2017, Short-term monocular deprivation alters visual perception in adult humans, increasing the dominance of the deprived eye, for example, as measured with binocular rivalry. This formofplasticitymay depend upon the inhibition/excitation balance in the visual cortex. Recent work suggests that cortical excitability is reliably tracked by dilations and constrictions ofthe pupils ofthe eyes. Here, we ask whether monocular deprivation produces a systematic change ofpupil behavior, as measured at rest, that is independent of the change of visual perception. During periods of minimal sensory stimulation (in the dark) and task requirements (minimizing body and gaze movements), slow pupil oscillations, “hippus,” spontaneously appear. We find that hippus amplitude increases after monocular deprivation, with larger hippus changes in participants showing larger ocular dominance changes (measured by binocular rivalry). This tight correlation suggests that a single latent variable explains both the change of ocular dominance and hippus. We speculate that the neurotransmitter norepinephrine may be implicated in this phenomenon, given its important role in both plasticity and pupil control. On the practical side, our results indicate that measuring the pupil hippus (a simple and short procedure) provides a sensitive index of the change of ocular dominance induced by short-term monocular deprivation, hence a proxy for plasticity. |
Paul J. Boon; Artem V. Belopolsky Eye abduction reduces but does not eliminate competition in the oculomotor system Journal Article In: Journal of Vision, vol. 17, no. 5, pp. 1–10, 2017. @article{Boon2017, Although it is well established that there is a tight coupling between covert attention and the eye movement system there is an ongoing controversy whether this relationship is functional. Previous studies demonstrated that disrupting the ability to execute an eye movement interferes with the allocation of covert attention. One technique that prevents the execution of an eye movement involves the abduction of the eye in the orbit while presenting the stimuli outside of the effective oculomotor range (Craighero, Nascimben, & Fadiga, 2004). Although eye abduction is supposed to disrupt activation of the oculomotor program responsible for the shift of covert attention, this crucial assumption has never been tested experimentally. In the present study we used saccadic curvature to examine whether eye abduction eliminates the target-distractor competition in the oculomotor system. We experimentally reduced the ability to execute saccades by abducting the eye by 308 (monocular vision). This way the peripheral part of the temporal hemifield was located outside the oculomotor range. Participants made a vertical eye movement while on some trials a distractor was shown either inside or outside of the oculomotor range. The curvature away from distractors located outside the oculomotor range was reduced, but not completely eliminated. This confirms that eye abduction influences the activation of the oculomotor program, but points to the fact that other forms of motor planning, such as head movements are also represented in the oculomotor system. The results are in line with the idea that covert attention is an emerging property of movement planning, but is not restricted to saccade planning. |
Mathieu Boulanger; Guillaume Giraudet; Jocelyn Faubert In: PLoS ONE, vol. 12, no. 3, pp. e0173678, 2017. @article{Boulanger2017, Humans routinely scan their environment for useful information using saccadic eye movements and/or coordinated movements of the eyes and other body segments such the head and the torso. Most previous eye movement studies were conducted with seated subject and showed that single saccades and sequences of saccades (e.g. double-step saccades) made to briefly flashed stimuli were equally accurate and precise. As one can easily appreciate, most gaze shifts performed daily by a given person are not produced from a seated position, but rather from a standing position either as subjects perform an action from an upright stance or as they walk from one place to another. In the experiments presented here, we developed a new dual-task paradigm in order to study the interaction between the gaze control system and the postural system. Healthy adults (n = 12) were required to both maintain balance and produce accurate single-step and double-step eye saccades from a standing position. Visually-induced changes in head sway were evoked using wide-field background stimuli that either moved in the mediolateral direction or in the anteroposterior direction. We found that, as in the seated condition, single- and double-step saccades were very precise and accurate when made from a standing position, but that a tighter control of head sway was necessary in the more complex double-step saccades condition for equivalent results to be obtained. Our perturbation results support the "common goal" hypothesis that state that if necessary, as was the case during the more complex oculomotor task, context-dependent modulations of the postural system can be triggered to reduced instability and therefore support the accomplishment of a suprapostural goal. |
Eric O. Boyer; Arthur Portron; Frederic Bevilacqua; Jean Lorenceau Continuous auditory feedback of eye movements: An exploratory study toward improving oculomotor control Journal Article In: Frontiers in Neuroscience, vol. 11, pp. 197, 2017. @article{Boyer2017, © 2017 Boyer, Portron, Bevilacqua and Lorenceau. As eye movements are mostly automatic and overtly generated to attain visual goals, individuals have a poor metacognitive knowledge of their own eye movements. We present an exploratory study on the effects of real-time continuous auditory feedback generated by eye movements. We considered both a tracking task and a production task where smooth pursuit eye movements (SPEM) can be endogenously generated. In particular, we used a visual paradigm which enables to generate and control SPEM in the absence of a moving visual target. We investigated whether real-time auditory feedback of eye movement dynamics might improve learning in both tasks, through a training protocol over 8 days. The results indicate that real-time sonification of eye movements can actually modify the oculomotor behavior, and reinforce intrinsic oculomotor perception. Nevertheless, large inter-individual differences were observed preventing us from reaching a strong conclusion on sensorimotor learning improvements. |
Doris I. Braun; Alexander C. Schütz; Karl R. Gegenfurtner Visual sensitivity for luminance and chromatic stimuli during the execution of smooth pursuit and saccadic eye movements Journal Article In: Vision Research, vol. 136, pp. 57–69, 2017. @article{Braun2017, Visual sensitivity is dynamically modulated by eye movements. During saccadic eye movements, sensitivity is reduced selectively for low-spatial frequency luminance stimuli and largely unaffected for high-spatial frequency luminance and chromatic stimuli (Nature 371 (1994), 511–513). During smooth pursuit eye movements, sensitivity for low-spatial frequency luminance stimuli is moderately reduced while sensitivity for chromatic and high-spatial frequency luminance stimuli is even increased (Nature Neuroscience, 11 (2008), 1211–1216). Since these effects are at least partly of different polarity, we investigated the combined effects of saccades and smooth pursuit on visual sensitivity. For the time course of chromatic sensitivity, we found that detection rates increased slightly around pursuit onset. During saccades to static and moving targets, detection rates dropped briefly before the saccade and reached a minimum at saccade onset. This reduction of chromatic sensitivity was present whenever a saccade was executed and it was not modified by subsequent pursuit. We also measured contrast sensitivity for flashed high- and low-spatial frequency luminance and chromatic stimuli during saccades and pursuit. During saccades, the reduction of contrast sensitivity was strongest for low-spatial frequency luminance stimuli (about 90%). However, a significant reduction was also present for chromatic stimuli (about 58%). Chromatic sensitivity was increased during smooth pursuit (about 12%). These results suggest that the modulation of visual sensitivity during saccades and smooth pursuit is more complex than previously assumed. |
Frank Bremmer; Jan Churan; Markus Lappe Heading representations in primates are compressed by saccades Journal Article In: Nature Communications, vol. 8, pp. 920, 2017. @article{Bremmer2017, Perceptual illusions help to understand how sensory signals are decoded in the brain. Here we report that the opposite approach is also applicable, i.e., results from decoding neural activity from monkey extrastriate visual cortex correctly predict a hitherto unknown per- ceptual illusion in humans. We record neural activity from monkey medial superior temporal (MST) and ventral intraparietal (VIP) area during presentation of self-motion stimuli and concurrent reflexive eye movements. A heading-decoder performs veridically during slow eye movements. During fast eye movements (saccades), however, the decoder erroneously reports compression of heading toward straight ahead. Functional equivalents of macaque areas MST and VIP have been identified in humans, implying a perceptual correlate (illusion) of this perisaccadic decoding error. Indeed, a behavioral experiment in humans shows that perceived heading is perisaccadically compressed toward the direction of gaze. Response properties of primate areas MST and VIP are consistent with being the substrate of the newly described visual illusion. |
Antimo Buonocore; Alessio Fracasso; David Melcher Pre-saccadic perception: Separate time courses for enhancement and spatial pooling at the saccade target Journal Article In: PLoS ONE, vol. 12, no. 6, pp. e0178902, 2017. @article{Buonocore2017, We interact with complex scenes using eye movements to select targets of interest. Studies have shown that the future target of a saccadic eye movement is processed differently by the visual system. A number of effects have been reported, including a benefit for perceptual performance at the target (“enhancement”), reduced influences of backward masking (“un-masking”), reduced crowding (“un-crowding”) and spatial compression towards the saccade target. We investigated the time course of these effects by measuring orientation discrimination for targets that were spatially crowded or temporally masked. In four experiments, we varied the target-flanker distance, the presence of forward/backward masks, the orientation of the flankers and whether participants made a saccade. Masking and randomizing flanker orientation reduced performance in both fixation and saccade trials. We found a small improvement in performance on saccade trials, compared to fixation trials, with a time course that was consistent with a general enhancement at the saccade target. In addition, a decrement in performance (reporting the average flanker orientation, rather than the target) was found in the time bins nearest saccade onset when random oriented flankers were used, consistent with spatial pooling around the saccade target. We did not find strong evidence for un-crowding. Overall, our pattern of results was consistent with both an early, general enhancement at the saccade target and a later, peri-saccadic compression/pooling towards the saccade target. |
Antimo Buonocore; Simran Purokayastha; Robert D. McIntosh Saccade reorienting is facilitated by pausing the oculomotor program Journal Article In: Journal of Cognitive Neuroscience, vol. 29, no. 12, pp. 2068–2080, 2017. @article{Buonocore2017a, As we look around the world, selecting our targets, competing events may occur at other locations. Depending on current goals, the viewer must decide whether to look at new events or to ignore them. Two experimental paradigms formalize these response options: double-step saccades and saccadic inhibition. In the first, the viewer must reorient to a newly appearing target; in the second, they must ignore it. Until now, the relationship between reorienting and inhibition has been unexplored. In three experiments, we found saccadic inhibition ∼100 msec after a new target onset, regardless of the task instruction. Moreover, if this automatic inhibition is boosted by an irrelevant flash, reorienting is facilitated, suggesting that saccadic inhibition plays a crucial role in visual behavior, as a bottom–up brake that buys the time needed for decisional processes to act. Saccadic inhibition may be a ubiquitous pause signal that provides the flexibility for voluntary behavior to emerge. |
Mrinmoy Chakrabarty; Tamami Nakano; Shigeru Kitazawa Short-latency allocentric control of saccadic eye movements Journal Article In: Journal of Neurophysiology, vol. 117, no. 1, pp. 376–387, 2017. @article{Chakrabarty2017, It is generally accepted that the neural circuits that are implicated in saccade control use retinotopically coded target locations. However, several studies have revealed that nonretinotopic representation is also used. This idea raises a question about whether nonretinotopic coding is egocentric (head or body centered) or allocentric (environment centered). In the current study, we hypothesized that allocentric coding may play a crucial role in immediate saccade control. To test this hypothesis, we used an immediate double-step saccade task toward two sequentially flashed targets with a frame in the background, and we examined whether the end point of the second saccade was affected by a transient shift of the background that participants were told to ignore. When the background was shifted transiently upward (or downward) during the flash of the second target, the second saccade generally erred the target downward (or upward), which was in the direction opposite to the shift of the background. The effect on the second saccade became significant within 150 ms after the frame was presented for decoding and was built up for 200 ms thereafter. When the second saccade was not adjusted, a small, corrective saccade followed within 300 ms. The effect scaled linearly with the shift size up to 3° for a noncorrective second saccade and up to 6° for a corrective saccade. The present results show that an allocentric location of a target is rapidly represented by the brain and used for controlling saccades. NEW & NOTEWORTHY We found that the saccade end point was shifted from the actual target position toward the direction expected from allocentric coding when a large frame in the background was transiently shifted during the period of target presentation. The effect occurred within 150 ms. The present study provides direct evidence that the brain rapidly uses allocentric coding of a target to control immediate saccades. |
Romain Chaumillon; Nadia Alahyane; Patrice Senot; Judith Vergne; Christelle Lemoine-Lardennois; Jean Blouin; Karine Doré-Mazars; Alain Guillaume; Dorine Vergilino-Perez Asymmetry in visual information processing depends on the strength of eye dominance Journal Article In: Neuropsychologia, vol. 96, pp. 129–136, 2017. @article{Chaumillon2017, Unlike handedness, sighting eye dominance, defined as the eye unconsciously chosen when performing monocular tasks, is very rarely considered in studies investigating cerebral asymmetries. We previously showed that sighting eye dominance has an influence on visually triggered manual action with shorter reaction time (RT) when the stimulus appears in the contralateral visual hemifield with respect to the dominant eye (Chaumillon et al. 2014). We also suggested that eye dominance may be more or less pronounced depending on individuals and that this eye dominance strength could be evaluated through saccadic peak velocity analysis in binocular recordings (Vergilino-Perez et al. 2012). Based on these two previous studies, we further examine here whether the strength of the eye dominance can modulate the influence of this lateralization on manual reaction time. Results revealed that participants categorized as having a strong eye dominance, but not those categorized as having a weak eye dominance, exhibited the difference in RT between the two visual hemifields. This present study reinforces that the analysis of saccade peak velocity in binocular recordings provides an effective tool to better categorize the eye dominance. It also shows that the influence of eye dominance in visuo-motor tasks depends on its strength. Our study also highlights the importance of considering the strength of eye dominance in future studies dealing with brain lateralization. |
Tomer Elbaum; Michael Wagner; Assaf Botzer Cyclopean , dominant , and non-dominant gaze tracking for smooth pursuit gaze interaction Journal Article In: Journal of Eye Movement Research, vol. 10, no. 1, pp. 1–14, 2017. @article{Elbaum2017, User-centered design questions in gaze interfaces have been explored in multitude empirical investigations. Interestingly, the question of what eye should be the input device has never been studied. We compared tracking accuracy between the "cyclopean" (i.e., mid-point between eyes) dominant and non-dominant eye. In two experiments, participants performed tracking tasks. In Experiment 1, participants did not use a crosshair. Results showed that mean distance from target was smaller with cyclopean than with dominant or non-dominant eyes. In Experiment 2, participants controlled a crosshair with their cyclopean, dominant and non-dominant eye intermittently and had to align the crosshair with the target. Overall tracking accuracy was highest with cyclopean eye, yet similar between cyclopean and dominant eye in the second half of the experiment. From a theoretical viewpoint, our findings correspond with the cyclopean eye theory of egocentric direction and provide indication for eye dominance, in accordance with the hemispheric laterality approach. From a practical viewpoint, we show that what eye to use as input should be a design consideration in gaze interfaces. |
Vivian Eng; Alfred Lim; Simon Kwon; Su Ren Gan; S. Azrin Jamaluddin; Steve M. J. Janssen; Jason Satel Stimulus-response incompatibility eliminates inhibitory cueing effects with saccadic but not manual responses Journal Article In: Attention, Perception, and Psychophysics, vol. 79, no. 4, pp. 1097–1106, 2017. @article{Eng2017, There are thought to be two forms of inhibition of return (IOR) depending on whether the oculomotor system is activated or suppressed. When saccades are allowed, output-based IOR is generated, whereas input-based IOR arises when saccades are prohibited. In a series of 4 experiments, we mixed or blocked compatible and incompatible trials with saccadic or manual responses to investigate whether cueing effects would follow the same pattern as those observed with more traditional peripheral onsets and central arrows. In all experiments, an uninformative cue was displayed, followed by a cue-back stimulus that was either red or green, indicating whether a compatible or incompatible response was required. The results showed that IOR was indeed observed for compatible responses in all tasks, whereas IOR was eliminated for incompatible trials-but only with saccadic responses. These findings indicate that the dissociation between input- and output-based forms of IOR depends on more than just oculomotor activation, providing further support for the existence of an inhibitory cueing effect that is distinct to the manual response modality. |
Ian M. Erkelens; William R. Bobier Asymmetries between convergence and divergence reveal tonic vergence is dependent upon phasic vergence function Journal Article In: Journal of Vision, vol. 17, no. 5, pp. 1–16, 2017. @article{Erkelens2017, Horizontal vergence eye movements are controlled by two processes, phasic and slow-tonic. Slow-tonic responses are hypothesized to be stimulated by the faster, pulse-step neural output of the phasic system. This suggests that the general behavior of each system should be similar; however, this relationship has yet to be investigated directly. We characterize the relationship between phasic and tonic vergence by quantifying directional asymmetries in the response properties of each mechanism to the same disparity amplitudes. Four subjects viewed symmetric steps in disparity dichoptically at 40 cm while eye movements were recorded with infrared oculography. First- and secondorder phasic and slow-tonic convergence response properties increased linearly with disparity demand (p < 0.01), whereas divergence responses did not (p > 0.05). Phasic divergence responses were slower than convergence (p = 0.012) and were associated with a higher frequency of saccades (p < 0.001). The average rate of slow-tonic change was correlated to the average peak velocity of phasic vergence at the same vergence demand in both directions |
Moritz Feil; Barbara Moser; Mathias Abegg The interaction of pupil response with the vergence system Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 255, no. 11, pp. 2247–2253, 2017. @article{Feil2017, PURPOSE: A gaze shift from a target at distance to a target at near leads to pupillary constriction. The regulation of this pupillary near response is ill known. We investigated the impact of accommodation, convergence, and proximity on the pupillary diameter. METHODS: We recorded pupil size and vergence eye movements with the use of an infrared eye tracker. We determined the pupillary response in four conditions: (1) after a gaze shift from far to near without accommodation, (2) after a gaze shift from far to near with neither accommodation nor convergence, (3) after accommodation alone, and (4) after accommodation with convergence without a gaze shift to near. These responses were compared to the pupil response of a full near response and to a gaze shift from one far target to another. RESULTS: We found a reliable pupillary near response. The removal of both accommodation and convergence in gaze shift from far to near abolished the pupillary near response. Accommodation alone did not induce pupillary constriction, while convergence and accommodation together induced a pupil response similar to the full near response. CONCLUSIONS: The main trigger for the pupillary response seems to be convergence. Neither accommodation nor proximity alone induce a significant pupillary constriction. This suggests that the miosis of the near triad is closely coupled to the vergence system rather than being independently regulated. |
Edward G. Freedman; Sophie Molholm; Michael J. Gray; Daniel Belyusar; John J. Foxe Saccade adaptation deficits in developmental dyslexia suggest disruption of cerebellar-dependent learning Journal Article In: Journal of Neurodevelopmental Disorders, vol. 9, no. 1, pp. 1–8, 2017. @article{Freedman2017, Background: Estimates of the prevalence of developmental dyslexia in the general population range from 5% to as many as 10%. Symptoms include reading, writing, and language deficits, but the severity and mix of symptoms can vary widely across individuals. In at least some people with dyslexia, the structure and function of the cerebellum may be disordered. Saccadic adaptation requires proper function of the cerebellum and brainstem circuitry and might provide a simple, noninvasive assay for early identification and sub-phenotyping in populations of children who may have dyslexia. Methods: Children between the ages of 7 and 15 served as participants in this experiment. Fifteen had been diagnosed with developmental dyslexia and an additional 15 were typically developing children. Five of the participants diagnosed with dyslexia were also diagnosed with an attention deficit hyperactivity disroder and were excluded from further analyses. Participants performed in a saccadic adaptation task in which visual errors were introduced at the end of saccadic eye movements. The amplitudes of primary saccades were measured and plotted as a function of the order in which they occurred. Lines of best fit were calculated. Significant changes in the amplitude of primary saccades were identified. |
Christine M. Gamble; Joo-Hyun Song Dynamic modulation of illusory and physical target size on separate and coordinated eye and hand movements Journal Article In: Journal of Vision, vol. 17, no. 3, pp. 1–23, 2017. @article{Gamble2017, In everyday behavior, two of the most common visually guided actions-eye and hand movements-can be performed independently, but are often synergistically coupled. In this study, we examine whether the same visual representation is used for different stages of saccades and pointing, namely movement preparation and execution, and whether this usage is consistent between independent and naturalistic coordinated eye and hand movements. To address these questions, we used the Ponzo illusion to dissociate the perceived and physical sizes of visual targets and measured the effects on movement preparation and execution for independent and coordinated saccades and pointing. During independent movements, we demonstrated that both physically and perceptually larger targets produced faster preparation for both effectors. Furthermore, participants who showed a greater influence of the illusion on saccade preparation also showed a greater influence on pointing preparation, suggesting that a shared mechanism involved in preparation across effectors is influenced by illusions. However, only physical but not perceptual target sizes influenced saccade and pointing execution. When pointing was coordinated with saccades, we observed different dynamics: pointing no longer showed modulation from illusory size, while saccades showed illusion modulation for both preparation and execution. Interestingly, in independent and coordinated movements, the illusion modulated saccade preparation more than pointing preparation, with this effect more pronounced during coordination. These results suggest a shared mechanism, dominated by the eyes, may underlie visually guided action preparation across effectors. Furthermore, the influence of illusions on action may operate within such a mechanism, leading to dynamic interactions between action modalities based on task demands. |
Ying Gao; Bernhard A. Sabel Microsaccade dysfunction and adaptation in hemianopia after stroke Journal Article In: Restorative Neurology and Neuroscience, vol. 35, no. 4, pp. 365–376, 2017. @article{Gao2017, Background: Besides the reduction of visual field size, hemianopic patients may also experience other poorly understood symptoms such as blurred vision, diplopia, or reduced visual acuity, which may be related to microsaccade function. Objective: To determine (i) if microsaccades are altered in hemianopia; (ii) how altered microsaccade features correlate with visual performances; and (iii) how their direction relates to visual field defect topography. Methods: In this case-control study, microsaccades ofhemianopic stroke patients (n = 14) were assessed with high-resolution eye-tracking technique, compared with those of healthy controls (n = 14), and correlated with visual performances, visual field defect parameters and lesion age. Results: Patients' microsaccades had (i) larger amplitude (P= 0.027), (ii) longer duration (P= 0.042), and (iii) impaired binocular microsaccade conjugacy (horizontal: P= 0.002; vertical: P= 0.035). Older lesions were associated with poorer binocular conjugacy (horizontal: r(14) = 0.67 |
Hayward J. Godwin; Erik D. Reichle; Tamaryn Menneer Modeling lag-2 revisits to understand trade-offs in mixed control of fixation termination during visual search Journal Article In: Cognitive Science, vol. 41, no. 4, pp. 996–1019, 2017. @article{Godwin2017a, An important question about eye-movement behavior is when the decision is made to terminate a fixation and program the following saccade. Different approaches have found converging evidence in favor of a mixed-control account, in which there is some overlap between processing information at fixation and planning the following saccade. We examined one interesting instance of mixed control in visual search: lag-2 revisits, during which observers fixate a stimulus, move to a different stimulus, and then revisit the first stimulus on the next fixation. Results show that the probability of lag-2 revisits occurring increased with the number of target-similar stimuli, and revisits were preceded by a brief fixation on the intervening distractor stimulus. We developed the Efficient Visual Sampling (EVS) computational model to simulate our findings (fixation durations and fixation locations) and to provide insight into mixed control of fixations and the perceptual, cognitive, and motor processes that produce lag-2 revisits. |
Tal Golan; Ido Davidesco; Meir Meshulam; David M. Groppe; Pierre Mégevand; Erin M. Yeagle; Matthew S. Goldfinger; Michal Harel; Lucia Melloni; Charles E. Schroeder; Leon Y. Deouell; Ashesh D. Mehta; Rafael Malach Increasing suppression of saccade-related transients along the human visual hierarchy Journal Article In: eLife, vol. 6, pp. 1–15, 2017. @article{Golan2017, A key hallmark of visual perceptual awareness is robustness to instabilities arising from unnoticeable eye and eyelid movements. In previous human intracranial (iEEG) work (Golan et al., 2016) we found that excitatory broadband high-frequency activity transients, driven by eye blinks, are suppressed in higher-level but not early visual cortex. Here, we utilized the broad anatomical coverage of iEEG recordings in 12 eye-tracked neurosurgical patients to test whether a similar stabilizing mechanism operates following small saccades. We compared saccades (1.3°-3.7°) initiated during inspection of large individual visual objects with similarly-sized external stimulus displacements. Early visual cortex sites responded with positive transients to both conditions. In contrast, in both dorsal and ventral higher-level sites the response to saccades (but not to external displacements) was suppressed. These findings indicate that early visual cortex is highly unstable compared to higher-level visual regions which apparently constitute the main target of stabilizing extra-retinal oculomotor influences. |
Martin Gorges; Melanie N. Maier; Johannes Rosskopf; Olga Vintonyak; Elmar H. Pinkhardt; Albert C. Ludolph; Hans Peter Müller; Jan Kassubek In: Journal of Neurology, vol. 264, no. 9, pp. 1919–1928, 2017. @article{Gorges2017, Characteristic alterations of eye movement control are a common feature of neurodegenerative parkinsonism, including Parkinson's disease (PD), progressive supranuclear palsy (PSP), and multiple system atrophy (MSA). Regional microstructural alterations as assessed by diffusion tensor imaging (DTI) have been reported in PD, PSP, and MSA. Therefore, we investigated the specific association between eye movement disturbances and microstructural impairment in these diseases. Video-oculographic recordings of smooth pursuit and visually guided reactive saccades as well as fractional anisotropy (FA) maps computed from whole-brain DTI data were analyzed for 36 PD, 30 PSP, 18 MSA patients, and 23 matched healthy control subjects. In PSP, peak eye velocity was pathologically slowed compared to controls (p < 0.001) and correlated significantly with microstructural impairment in the midbrain (p < 0.001, corrected). Smooth pursuit eye movements were substantially disturbed in MSA mainly by characteristic 'catch-up' saccades resulting in significantly reduced pursuit gain (p < 0.001, corrected), and the shape of saccadized pursuit in MSA was significantly correlated with FA reductions in the middle cerebral peduncle (p < 0.001, FDR corrected). The prevalence of saccadic intrusions as a measure for inhibitory control was significantly increased in PD compared with controls (p < 0.001), but was uncorrelated with FA in cortical and subcortical white matter. Eye movement disturbances in PSP and MSA-but not in PD-are associated with diagnosis-specific regional microstructural alterations in the white matter. The non-invasive quantified oculomotor function analysis can give clues to the underlying structural connectivity network pathology and underpins its role as a technical marker in PSP and MSA. |
Frédéric Gosselin; Simon Faghel-Soubeyrand Stationary objects flashed periodically appear to move during smooth pursuit eye movement Journal Article In: Perception, vol. 46, no. 7, pp. 874–881, 2017. @article{Gosselin2017, We discovered that a white disc flashed twice at the same location appears to move during smooth pursuit eye tracking in the direction opposite to that of the eye movement. We called this novel phenomenon movement-induced apparent motion (MIAM). Using the method of constant stimuli, we measured the required displacement of the second appearance of the disc in the pursuit direction to null the effect during the closed-loop stage of smooth pursuit eye tracking. We observed a strong linear relationship between the points of subjective stationarity and the inter-stimuli intervals for four smooth pursuit eye movement speeds. The slopes and y-intercepts of these linear fits were well predicted by the hypothesis according to which subjects saw illusory motion from the first to the second retinal projections of the flashed disc during smooth pursuit eye movement, with no extra-retinal signal compensation. |
John A. Greenwood; Martin Szinte; Bilge Sayim; Patrick Cavanagh Variations in crowding, saccadic precision, and spatial localization reveal the shared topology of spatial vision Journal Article In: Proceedings of the National Academy of Sciences, vol. 114, no. 17, pp. E3573–E3582, 2017. @article{Greenwood2017, Visual sensitivity varies across the visual field in several characteristic ways. For example, sensitivity declines sharply in peripheral (vs. foveal) vision and is typically worse in the upper (vs. lower) visual field. These variations can affect processes ranging from acuity and crowding (the deleterious effect of clutter on object recognition) to the precision of saccadic eye movements. Here we examine whether these variations can be attributed to a common source within the visual system. We first compared the size of crowding zones with the precision of saccades using an oriented clock target and two adjacent flanker elements. We report that both saccade precision and crowded-target reports vary idiosyncratically across the visual field with a strong correlation across tasks for all participants. Nevertheless, both group-level and trial-by-trial analyses reveal dissociations that exclude a common representation for the two processes. We therefore compared crowding with two measures of spatial localization: Landolt-C gap resolution and three-dot bisection. Here we observe similar idiosyncratic variations with strong interparticipant correlations across tasks despite considerably finer precision. Hierarchical regression analyses further show that variations in spatial precision account for much of the variation in crowding, including the correlation between crowding and saccades. Altogether, we demonstrate that crowding, spatial localization, and saccadic precision show clear dissociations, indicative of independent spatial representations, whilst nonetheless sharing idiosyncratic variations in spatial topology. We propose that these topological idiosyncrasies are established early in the visual system and inherited throughout later stages to affect a range of higher-level representations. |
Svenja Gremmler; Markus Lappe Saccadic suppression during voluntary versus reactive saccades Journal Article In: Journal of Vision, vol. 17, no. 8, pp. 1–10, 2017. @article{Gremmler2017, Saccades are fast eye movements that reorient gaze. They can be performed voluntarily-for example, when viewing a scene-but they can also be triggered in reaction to suddenly appearing targets. The generation of these voluntary and reactive saccades have been shown to involve partially different cortical pathways. However, saccades of either type confront the visual system with a major challenge from massive image motion on the retina. Despite the fact that the whole scene is swept across the retina, a saccade usually does not elicit a percept of motion. This saccadic omission has been linked to a transient decrease of visual sensitivity during the eye movement, a phenomenon called saccadic suppression. A passive origin of saccadic suppression based on temporal masking has been proposed as well as an active central process that inhibits visual processing during the saccade. The latter one would need to include an extraretinal signal, which is generated already during saccade preparation. Since saccade generation differs for voluntary and reactive saccades, timing and nature of this extraretinal signal as well as its impact on visual sensitivity might also differ. We measured detection thresholds for luminance stimuli that were flashed during voluntary and reactive saccades and during fixation. Detection thresholds were higher during voluntary than during reactive saccades such that suppression appeared stronger during voluntary saccades. Stronger suppression in voluntary saccades could arise from a stronger extraretinal signal that activates suppression or could indicate that a suppression underlying process itself partially differs between voluntary and reactive saccades. |
Yanping Liu; Ren Huang; Dingguo Gao; Erik D. Reichle Further tests of a dynamic-adjustment account of saccade targeting during the reading of Chinese Journal Article In: Cognitive Science, vol. 41, pp. 1264–1287, 2017. @article{Liu2017a, There are two accounts of how readers of unspaced writing systems (e.g., Chinese) know where to move their eyes: (a) saccades are directed toward default targets (e.g., centers of words that have been segmented in the parafovea); or (b) saccade lengths are adjusted dynamically, as a function of ongoing parafoveal processing. This article reports an eye-movement experiment supporting the latter hypothesis by demonstrating that the slope of the relationship between the saccade launch site on word "N" and the subsequent fixation landing site on word "N" + 1 is > 1, suggesting that saccades are lengthened from launch sites that afford more parafoveal processing. This conclusion is then evaluated and confirmed via simulations using implementations of both hypotheses (Liu, Reichle, & Li, 2016), with a discussion of these results for our understanding of saccadic targeting during reading and existing models of eye-movement control. |
Yanping Liu; Ren Huang; Yugang Li; Dingguo Gao The word frequency effect on saccade targeting during Chinese reading: Evidence from a survival analysis of saccade length Journal Article In: Frontiers in Psychology, vol. 8, pp. 116, 2017. @article{Liu2017b, Our study employs distributional analysis (i.e., survival analysis) to examine how the frequency of target words influences saccade lengths into and out of these target words in Chinese reading. The results of survival analysis indicate the survival curves in the high- and low-frequency conditions diverge for a short saccade length, with more than 80% of the lengths of incoming and outgoing saccades being larger than the divergence points. These results as well as simulations using the novel Dynamic-adjustment Model of saccadic targeting (Liu et al., 2016) are consistent with previous mean-based results and provide more precise information to support this novel model. The implications for saccade target selection during the reading of Chinese are discussed. |
Zheng Ma; Scott N. J. Watamaniuk; Stephen J. Heinen Illusory motion reveals velocity matching, not foveation, drives smooth pursuit of large objects Journal Article In: Journal of Vision, vol. 17, no. 12, pp. 1–14, 2017. @article{Ma2017b, When small objects move in a scene, we keep them foveated with smooth pursuit eye movements. Although large objects such as people and animals are common, it is nonetheless unknown how we pursue them since they cannot be foveated. It might be that the brain calculates an object's centroid, and then centers the eyes on it during pursuit as a foveation mechanism might. Alternatively, the brain merely matches the velocity by motion integration. We test these alternatives with an illusory motion stimulus that translates at a speed different from its retinal motion. The stimulus was a Gabor array that translated at a fixed velocity, with component Gabors that drifted with motion consistent or inconsistent with the translation. Velocity matching predicts different pursuit behaviors across drift conditions, while centroid matching predicts no difference. We also tested whether pursuit can segregate and ignore irrelevant local drifts when motion and centroid information are consistent by surrounding the Gabors with solid frames. Finally, observers judged the global translational speed of the Gabors to determine whether smooth pursuit and motion perception share mechanisms. We found that consistent Gabor motion enhanced pursuit gain while inconsistent, opposite motion diminished it, drawing the eyes away from the center of the stimulus and supporting a motion-based pursuit drive. Catch-up saccades tended to counter the position offset, directing the eyes opposite to the deviation caused by the pursuit gain change. Surrounding the Gabors with visible frames canceled both the gain increase and the compensatory saccades. Perceived speed was modulated analogous to pursuit gain. The results suggest that smooth pursuit of large stimuli depends on the magnitude of integrated retinal motion information, not its retinal location, and that the position system might be unnecessary for generating smooth velocity to large pursuit targets. |
Jun Maruta; Peter Modera; Umesh Rajashekar; Lisa A. Spielman; Jamshid Ghajar Frequency responses to visual tracking stimuli may be affected by concussion Journal Article In: Military Medicine, vol. 182, no. 3-4, pp. 120–123, 2017. @article{Maruta2017a, Human visual tracking performance is known to be reduced with an increase of the target's speed and oscillation frequency, but changes in brain states following a concussion may alter these frequency responses. The goal of this study was to characterize and compare frequency-dependent smooth pursuit velocity degradation in normal subjects and patients who had chronic postconcussion symptoms, and also examine cases of acutely concussed patients. Eye movements were recorded while subjects tracked a target that moved along a circular trajectory of 10° radius at 0.33, 0.40, or 0.67 Hz. Performance was characterized by the gain of smooth pursuit velocity, with reduced gain indicating reduced performance. The difference between normal and chronic patient groups in the pattern of decrease in the gain of horizontal smooth pursuit velocity as a function of the stimulus frequency reflected patients performing more poorly than normal subjects at 0.4 Hzwhile both groups performing similarly at 0.33 or 0.67 Hz. The performance of acute patients may represent yet another type of frequency response. The findings suggest that there may be ranges of stimulus frequencies that differentiate the effects of concussion from normal individuals. |
Jun Maruta; Lisa A. Spielman; Umesh Rajashekar; Jamshid Ghajar Visual tracking in development and aging Journal Article In: Frontiers in Neurology, vol. 8, pp. 640, 2017. @article{Maruta2017, A moving target is visually tracked with a combination of smooth pursuit and saccades. Human visual tracking eye movement develops through early childhood and adolescence, and declines in senescence. However, the knowledge regarding performance changes over the life course is based on data from distinct age groups in isolation using different procedures, and thus is fragmented. We sought to describe the age-dependence of visual tracking performance across a wide age range and compare it to that of simple visuo-manual reaction time. We studied a cross-sectional sample of 143 subjects aged 7-82 years old (37% male). Eye movements were recorded using video-oculography, while subjects viewed a computer screen and tracked a small target moving along a circular trajectory at a constant speed. For simple reaction time (SRT) measures, series of key presses that subjects made in reaction to cue presentation on a computer monitor were recorded using a standard software. The positional precision and smooth pursuit velocity gain of visual tracking followed a U-shaped trend over age, with best performances achieved between the ages of 20 and 50 years old. A U-shaped trend was also found for mean reaction time in agreement with the existing literature. Inter-individual variability was evident at any age in both visual tracking and reaction time metrics. Despite the similarity in the overall developmental and aging trend, correlations were not found between visual tracking and reaction time performances after subtracting the effects of age. Furthermore, while a statistically significant difference between the sexes was found for mean SRT in the sample, a similar difference was not found for any of the visual tracking metrics. Therefore, the cognitive constructs and their neural substrates supporting visual tracking and reaction time performances appear largely independent. In summary, age is an important covariate for visual tracking performance, especially for a pediatric population. Since visual tracking performance metrics may provide signatures of abnormal neurological or cognitive states independent of reaction time-based metrics, further understanding of age-dependent variations in normal visual tracking behavior is necessary. |
Nicolas Masson; Mauro Pesenti; Valérie Dormal Impact of optokinetic stimulation on mental arithmetic Journal Article In: Psychological Research, vol. 81, no. 4, pp. 840–849, 2017. @article{Masson2017, Solving arithmetic problems has been shown to induce shifts of spatial attention, subtraction problems orienting attention to the left side, and addition problems to the right side of space. At the neurofunctional level, the activations elicited by the solving of arithmetical problems resemble those elicited by horizontal eye movements. Whether overt orientation of attention (i.e., eye movements) can be linked to the solving procedure is, however, still under debate. In the present study, we used optokinetic stimulation (OKS) to trigger automatic eye movements to orient participants' overt attention to the right or to the left of their visual field while they were solving addition or subtraction problems. The results show that, in comparison to leftward OKS and a control condition, rightward OKS facilitates the solving of addition problems that necessitate a carrying procedure. Subtraction solving was unaffected by leftward or rightward OKS. These results converge with previous findings to show that attentional shifts are functionally related to mental arithmetic processing |
James Mathew; Alexandre Eusebio; Frederic R. Danion Limited contribution of primary motor cortex in eye-hand coordination: A TMS study Journal Article In: Journal of Neuroscience, vol. 37, no. 40, pp. 9730 –9740, 2017. @article{Mathew2017, The ability to track a moving target with the eye is substantially improved when the target is self-moved compared with when it is moved by an external agent. To account for this observation, it has been postulated that the oculomotor system has access to hand efference copy, thereby allowing to predict the motion of the visual target. Along this scheme, we tested the effect of transcranial magnetic stimulation (TMS) over the hand area of the primary motor cortex (M1) when human participants (50% females) are asked to track with their eyes a visual target whose horizontal motion is driven by their grip force. We reasoned that, if the output of M1 is used by the oculomotor system to keep track of the target, on top of inducing short latency disturbance of grip force, single-pulse TMS should also quickly disrupt ongoing eye motion. For comparison purposes, the effect of TMS over M1 was monitored when subjects tracked an externally moved target (while keeping their hand at rest or not). In both cases, results showed no alterations in smooth pursuit, meaning that its velocity was unaffected within the 25-125 ms epoch that followed TMS. Overall, our results imply that the output of M1 has limited contribution in driving the eye motion during our eye-hand coordination task. This study suggests that, if hand motor signals are accessed by the oculomotor system, this is upstream of M1. |
Annegret Meermeier; Svenja Gremmler; Markus Lappe New is always better: Novelty modulates oculomotor learning Journal Article In: Journal of Vision, vol. 17, no. 11, pp. 1–7, 2017. @article{Meermeier2017, Saccadic adaptation aims at keeping saccades accurate to enable precise foveation of objects. It has been believed to be a rather low-level adjustment, responding chiefly to direction and magnitude of postsaccadic position error. However, recent studies have shown that image content can modify saccadic adaptation. Adaptation is more complete for saccades toward socially relevant human figures in comparison to noise when time constraints exist. In the present experiment, we show that saccadic adaptation is also susceptible to the novelty of a stimulus. In a scanning adaptation paradigm, 20 subjects participated in two sessions of forward adaptation to one position at which the same human picture was always displayed versus a position at which a new human figure was presented in every trial. Saccadic adaptation was more complete to the novel-target position. This suggests that novelty can increase oculomotor learning and corroborates the claim that saccadic adaptation includes influences that reflect the target's visual properties. |
Annegret Meermeier; Svenja Gremmler; Kerstin Richert; Til Eckermann; Markus Lappe The reward of seeing: Different types of visual reward and their ability to modify oculomotor learning Journal Article In: Journal of Vision, vol. 17, no. 12, pp. 1–13, 2017. @article{Meermeier2017a, Saccadic adaptation is an oculomotor learning process that maintains the accuracy of eye movements to ensure effective perception of the environment. Although saccadic adaptation is commonly considered an automatic and low-level motor calibration in the cerebellum, we recently found that strength of adaptation is influenced by the visual content of the target: pictures of humans produced stronger adaptation than noise stimuli. This suggests that meaningful images may be considered rewarding or valuable in oculomotor learning. Here we report three experiments that establish the boundaries of this effect. In the first, we tested whether stimuli that were associated with high and low value following long term self-administered reinforcement learning produce stronger adaptation. Twenty-eight expert gamers participated in two sessions of adaptation to game-related high-and low-reward stimuli, but revealed no difference in saccadic adaptation (Bayes Factor 01 ¼ 5.49). In the second experiment, we tested whether cognitive (literate) meaning could induce stronger adaptation by comparing targets consisting of words and nonwords. The results of twenty subjects revealed no difference in adaptation strength (Bayes Factor 01 ¼ 3.21). The third experiment compared images of human figures to noise patterns for reactive saccades. Twenty-two subjects adapted significantly more toward images of human figures in comparison to noise (p , 0.001). We conclude that only primary (human vs. noise), but not secondary, reinforcement affects saccadic adaptation (words vs. nonwords, high-vs. low-value video game images). |
Geoffrey Megardon; Casimir J. H. Ludwig; Petroc Sumner Trajectory curvature in saccade sequences: Spatiotopic influences vs. residual motor activity Journal Article In: Journal of Neurophysiology, vol. 118, no. 2, pp. 1310–1320, 2017. @article{Megardon2017, When decisions drive saccadic eye movements, traces of the decision process can be inferred from the movement trajectories. For example, saccades can curve away from distractor stimuli, which was thought to reflect cortical inhibition biasing activity in the superior colliculus. Recent neurophysiological work does not support this theory, and two recent models have replaced top-down inhibition with lateral interactions in the superior colliculus or neural fatigue in the brainstem saccadic burst generator. All current models operate in retinotopic coordinates and are based on single saccade paradigms. To extend these models to sequences of saccades, we assessed whether and how saccade curvature depends on previously fixated locations and the direction of previous saccades. With a two-saccade paradigm, we first demonstrated that second saccades curved away from the initial fixation stimulus. Furthermore, by varying the time from fixation offset and the intersaccadic duration, we distinguished the extent of curvature originating from the spatiotopic representation of the previous fixation location or residual motor activity of the previous saccade. Results suggest that both factors drive curvature, and we discuss how these effects could be implemented in current models. In particular, we propose that the collicular retinotopic maps receive an excitatory spatiotopic update from the lateral interparial region. |
Dimitrios J. Palidis; Pearson A. Wyder-Hodge; Jolande Fooken; Miriam Spering Distinct eye movement patterns enhance dynamic visual acuity Journal Article In: PLoS ONE, vol. 12, no. 2, pp. e0172061, 2017. @article{Palidis2017, Dynamic visual acuity (DVA) is the ability to resolve fine spatial detail in dynamic objects during head fixation, or in static objects during head or body rotation. This ability is important for many activities such as ball sports, and a close relation has been shown between DVA and sports expertise. DVA tasks involve eye movements, yet, it is unclear which aspects of eye movements contribute to successful performance. Here we examined the relation between DVA and the kinematics of smooth pursuit and saccadic eye movements in a cohort of 23 varsity baseball players. In a computerized dynamic-object DVA test, observers reported the location of the gap in a small Landolt-C ring moving at various speeds while eye movements were recorded. Smooth pursuit kinematics—eye latency, acceleration, velocity gain, position error—and the direction and amplitude of saccadic eye movements were linked to perceptual performance. Results reveal that distinct eye movement patterns—minimizing eye position error, tracking smoothly, and inhibiting reverse saccades—were related to dynamic visual acuity. The close link between eye movement quality and DVA performance has important implications for the development of perceptual training programs to improve DVA. |
Maria Panagiotidi; Paul Overton; Tom Stafford Increased microsaccade rate in individuals with ADHD rate Journal Article In: Journal of Eye Movement Research, vol. 10, no. 1, pp. 1–9, 2017. @article{Panagiotidi2017, Microsaccades are involuntary, small, jerk-like eye-movements with high-velocity that are observed during fixation. Abnormal microsaccade rates and characteristics have been ob- served in a number of psychiatric and developmental disorders. In this study, we examine microsaccade differences in 43 non-clinical participants with high and low levels of ADHD- like traits, assessed with the Adult ADHD Self-Report Scale (ASRS, Kessler, Adler, et al., 2005). A simple sustained attention paradigm, which has been previously shown to elicit microsaccades, was employed. A positive correlation was found between ADHD-like traits and microsaccade rates. No other differences in microsaccade properties were observed. The relationship between ADHD traits and microsaccades suggests that oculomotor behaviour could potentially lead to the development of a biomarker for the ADHD. |
2016 |
Jolande Fooken; Sang-Hoon Yeo; Dinesh K. Pai; Miriam Spering Eye movement accuracy determines natural interception strategies Journal Article In: Journal of Vision, vol. 16, no. 14, pp. 1–15, 2016. @article{Fooken2016, Eye movements aid visual perception and guide actions such as reaching or grasping. Most previous work on eye-hand coordination has focused on saccadic eye movements. Here we show that smooth pursuit eye movement accuracy strongly predicts both interception accuracy and the strategy used to intercept a moving object. We developed a naturalistic task in which participants (n = 42 varsity baseball players) intercepted a moving dot (a "2D fly ball") with their index finger in a designated "hit zone." Participants were instructed to track the ball with their eyes, but were only shown its initial launch (100-300 ms). Better smooth pursuit resulted in more accurate interceptions and determined the strategy used for interception, i.e., whether interception was early or late in the hit zone. Even though early and late interceptors showed equally accurate interceptions, they may have relied on distinct tactics: early interceptors used cognitive heuristics, whereas late interceptors' performance was best predicted by pursuit accuracy. Late interception may be beneficial in real-world tasks as it provides more time for decision and adjustment. Supporting this view, baseball players who were more senior were more likely to be late interceptors. Our findings suggest that interception strategies are optimally adapted to the proficiency of the pursuit system |
K. B. Pedersen; A. K. Sjølie; A. H. Vestergaard; S. Andréasson; F. Møller In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 254, no. 10, pp. 1897–1908, 2016. @article{Pedersen2016, Purpose: To quantify fixation stability in patients with neovascular age-related macular degeneration (nAMD) at baseline, 3 and 6 months after anti-vascular endothelial growth factor (anti-VEGF) treatment and furthermore asses the implications ofan unsteady fixation for multifocal electroretinography (mfERG) measurements. Methods: Fifty eyes of 50 nAMD patients receiving intravitreal anti-VEGF treatment with either bevacizumab or ranibizumab and eight eyes of eight control subjects were included. Fixation stability measurements were performed with the Eye-Link eyetracking system and the retinal area in degrees2 (deg2) containing the 68 % most frequently used fixation points (RAF68) was calculated. MfERG P1 amplitude and implicit time were analyzed in six concentric rings and as a summed response. Patients were examined at baseline, 3 and 6 months. Four different mfERG recordings were performed for the control subjects to mimic an involuntary unstable fixation: normal central fixation, 2.4°, 4.8°, and 7.1° fixation instability. Results: For control subjects, a fixation instability of2.4° (corresponding to the central hexagon) did not reduce mfERG ring amplitudes significantly, whereas 4.8° and 7.1° fixation instability reduced the amplitudes significantly in rings 1 and 2 (p<0.001) as well as in the peripheral rings in the 7.1° instability condition (p< 0.001). Fixation stability improved non- significantly for patients at 3 and 6 months. The size of the retinal area of fixation was at baseline, 3 and 6 months nega- tively correlated to visual acuity (VA) (rbaseline =−0.65, r3 months =−0.60, and r6 months =−0.66 respectively, p< 0.001) and mfERG amplitudes of the three innermost rings (rbaseline =−0.29 |
Stephen M. Lee; Alicia Peltsch; Maureen Kilmade; Donald C. Brien; Brian C. Coe; Ingrid S. Johnsrude; Douglas P. Munoz Neural correlates of predictive saccades Journal Article In: Journal of Cognitive Neuroscience, vol. 28, no. 8, pp. 1210–1227, 2016. @article{Lee2016, Every day we generate motor responses that are timed with external cues. This phenomenon of sensorimotor synchronization has been simplified and studied extensively using finger tapping sequences that are executed in synchrony with auditory stimuli. The predictive saccade paradigm closely resembles the finger tapping task. In this paradigm, participants follow a visual target that “steps” between two fixed locations on a visual screen at predictable ISIs. Eventually, the time from target appearance to saccade initiation (i.e., saccadic RT) becomes predictive with values nearing 0 msec. Unlike the finger tapping literature, neural control of predictive behavior described within the eye movement literature has not been well established and is inconsistent, especially between neuroimaging and patient lesion studies. To resolve these discrepancies, we used fMRI to investigate the neural correlates of predictive saccades by con- trasting brain areas involved with behavior generated from the predictive saccade task with behavior generated from a reactive saccade task (saccades are generated toward targets that are unpredictably timed). We observed striking differences in neural recruitment between reactive and predictive conditions: Reactive saccades recruited oculomotor structures, as predicted, whereas predictive saccades recruited brain structures that support tim- ing inmotor responses, such as the crus I of the cerebellum, and structures commonly associated with the default mode network. Therefore, our results were more consistent with those found in the finger tapping literature. |
Cécile Eymond; Patrick Cavanagh; Thérèse Collins Feature-based attention across saccades and immediate postsaccadic selection Journal Article In: Attention, Perception, and Psychophysics, vol. 78, no. 5, pp. 1293–1301, 2016. @article{Eymond2016, Before each eye movement, attentional resources are drawn to the saccade goal. This saccade-related attention is known to be spatial in nature, and in this study we asked whether it also evokes any feature selectivity that is maintained across the saccade. After a saccade toward a colored target, participants performed a postsaccadic feature search on an array displayed at landing. The saccade target either had the same color as the search target in the postsaccadic array (congruent trials) or a different color (incongruent or neutral trials). Our results show that the color of the saccade target did not prime the subsequent feature search. This suggests that "landmark search", the process of searching for the saccade target once the eye lands (Deubel in Visual Cognition, 11, 173-202, 2004), may not involve the attentional mechanisms that underlie feature search. We also analyzed intertrial effects and observed priming of pop-out (Maljkovic & Nakayama in Memory & Cognition, 22, 657-672, 1994) for the postsaccadic feature search: the detection of the color singleton became faster when its color was repeated on successive trials. However, search performance revealed no effect of congruency between the saccade and search targets, either within or across trials, suggesting that the priming of pop-out is specific to target repetitions within the same task and is not seen for repetitions across tasks. Our results support a dissociation between feature-based attention and the attentional mechanisms associated with eye movement programming. |
Masaki Emoto; Hideki Fukuda Correlation between peak velocity of saccades and susceptibility to motion blur Journal Article In: Journal of Display Technology, vol. 12, no. 9, pp. 976–981, 2016. @article{Emoto2016, A major problem in the subjective evaluation of TV image quality is individual variability among viewers. If observers are not carefully selected for viewing studies, large individual differences in the susceptibility to image blurring result in imprecise evaluations and loss of power to detect statistically significant differences between experimental conditions. In assessments of the picture quality of traditional television, which has a narrow field of view (FOV), observers' visual acuity (VA) should be screened before the subjective evaluations. For emerging TV systems with wide FOV (Ultra-High-Definition TV: UHDTV), in which objects move quickly relative to the display frame, it is unclear whether screening viewers' VA is sufficient for selecting viewers to subjectively evaluate moving picture quality or sharpness. Here, we evaluated saccadic eye movement parameters to identify adequate methods to screen participants for studies evaluating UHDTV motion image quality. Each participant's evaluations of two moving pictures were highly correlated, suggesting that participants evaluated sharpness consistently. A significant correlation was observed between the average subjective evaluation score and the peak saccade velocity, but not the VA, of each participant. We conclude that each participant has a certain susceptibility to image blur when evaluating moving pictures, and that this susceptibility correlates with the participant's peak saccade velocity. Thus, the objective measure of peak saccade velocity can be used to screen participants for motion picture evaluation studies. |
Ian M. Erkelens; Benjamin Thompson; William R. Bobier Unmasking the linear behaviour of slow motor adaptation to prolonged convergence Journal Article In: European Journal of Neuroscience, vol. 43, no. 12, pp. 1553–1560, 2016. @article{Erkelens2016, Adaptation to changing environmental demands is central to maintaining optimal motor system function. Current theories suggest that adaptation in both the skeletal-motor and oculomotor systems involves a combination of fast (reflexive) and slow (recalibration) mechanisms. Here we used the oculomotor vergence system as a model to investigate the mechanisms underlying slow motor adaptation. Unlike reaching with the upper limbs, vergence is less susceptible to changes in cognitive strategy that can affect the behaviour of motor adaptation. We tested the hypothesis that mechanisms of slow motor adaptation reflect early neural processing by assessing the linearity of adaptive responses over a large range of stimuli. Using varied disparity stimuli in conflict with accommodation, the slow adaptation of tonic vergence was found to exhibit a linear response whereby the rate (R(2) = 0.85, p < 0.0001) and amplitude (R(2) = 0.65, p < 0.0001) of the adaptive effects increased proportionally with stimulus amplitude. These results suggest that this slow adaptive mechanism is an early neural process, implying its fundamental physiological nature that is potentially dominated by subcortical and cerebellar substrates. |
Jasper H. Fabius; Alessio Fracasso; Stefan Van Der Stigchel Spatiotopic updating facilitates perception immediately after saccades Journal Article In: Scientific Reports, vol. 6, pp. 34488, 2016. @article{Fabius2016, As the neural representation of visual information is initially coded in retinotopic coordinates, eye movements (saccades) pose a major problem for visual stability. If no visual information were maintained across saccades, retinotopic representations would have to be rebuilt after each saccade. It is currently strongly debated what kind of information (if any at all) is accumulated across saccades, and when this information becomes available after a saccade. Here, we use a motion illusion to examine the accumulation of visual information across saccades. In this illusion, an annulus with a random texture slowly rotates, and is then replaced with a second texture (motion transient). With increasing rotation durations, observers consistently perceive the transient as large rotational jumps in the direction opposite to rotation direction (backward jumps). We first show that accumulated motion information is updated spatiotopically across saccades. Then, we show that this accumulated information is readily available after a saccade, immediately biasing postsaccadic perception. The current findings suggest that presaccadic information is used to facilitate postsaccadic perception and are in support of a forward model of transsaccadic perception, aiming at anticipating the consequences of eye movements and operating within the narrow perisaccadic time window. |
Alessio Fracasso; David Melcher Saccades influence the visibility of targets in rapid stimulus sequences: The Roles of mislocalization, retinal distance and remapping Journal Article In: Frontiers in Systems Neuroscience, vol. 10, pp. 58, 2016. @article{Fracasso2016, Briefly presented targets around the time of a saccade are mislocalized towards the saccadic landing point. This has been taken as evidence for a remapping mechanism that accompanies each eye movement, helping maintain visual stability across large retinal shifts. Previous studies have shown that spatial mislocalization is greatly diminished when trains of brief stimuli are presented at a high frequency rate, which might help to explain why mislocalization is rarely perceived in everyday viewing. Studies in the laboratory have shown that mislocalization can reduce metacontrast masking by causing target stimuli in a masking sequence to be perceived as shifted in space towards the saccadic target and thus more easily discriminated. We investigated the influence of saccades on target discrimination when target and masks were presented in a rapid serial visual presentation (RSVP), as well as with forward masking and with backward masking. In a series of experiments, we found that performance was influenced by the retinal displacement caused by the saccade itself but that an additional component of un-masking occurred even when the retinal location of target and mask was matched. These results speak in favor of a remapping mechanism that begins before the eyes start moving and continues well beyond saccadic termination. |
Josselin Gautier; Harold E. Bedell; John Siderov; Sarah J. Waugh Monocular microsaccades are visual-task related Journal Article In: Journal of Vision, vol. 16, no. 3, pp. 1–16, 2016. @article{Gautier2016, During visual fixation, we constantly move our eyes. These microscopic eye movements are composed of tremor, drift, and microsaccades. Early studies concluded that microsaccades, like larger saccades, are binocular and conjugate, as expected from Hering's law of equal innervation. Here, we document the existence of monocular microsaccades during both fixation and a discrimination task, reporting the location of the gap in a foveal, low-contrast letter C. Monocular microsaccades differ in frequency, amplitude, and peak velocity from binocular microsaccades. Our analyses show that these differences are robust to different velocity and duration criteria that have been used previously to identify microsaccades. Also, the frequency of monocular microsaccades differs systematically according to the task: monocular microsaccades occur more frequently during fixation than discrimination, the opposite of their binocular equivalents. However, during discrimination, monocular microsaccades occur more often around the discrimination threshold, particularly for each subject's dominant eye and in case of successful discrimination. We suggest that monocular microsaccades play a functional role in the production of fine corrections of eye position and vergence during demanding visual tasks. |
David C. Godlove; Jeffrey D. Schall Microsaccade production during saccade cancelation in a stop-signal task Journal Article In: Vision Research, vol. 118, pp. 5–16, 2016. @article{Godlove2016, We obtained behavioral data to evaluate two alternative hypotheses about the neural mechanisms of gaze control. The "fixation" hypothesis states that neurons in rostral superior colliculus (SC) enforce fixation of gaze. The "microsaccade" hypothesis states that neurons in rostral SC encode microsaccades rather than fixation per se. Previously reported neuronal activity in monkey SC during the saccade stop-signal task leads to specific, dissociable behavioral predictions of these two hypotheses. When subjects are required to cancel partially-prepared saccades, imbalanced activity spreads across rostral and caudal SC with a reliable temporal profile. The microsaccade hypothesis predicts that this imbalance will lead to elevated microsaccade production biased toward the target location, while the fixation hypothesis predicts reduced microsaccade production. We tested these predictions by analyzing the microsaccades produced by 4 monkeys while they voluntarily canceled partially prepared eye movements in response to explicit stop signals. Consistent with the fixation hypothesis and contradicting the microsaccade hypothesis, we found that each subject produced significantly fewer microsaccades when normal saccades were successfully canceled. The few microsaccades escaping this inhibition tended to be directed toward the target location. We additionally investigated interactions between initiating microsaccades and inhibiting normal saccades. Reaction times were longer when microsaccades immediately preceded target presentation. However, pre-target microsaccade production did not affect stop-signal reaction time or alter the probability of canceling saccades following stop signals. These findings demonstrate that imbalanced activity within SC does not necessarily produce microsaccades and add to evidence that saccade preparation and cancelation are separate processes. |
Claudia C. Gonzalez; Jac Billington; Melanie R. Burke The involvement of the fronto-parietal brain network in oculomotor sequence learning using fMRI Journal Article In: Neuropsychologia, vol. 87, pp. 1–11, 2016. @article{Gonzalez2016a, The basis of motor learning involves decomposing complete actions into a series of predictive individual components that form the whole. The present fMRI study investigated the areas of the human brain important for oculomotor short-term learning, by using a novel sequence learning paradigm that is equivalent in visual and temporal properties for both saccades and pursuit, enabling more direct comparisons between the oculomotor subsystems. In contrast with previous studies that have implemented a series of discrete ramps to observe predictive behaviour as evidence for learning, we presented a continuous sequence of interlinked components that better represents sequences of actions. We implemented both a classic univariate fMRI analysis, followed by a further multivariate pattern analysis (MVPA) within a priori regions of interest, to investigate oculomotor sequence learning in the brain and to determine whether these mechanisms overlap in pursuit and saccades as part of a higher order learning network. This study has uniquely identified an equivalent frontal-parietal network (dorsolateral prefrontal cortex, frontal eye fields and posterior parietal cortex) in both saccades and pursuit sequence learning. In addition, this is the first study to investigate oculomotor sequence learning during fMRI brain imaging, and makes significant contributions to understanding the role of the dorsal networks in motor learning. |
Svenja Gremmler; Markus Lappe Saccadic adaptation is associated with starting eye position Journal Article In: Frontiers in Human Neuroscience, vol. 10, pp. 322, 2016. @article{Gremmler2016, Saccadic adaptation is the motor learning process that keeps saccade amplitudes on target. This process is eye position specific: amplitude adaptation that is induced for a saccade at one particular location in the visual field transfers incompletely to saccades at other locations. In our current study, we investigated wether this eye position signal corresponds to the initial or to the final eye position of the saccade. Each case would have different implications on the mechanisms of adaptation. The initial eye position is not directly available, when the adaptation driving post saccadic error signal is received. On the other hand the final eye position signal is not available, when the motor command for the saccade is calculated. In six human subjects we adapted a saccade of 15 degree amplitude that started at a constant position. We then measured the transfer of adaptation to test saccades of 10 and 20 degree amplitude. In each case we compared test saccades that matched the start position of the adapted saccade to those that matched the target of the adapted saccade. We found significantly more transfer of adaptation to test saccades with the same start position than to test saccades with the same target position. The results indicate that saccadic adaptation is specific to the initial eye position. This is consistent with a previously proposed effect of gain field modulated input from areas like the frontal eye field, the lateral intraparietal area and the superior colliculus into the cerebellar adaptation circuitry. |
Jing Chen; Matteo Valsecchi; Karl R. Gegenfurtner LRP predicts smooth pursuit eye movement onset during the ocular tracking of self-generated movements Journal Article In: Journal of Neurophysiology, vol. 116, no. 1, pp. 18–29, 2016. @article{Chen2016c, Several studies indicated that human observers are very efficient at tracking self-generated hand movements with their gaze, yet it is not clear whether this is simply a byproduct of the predictability of self-generated actions or if it results from a deeper coupling of the somatomotor and oculomotor systems. In a first behavioral experiment we compared pursuit performance as observers either followed their own finger or tracked a dot whose motion was externally generated but mimicked their finger motion. We found that even when the dot motion was completely predictable both in terms of onset time and in terms of kinematics, pursuit was not identical to the one produced as the observers tracked their finger, as evidenced by increased rate of catch-up saccades and by the fact that in the initial phase of the movement gaze was lagging behind the dot, whereas it was ahead of the finger. In a second experiment we recorded EEG in the attempt to find a direct link between the finger motor preparation, indexed by the lateralized readiness potential (LRP), and the latency of smooth pursuit. After taking into account finger movement onset variability, we observed larger LRP amplitudes associated with earlier smooth pursuit onset across trials. The same held across subjects, where average LRP onset correlated with average eye latency. The evidence from both experiments concurs to indicate that a strong coupling exists between the motor systems leading to eye and finger movements and that simple top-down predictive signals are unlikely to support optimal coordination. |
Jing Chen; Matteo Valsecchi; Karl R. Gegenfurtner Role of motor execution in the ocular tracking of self-generated movements Journal Article In: Journal of Neurophysiology, vol. 116, no. 6, pp. 2586–2593, 2016. @article{Chen2016d, When human observers track the movements of their own hand with their gaze, the eyes can start moving before the finger (i.e., anticipatory smooth pursuit). The signals driving anticipation could come from motor commands during finger motor execution or from motor intention and decision processes associated with self-initiated movements. For the present study, we built a mechanical device that could move a visual target either in the same direction as the participant's hand or in the opposite direction. Gaze pursuit of the target showed stronger anticipation if it moved in the same direction as the hand compared with the opposite direction, as evidenced by decreased pursuit latency, increased positional lead of the eye relative to target, increased pursuit gain, decreased saccade rate, and decreased delay at the movement reversal. Some degree of anticipation occurred for incongruent pursuit, indicating that there is a role for higher-level movement prediction in pursuit anticipation. The fact that anticipation was larger when target and finger moved in the same direction provides evidence for a direct coupling between finger and eye motor commands. |
Kyoung Whan Choe; Randolph Blake; Sang-Hun Lee Pupil size dynamics during fixation impact the accuracy and precision of video-based gaze estimation Journal Article In: Vision Research, vol. 118, pp. 48–59, 2016. @article{Choe2016, Video-based eye tracking relies on locating pupil center to measure gaze positions. Although widely used, the technique is known to generate spurious gaze position shifts up to several degrees in visual angle because pupil centration can change without eye movement during pupil constriction or dilation. Since pupil size can fluctuate markedly from moment to moment, reflecting arousal state and cognitive processing during human behavioral and neuroimaging experiments, the pupil size artifact is prevalent and thus weakens the quality of the video-based eye tracking measurements reliant on small fixational eye movements. Moreover, the artifact may lead to erroneous conclusions if the spurious signal is taken as an actual eye movement. Here, we measured pupil size and gaze position from 23 human observers performing a fixation task and examined the relationship between these two measures. Results disclosed that the pupils contracted as fixation was prolonged, at both small (<16 s) and large (~4 min) time scales, and these pupil contractions were accompanied by systematic errors in gaze position estimation, in both the ellipse and the centroid methods of pupil tracking. When pupil size was regressed out, the accuracy and reliability of gaze position measurements were substantially improved, enabling differentiation of 0.1° difference in eye position. We confirmed the presence of systematic changes in pupil size, again at both small and large scales, and its tight relationship with gaze position estimates when observers were engaged in a demanding visual discrimination task. |
Woo Young Choi; Jayalakshmi Viswanathan; Jason J. S. Barton The temporal dynamics of the distractor in the global effect Journal Article In: Experimental Brain Research, vol. 234, no. 9, pp. 2457–2463, 2016. @article{Choi2016a, In the global effect, saccades are displaced towards a distractor if the latter is near to the target, an effect thought to reflect spatial averaging in neurons of the superior colliculus. The temporal dynamics of the global effect have not been well studied, however. We had twelve subjects perform horizontal saccades to a target in trials in which there were either no distractor or a distractor stim- ulus located 20° above or below the target. The distractor appeared either simultaneously with the target or preceded it by an interval of between 100 and 800 ms, and was either flashed for only 100 ms or remained visible until the sub- ject responded with a saccade. Both flashed and persistent distractors reduced saccadic latency if they preceded target onset, indicating that subjects could use this cue to pre- pare saccades in advance. Saccadic endpoint was displaced towards a flashed distractor only if it was simultaneous with the target. However, persistent distractors produced a global effect for both simultaneous presentation and dis- tractor–target intervals of 100 ms, but not for longer inter- vals. We conclude that the global effect requires of the dis- tractor both a recent onset and persistence of the distractor, and that distractor-related activity decays rapidly within 300 ms. |
Steven C. Dakin; Philip R. K. Turnbull Similar contrast sensitivity functions measured using psychophysics and optokinetic nystagmus Journal Article In: Scientific Reports, vol. 6, pp. 34514, 2016. @article{Dakin2016, Although the contrast sensitivity function (CSF) is a particularly useful way of characterising functional vision, its measurement relies on observers making reliable perceptual reports. Such procedures can be challenging when testing children. Here we describe a system for measuring the CSF using an automated analysis of optokinetic nystagmus (OKN); an involuntary oscillatory eye movement made in response to drifting stimuli, here spatial-frequency (SF) band-pass noise. Quantifying the strength of OKN in the stimulus direction allows us to estimate contrast sensitivity across a range of SFs. We compared the CSFs of 30 observers with normal vision measured using both OKN and perceptual report. The approaches yield near-identical CSFs (mean R = 0.95) that capture subtle intra-observer variations in visual acuity and contrast sensitivity (both R = 0.84, p < 0.0001). Trial-by-trial analysis reveals high correlation between OKN and perceptual report, a signature of a common neural mechanism for determining stimulus direction. We also observe conditions where OKN and report are significantly decorrelated as a result of a minority of observers experiencing direction-reversals that are not reflected by OKN. We conclude that there are a wide range of stimulus conditions for which OKN can provide a valid alternative means of measuring of the CSF. |
Anouk J. Brouwer; W. Pieter Medendorp; Jeroen B. J. Smeets Contributions of gaze-centered and object-centered coding in a double-step saccade task Journal Article In: Journal of Vision, vol. 16, no. 14, pp. 1–12, 2016. @article{Brouwer2016b, The position of a saccade target can be encoded in gaze-centered coordinates, that is, relative to the current gaze position, or in object-centered coordinates, that is, relative to an object in the environment. We tested the role of gaze-centered and object-centered coding in a double-step saccade task involving the Brentano version of the Müller-Lyer illusion. The two visual targets were presented either sequentially, requiring gaze-centered coding of the second saccade target, or simultaneously, thereby providing additional object-centered information about the location of the second target relative to the first. We found that the endpoint of the second saccade was affected by the illusion, irrespective of whether the targets were presented sequentially or simultaneously, suggesting that participants used a gaze-centered updating strategy. We found that variability in saccade endpoints was reduced when object-centered information was consistently available but not when its presence varied from trial to trial. Our results suggest that gaze-centered coding is dominant in the planning of sequential saccades, whereas object-centered information plays a relatively small role. |
Jelmer P. De Vries; R. Azadi; Mark R. Harwood The saccadic size-latency phenomenon explored: Proximal target size is a determining factor in the saccade latency Journal Article In: Vision Research, vol. 129, pp. 87–97, 2016. @article{DeVries2016a, Saccade latencies are known to increase for targets presented close to fixation. Recently, it was shown that not only target eccentricity, but the size of a proximal saccade target also plays a crucial role: latencies increase rapidly with increasing target size. Interestingly, these latency increases are greater than those typically found for other supra-threshold manipulations of target properties. Here we evaluate to what extent this phenomenon is distinct from known delays in saccade initiation and whether the phenomenon is truly related to the size of a proximal target. In Experiment 1 we focus on the importance of the required amplitude. Employing a saccade adaptation paradigm we find that the required amplitude is not a determining factor. Focusing on the role of size, in Experiment 2, we find that while latency increases are strongest for targets elongated in the direction of the fovea, elongations perpendicular to this direction also lead to an increase in latencies. Finally, in Experiment 3 we verify that the latency increases are driven by the properties of the saccade target rather than visual input in general. Together these experiments provide converging evidence that the current phenomenon is both novel and a consequence of the relation between proximal target size and its eccentricity. |
Adele Diederich; Hans Colonius; Farid I. Kandil Prior knowledge of spatiotemporal configuration facilitates crossmodal saccadic response: A TWIN analysis Journal Article In: Experimental Brain Research, vol. 234, no. 7, pp. 2059–2076, 2016. @article{Diederich2016, Saccadic reaction times from a focused-attention task with a visual target and an acoustic nontarget support the hypothesis that the amount of saccadic facilitation in the presence of a nontarget increases with the prior knowledge of alignment with the target across different blocks of trials. The time-window-of-integration model can account for the size of the effect by having window size depend on the prior knowledge of alignment. Some efforts to identify the neural correlates of the effect are discussed. |
Marianne Duyck; Thérèse Collins; Mark Wexler Masking the saccadic smear Journal Article In: Journal of Vision, vol. 16, no. 10, pp. 1–13, 2016. @article{Duyck2016, Static visual stimuli are smeared across the retina during saccades, but in normal conditions this smear is not perceived. Instead, we perceive the visual scene as static and sharp. However, retinal smear is perceived if stimuli are shown only intrasaccadically, but not if the stimulus is additionally shown before a saccade begins, or after the saccade ends (Campbell & Wurtz, 1978). This inhibition has been compared to forward and backward metacontrast masking, but with spatial relations between stimulus and mask that are different from ordinary metacontrast during fixation. Previous studies of smear masking have used subjective measures of smear perception. Here we develop a new, objective technique for measuring smear masking, based on the spatial localization of a gap in the smear created by very quickly blanking the stimulus at various points during the saccade. We apply this technique to show that smear masking survives dichoptic presentation (suggesting that it is therefore cortical in origin), as well as separations of as much as 6° between smear and mask. |
Muriel Dysli; Mathias Abegg Gaze-dependent phoria and vergence adaptation Journal Article In: Journal of Vision, vol. 16, no. 3, pp. 1–12, 2016. @article{Dysli2016a, Incomitance is a condition with gaze-dependent deviations of ocular alignment and is common in strabismus patients. The physiological mechanisms that maintain equal horizontal ocular alignment in all gaze directions (concomitance) in healthy individuals are poorly explored. We investigate adaptive processes in the vergence system that are induced by horizontal incomitant vergence stimuli (stimuli that require a gaze- dependent vergence response in order to re-establish binocular single vision). We measured horizontal vergence responses elicited after healthy subjects shifted their gaze from a position that required no vergence to a position that required convergence. Repetitive saccades into a position with a convergence stimulus rapidly decreased phoria (defined as the deviation of ocular alignment in the absence of a binocular stimulus). This change of phoria was present in all viewing directions (from 08 to 0.8686 0.408, p , 0.001) but was more pronounced in the gaze direction with a convergence stimulus (from 0.2686 0.138 to 1.3986 0.338, p , 0.001). We also found that vergence velocity rapidly increased (p ¼ 0.015) and vergence latency promptly decreased (p , 0.001). We found gaze-dependent modulation of phoria in combined saccade–vergence eye movements and also in pursuit–vergence eye movements. Thus, acute horizontal, gaze-dependent changes of vergence, such as may be encountered in new onset strabismus due to paralysis, can rapidly increase vergence velocity and decrease latency. Gaze- specific (concomitant) and gaze-independent (incomitant) phoria levels will adapt. These early adaptive processes increase the efficacy of binocular vision and maintain good ocular alignment in all directions of gaze. |
Caroline Ego; Lucie Bonhomme; Jean-Jacques Orban de Xivry; David Da Fonseca; Philippe Lefèvre; Guillaume S. Masson; Christine Deruelle Behavioral characterization of prediction and internal models in adolescents with autistic spectrum disorders Journal Article In: Neuropsychologia, vol. 91, pp. 335–345, 2016. @article{Ego2016, Autism has been considered as a deficit in prediction of the upcoming event or of the sensory consequences of our own movements. To test this hypothesis, we recorded eye movements from high-functioning autistic adolescents and from age-matched controls during a blanking paradigm. In this paradigm, adolescents were instructed to follow a moving target with their eyes even during its transient disappearance. Given the absence of visual information during the blanking period, eye movements during this period are solely controlled on the basis of the prediction of the ongoing target motion. Typical markers of predictive eye movements such as the number and accuracy of predictive saccades and the predictive reacceleration before target reappearance were identical in the two populations. In addition, the synergy of predictive saccades and smooth pursuit observed during the blanking periods, which is a marker for the quality of internal models about target/eye motions, was comparable between these two populations. These results suggest that, in our large population of high-functioning autistic adolescent, both predictive abilities and internal models are left intact in Autism, at least for low-level sensorimotor transformations. |
Caroline Ego; Demet Yüksel; Jean-Jacques Orban de Xivry; Philippe Lefèvre Development of internal models and predictive abilities for visual tracking during childhood Journal Article In: Journal of Neurophysiology, vol. 115, no. 1, pp. 301–309, 2016. @article{Ego2016a, The prediction of the consequences of our own actions through internal models is an essential component of motor control. Previous studies showed improvement of anticipatory behaviors with age for grasping, drawing, and postural control. Since these actions require visual and proprioceptive feedback, these improvements might reflect both the development of internal models and the feedback control. In contrast, visual tracking of a temporarily invisible target gives specific markers of prediction and internal models for eye movements. Therefore, we recorded eye movements in 50 children (aged 5-19 yr) and in 10 adults, who were asked to pursue a visual target that is temporarily blanked. Results show that the youngest children (5-7 yr) have a general oculomotor behavior in this task, qualitatively similar to the one observed in adults. However, the overall performance of older subjects in terms of accuracy at target reappearance and variability in their behavior was much better than the youngest children. This late maturation of predictive mechanisms with age was reflected into the development of the accuracy of the internal models governing the synergy between the saccadic and pursuit systems with age. Altogether, we hypothesize that the maturation of the interaction between smooth pursuit and saccades that relies on internal models of the eye and target displacement is related to the continuous maturation of the cerebellum. |
Alexandra S. Mueller; Esther G. González; Chris McNorgan; Martin J. Steinbach; Brian Timney Effects of vertical direction and aperture size on the perception of visual acceleration Journal Article In: Perception, vol. 45, no. 6, pp. 670–683, 2016. @article{Mueller2016a, It is not well understood whether the distance over which moving stimuli are visible affects our sensitivity to the presence of acceleration or our ability to track such stimuli. It is also uncertain whether our experience with gravity creates anisotropies in how we detect vertical acceleration and deceleration. To address these questions, we varied the vertical extent of the aperture through which we presented vertically accelerating and decelerating random dot arrays. We hypothesized that observers would better detect and pursue accelerating and decelerating stimuli that extend over larger than smaller distances. In Experiment 1, we tested the effects of vertical direction and aperture size on acceleration and deceleration detection accuracy. Results indicated that detection is better for downward motion and for large apertures, but there is no difference between vertical acceleration and deceleration detection. A control experiment revealed that our manipulation of vertical aperture size affects the ability to track vertical motion. Smooth pursuit is better (i.e., with higher peak velocities) for large apertures than for small apertures. Our findings suggest that the ability to detect vertical acceleration and deceleration varies as a function of the direction and vertical over which an observer can track the moving stimulus. |
Manon Mulckhuyse; Edwin S. Dalmaijer Distracted by danger: Temporal and spatial dynamics of visual selection in the presence of threat Journal Article In: Cognitive, Affective and Behavioral Neuroscience, vol. 16, no. 2, pp. 315–324, 2016. @article{Mulckhuyse2016, Threatening stimuli are known to influence attentional and visual processes in order to prioritize selection. For example, previous research showed faster detection of threatening relative to nonthreatening stimuli. This has led to the proposal that threatening stimuli are prioritized automatically via a rapid subcortical route. However, in most studies, the threatening stimulus is always to some extent task relevant. Therefore, it is still unclear if threatening stimuli are automatically prioritized by the visual system. We used the additional singleton paradigm with task-irrelevant fear-conditioned distractors (CS+ and CS-) and indexed the time course of eye movement behavior. The results demonstrate automatic prioritization of threat. First, mean latency of saccades directed to the neutral target was increased in the presence of a threatening (CS+) relative to a nonthreatening distractor (CS-), indicating exogenous attentional capture and delayed disengagement of covert attention. Second, more error saccades were directed to the threatening than to the nonthreatening distractor, indicating a modulation of automatically driven saccades. Nevertheless, cumulative distributions of the saccade latencies showed no modulation of threat for the fastest goal-driven saccades, and threat did not affect the latency of the error saccades to the distractors. Together these results suggest that threatening stimuli are automatically prioritized in attentional and visual selection but not via faster processing. Rather, we suggest that prioritization results from an enhanced representation of the threatening stimulus in the oculomotor system, which drives attentional and visual selection. The current findings are interpreted in terms of a neurobiological model of saccade programming. |
Antje Nuthmann; Françoise Vitu; Ralf Engbert; Reinhold Kliegl No evidence for a saccadic range effect for visually guided and memory-guided saccades in simple saccade-targeting tasks Journal Article In: PLoS ONE, vol. 11, no. 9, pp. e0162449, 2016. @article{Nuthmann2016a, Saccades to single targets in peripheral vision are typically characterized by an undershoot bias. Putting this bias to a test, Kapoula [1] used a paradigm in which observers were presented with two different sets of target eccentricities that partially overlapped each other. Her data were suggestive of a saccadic range effect (SRE): There was a tendency for saccades to overshoot close targets and undershoot far targets in a block, suggesting that there was a response bias towards the center of eccentricities in a given block. Our Experiment 1 was a close replication of the original study by Kapoula [1]. In addition, we tested whether the SRE is sensitive to top-down requirements associated with the task, and we also varied the target presentation duration. In Experiments 1 and 2, we expected to replicate the SRE for a visual discrimination task. The simple visual saccade-targeting task in Experiment 3, entailing minimal top-down influence, was expected to elicit a weaker SRE. Voluntary saccades to remembered target locations in Experiment 3 were expected to elicit the strongest SRE. Contrary to these predictions, we did not observe a SRE in any of the tasks. Our findings complement the results reported by Gillen et al. [2] who failed to find the effect in a saccade-targeting task with a very brief target presentation. Together, these results suggest that unlike arm movements, saccadic eye movements are not biased towards making saccades of a constant, optimal amplitude for the task. |
Marcus Nyström; Dan Witzner Hansen; Richard Andersson; Ignace T. C. Hooge Why have microsaccades become larger? Investigating eye deformations and detection algorithms Journal Article In: Vision Research, vol. 118, pp. 17–24, 2016. @article{Nystroem2016, The reported size of microsaccades is considerably larger today compared to the initial era of microsaccade studies during the 1950s and 1960s. We investigate whether this increase in size is related to the fact that the eye-trackers of today measure different ocular structures than the older techniques, and that the movements of these structures may differ during a microsaccade. In addition, we explore the impact such differences have on subsequent analyzes of the eye-tracker signals. In Experiment I, the movement of the pupil as well as the first and fourth Purkinje reflections were extracted from series of eye images recorded during a fixation task. Results show that the different ocular structures produce different microsaccade signatures. In Experiment II, we found that microsaccade amplitudes computed with a common detection algorithm were larger compared to those reported by two human experts. The main reason was that the overshoots were not systematically detected by the algorithm and therefore not accurately accounted for. We conclude that one reason to why the reported size of microsaccades has increased is due to the larger overshoots produced by the modern pupil-based eye-trackers compared to the systems used in the classical studies, in combination with the lack of a systematic algorithmic treatment of the overshoot. We hope that awareness of these discrepancies in microsaccade dynamics across eye structures will lead to more generally accepted definitions of microsaccades. |
Bartholomäus Odoj; Daniela Balslev Role of oculoproprioception in coding the locus of attention Journal Article In: Journal of Cognitive Neuroscience, vol. 28, no. 3, pp. 517–528, 2016. @article{Odoj2016, The most common neural representations for spatial atten- tion encode locations retinotopically, relative to center of gaze. To keep track of visual objects across saccades or to orient toward sounds, retinotopic representations must be com- bined with information about the rotation of one's own eyes in the orbits. Although gaze input is critical for a correct allo- cation of attention, the source of this input has so far re- mained unidentified. Two main signals are available: corollary discharge (copy of oculomotor command) and oculopro- prioception (feedback from extraocular muscles). Here we asked whether the oculoproprioceptive signal relayed from the somatosensory cortex contributes to coding the locus of attention. We used continuous theta burst stimulation (cTBS) over a human oculoproprioceptive area in the postcentral gyrus (S1EYE). S1EYE-cTBS reduces proprioceptive processing, causing ∼1° underestimation of gaze angle. Participants dis- criminated visual targets whose location was cued in a non- visual modality. Throughout the visual space, S1EYE-cTBS shifted the locus of attention away from the cue by ∼1°, in the same direction and by the same magnitude as the oculo- proprioceptive bias. This systematic shift cannot be attributed to visual mislocalization. Accuracy of open-loop pointing to the same visual targets, a function thought to rely mainly on the corollary discharge, was unchanged. We argue that oculo- proprioception is selective for attention maps. By identifying a potential substrate for the coupling between eye and attention, this study contributes to the theoretical models for spatial attention. |
Sven Ohl; Reinhold Kliegl Revealing the time course of signals influencing the generation of secondary saccades using Aalen's additive hazards model Journal Article In: Vision Research, vol. 124, pp. 52–58, 2016. @article{Ohl2016, Saccadic eye movements are frequently followed by smaller secondary saccades which are generally assumed to correct for the error in primary saccade landing position. However, secondary saccades can also occur after accurate primary saccades and they are often as small as microsaccades, therefore raising the need to further scrutinize the processes involved in secondary saccade generation. Following up a previous study, we analyzed secondary saccades using rate analysis which allows us to quantify experimental effects as shifts in distributions, therefore going beyond comparisons of mean differences. We use Aalen's additive hazards model to delineate the time course of key influences on the secondary saccade rate. In addition to the established effect of primary saccade error, we observed a time-varying influence of under- vs. overshooting - with a higher risk of generating secondary saccades following undershoots. Moreover, increasing target eccentricity influenced the programming of secondary saccades, therefore demonstrating that error-unrelated variables co-determine secondary saccade programs. Our results provide new insights into the generative mechanisms of small saccades during postsaccadic fixation that need to be accounted for by secondary saccade models. |
Sven Ohl; Christian Wohltat; Reinhold Kliegl; Olga Pollatos; Ralf Engbert Microsaccades are coupled to heartbeat Journal Article In: Journal of Neuroscience, vol. 36, no. 4, pp. 1237–1241, 2016. @article{Ohl2016a, During visual fixation, the eye generates microsaccades and slower components of fixational eye movements that are part of the visual processing strategy in humans. Here, we show that ongoing heartbeat is coupled to temporal rate variations in the generation of microsaccades. Using coregistration of eye recording and ECG in humans, we tested the hypothesis that microsaccade onsets are coupled to the relative phase of the R-R intervals in heartbeats. We observed significantly more microsaccades during the early phase after the R peak in the ECG. This form of coupling between heartbeat and eye movements was substantiated by the additional finding of a coupling between heart phase and motion activity in slow fixational eye movements; i.e., retinal image slip caused by physiological drift. Our findings therefore demonstrate a coupling of the oculomotor system and ongoing heartbeat, which provides further evidence for bodily influences on visuomotor functioning. |
Leah Acker; Erica N. Pino; Edward S. Boyden; Robert Desimone FEF inactivation with improved optogenetic methods Journal Article In: Proceedings of the National Academy of Sciences, vol. 113, no. 46, pp. E7297–E7306, 2016. @article{Acker2016, Optogenetic methods have been highly effective for suppressing neural activity and modulating behavior in rodents, but effects have been much smaller in primates, which have much larger brains. Here, we present a suite of technologies to use optogenetics effectively in primates and apply these tools to a classic question in oculomotor control. First, we measured light absorption and heat propagation in vivo, optimized the conditions for using the red-light-shifted halorhodopsin Jaws in primates, and developed a large-volume illuminator to maximize light delivery with minimal heating and tissue displacement. Together, these advances allowed for nearly universal neuronal inactivation across more than 10 mm(3) of the cortex. Using these tools, we demonstrated large behavioral changes (i.e., up to several fold increases in error rate) with relatively low light power densities (≤100 mW/mm(2)) in the frontal eye field (FEF). Pharmacological inactivation studies have shown that the FEF is critical for executing saccades to remembered locations. FEF neurons increase their firing rate during the three epochs of the memory-guided saccade task: visual stimulus presentation, the delay interval, and motor preparation. It is unclear from earlier work, however, whether FEF activity during each epoch is necessary for memory-guided saccade execution. By harnessing the temporal specificity of optogenetics, we found that FEF contributes to memory-guided eye movements during every epoch of the memory-guided saccade task (the visual, delay, and motor periods). |
Rick A. Adams; Markus Bauer; Dimitris Pinotsis; Karl J. Friston Dynamic causal modelling of eye movements during pursuit: Confirming precision-encoding in V1 using MEG Journal Article In: Neuroimage, vol. 132, pp. 175–189, 2016. @article{Adams2016, This paper shows that it is possible to estimate the subjective precision (inverse variance) of Bayesian beliefs during oculomotor pursuit. Subjects viewed a sinusoidal target, with or without random fluctuations in its motion. Eye trajectories and magnetoencephalographic (MEG) data were recorded concurrently. The target was periodically occluded, such that its reappearance caused a visual evoked response field (ERF). Dynamic causal modelling (DCM) was used to fit models of eye trajectories and the ERFs. The DCM for pursuit was based on predictive coding and active inference, and predicts subjects' eye movements based on their (subjective) Bayesian beliefs about target (and eye) motion. The precisions of these hierarchical beliefs can be inferred from behavioural (pursuit) data. The DCM for MEG data used an established biophysical model of neuronal activity that includes parameters for the gain of superficial pyramidal cells, which is thought to encode precision at the neuronal level. Previous studies (using DCM of pursuit data) suggest that noisy target motion increases subjective precision at the sensory level: i.e., subjects attend more to the target's sensory attributes. We compared (noisy motion-induced) changes in the synaptic gain based on the modelling of MEG data to changes in subjective precision estimated using the pursuit data. We demonstrate that imprecise target motion increases the gain of superficial pyramidal cells in V1 (across subjects). Furthermore, increases in sensory precision – inferred by our behavioural DCM – correlate with the increase in gain in V1, across subjects. This is a step towards a fully integrated model of brain computations, cortical responses and behaviour that may provide a useful clinical tool in conditions like schizophrenia. |
Mehmet N. Ağaoğlu; Haluk Öğmen; Susana T. L. Chung Unmasking saccadic uncrowding Journal Article In: Vision Research, vol. 127, pp. 152–164, 2016. @article{Agaoglu2016b, Stimuli that are briefly presented around the time of saccades are often perceived with spatiotemporal distortions. These distortions do not always have deleterious effects on the visibility and identification of a stimulus. Recent studies reported that when a stimulus is the target of an intended saccade, it is released from both masking and crowding. Here, we investigated pre-saccadic changes in single and crowded letter recognition performance in the absence (Experiment 1) and the presence (Experiment 2) of backward masks to determine the extent to which saccadic “uncrowding” and “unmasking” mechanisms are similar. Our results show that pre-saccadic improvements in letter recognition performance are mostly due to the presence of masks and/or stimulus transients which occur after the target is presented. More importantly, we did not find any decrease in crowding strength before impending saccades. A simplified version of a dual-channel neural model, originally proposed to explain masking phenomena, with several saccadic add-on mechanisms, could account for our results in Experiment 1. However, this model falls short in explaining how saccades drastically reduced the effect of backward masking (Experiment 2). The addition of a remapping mechanism that alters the relative spatial positions of stimuli was needed to fully account for the improvements observed when backward masks followed the letter stimuli. Taken together, our results (i) are inconsistent with saccadic uncrowding, (ii) strongly support saccadic unmasking, and (iii) suggest that pre-saccadic letter recognition is modulated by multiple perisaccadic mechanisms with different time courses. |
Nadia Alahyane; Christelle Lemoine-Lardennois; Coline Tailhefer; Thérèse Collins; Jacqueline Fagard; Karine Doré-Mazars Development and learning of saccadic eye movements in 7- to 42-month-old children Journal Article In: Journal of Vision, vol. 16, no. 1, pp. 1–12, 2016. @article{Alahyane2016, From birth, infants move their eyes to explore their environment, interact with it, and progressively develop a multitude of motor and cognitive abilities. The characteristics and development of oculomotor control in early childhood remain poorly understood today. Here, we examined reaction time and amplitude of saccadic eye movements in 93 7- to 42-month-old children while they oriented toward visual animated cartoon characters appearing at unpredictable locations on a computer screen over 140 trials. Results revealed that saccade performance is immature in children compared to a group of adults: Saccade reaction times were longer, and saccade amplitude relative to target location (10° eccentricity) was shorter. Results also indicated that performance is flexible in children. Although saccade reaction time decreased as age increased, suggesting developmental improvements in saccade control, saccade amplitude gradually improved over trials. Moreover, similar to adults, children were able to modify saccade amplitude based on the visual error made in the previous trial. This second set of results suggests that short visual experience and/or rapid sensorimotor learning are functional in children and can also affect saccade performance. |
Tatiana A. Amor; Saulo D. S. Reis; Daniel Campos; Hans J. Herrmann; José S. Andrade Persistence in eye movement during visual search Journal Article In: Scientific Reports, vol. 6, pp. 20815, 2016. @article{Amor2016, As any cognitive task, visual search involves a number of underlying processes that cannot be directly observed and measured. In this way, the movement of the eyes certainly represents the most explicit and closest connection we can get to the inner mechanisms governing this cognitive activity. Here we show that the process of eye movement during visual search, consisting of sequences of fixations intercalated by saccades, exhibits distinctive persistent behaviors. Initially, by focusing on saccadic directions and intersaccadic angles, we disclose that the probability distributions of these measures show a clear preference of participants towards a reading-like mechanism (geometrical persistence), whose features and potential advantages for searching/foraging are discussed. We then perform a Multifractal Detrended Fluctuation Analysis (MF-DFA) over the time series of jump magnitudes in the eye trajectory and find that it exhibits a typical multifractal behavior arising from the sequential combination of saccades and fixations. By inspecting the time series composed of only fixational movements, our results reveal instead a monofractal behavior with a Hurst exponent , which indicates the presence of long-range power-law positive correlations (statistical persistence). We expect that our methodological approach can be adopted as a way to understand persistence and strategy-planning during visual search. |
E. Hainque; E. Apartis; P. M. Daye Switching between two targets with non-constant velocity profiles reveals shared internal model of target motion Journal Article In: European Journal of Neuroscience, vol. 44, no. 8, pp. 2622–2634, 2016. @article{Hainque2016, Several experiments have shown that smooth pursuit and saccades interact while tracking an object moving across the visual scene. It was proposed two decades ago that the amplitude of saccades triggered during smooth pursuit (“catch-up saccades”) were corrected by a delayed sensory signal to account for the ongoing target displacement during catch-up saccades. However recent studies used targets with non-constant velocity profiles and suggested that the correction of catch-up saccade amplitude must be done through an internal model of target motion. It is widely accepted that an internal model of target motion is also used by the central nervous system to cancel inherent delays between visual input and smooth pursuit motor output, ensuring accurate tracking of moving targets. Our study proposes a new paradigm in which the target switches unexpectedly from one target with a non-constant periodic velocity profile to another with a non-constant aperiodic velocity profile. Our results confirm the hypothesis that the central nervous system uses an internal model of target motion to correct catch-up saccade amplitude. In addition, we reconcile the sensory delayed and the internal model of target motion hypotheses and show that a common internal model of target motion is shared within the central nervous system to control smooth pursuit and to correct catch-up saccade amplitude. |
Nina M. Hanning; Donatas Jonikaitis; Heiner Deubel; Martin Szinte Oculomotor selection underlies feature retention in visual working memory Journal Article In: Journal of Neurophysiology, vol. 115, no. 2, pp. 1071–1076, 2016. @article{Hanning2016, Oculomotor selection, spatial task relevance and visual working memory (WM) are described as three processes highly intertwined and sustained by similar cortical structures. However, as task relevant locations always constitute potential saccade targets, no study so far has been able to distinguish between oculomotor selection and spatial task relevance. Here, we designed an experiment that allowed us to dissociate in humans the contribution of task relevance, oculomotor selection and oculomotor execution to the retention of feature representations in WM. We report that task relevance and oculomotor selection lead to dissociable effects on feature WM maintenance. In a first task, in which an objects location was encoded as a saccade target, its feature representations were successfully maintained in WM, while they declined at non-saccade target locations. Likewise, we observed a similar WM benefit at the target of saccades that were prepared but never executed. In a second task, when an objects location was marked as task relevant but constituted a non-saccade target (a location to avoid), feature representations maintained at that location did not benefit. Combined, our results demonstrate that oculomotor selection is consistently associated with WM, whereas task relevance is not. This provides evidence for an overlapping circuitry serving saccade target selection and feature based WM, that can be dissociated from processes encoding task relevant locations. |
Taylor R. Hayes; Alexander A. Petrov Mapping and correcting the influence of gaze position on pupil size measurements Journal Article In: Behavior Research Methods, vol. 48, no. 2, pp. 510–527, 2016. @article{Hayes2016, Pupil size is correlated with a wide variety of important cognitive variables and is increasingly being used by cognitive scientists. Pupil data can be recorded inexpensively and non-invasively by many commonly used video-based eye-tracking cameras. Despite the relative ease of data collection and increasing prevalence of pupil data in the cognitive literature, researchers often underestimate the methodological challenges associated with controlling for confounds that can result in misinterpretation of their data. One serious confound that is often not properly controlled is pupil foreshortening error (PFE)-the foreshortening of the pupil image as the eye rotates away from the camera. Here we systematically map PFE using an artificial eye model and then apply a geometric model correction. Three artificial eyes with different fixed pupil sizes were used to systematically measure changes in pupil size as a function of gaze position with a desktop EyeLink 1000 tracker. A grid-based map of pupil measurements was recorded with each artificial eye across three experimental layouts of the eye-tracking camera and display. Large, systematic deviations in pupil size were observed across all nine maps. The measured PFE was corrected by a geometric model that expressed the foreshortening of the pupil area as a function of the cosine of the angle between the eye-to-camera axis and the eye-to-stimulus axis. The model reduced the root mean squared error of pupil measurements by 82.5 % when the model parameters were pre-set to the physical layout dimensions, and by 97.5 % when they were optimized to fit the empirical error surface. |
Jessica Heeman; Tanja C. W. Nijboer; Nathan Van der Stoep; Jan Theeuwes; Stefan Van der Stigchel Oculomotor interference of bimodal distractors Journal Article In: Vision Research, vol. 123, pp. 46–55, 2016. @article{Heeman2016, When executing an eye movement to a target location, the presence of an irrelevant distracting stimulus can influence the saccade metrics and latency. The present study investigated the influence of distractors of different sensory modalities (i.e. auditory, visual and audiovisual) which were presented at various distances (i.e. close or remote) from a visual target. The interfering effects of a bimodal distractor were more pronounced in the spatial domain than in the temporal domain. The results indicate that the direction of interference depended on the spatial layout of the visual scene. The close bimodal distractor caused the saccade endpoint and saccade trajectory to deviate towards the distractor whereas the remote bimodal distractor caused a deviation away from the distractor. Furthermore, saccade averaging and trajectory deviation evoked by a bimodal distractor was larger compared to the effects evoked by a unimodal distractor. This indicates that a bimodal distractor evoked stronger spatial oculomotor competition compared to a unimodal distractor and that the direction of the interference depended on the distance between the target and the distractor. Together, these findings suggest that the oculomotor vector to irrelevant bimodal input is enhanced and that the interference by multisensory input is stronger compared to unisensory input. |
Stephen J. Heinen; Elena Potapchuk; Scott N. J. Watamaniuk A foveal target increases catch-up saccade frequency during smooth pursuit Journal Article In: Journal of Neurophysiology, vol. 115, no. 3, pp. 1220–1227, 2016. @article{Heinen2016a, Images that move rapidly across the retina of the human eye blur because$backslash$nthe retina has sluggish temporal dynamics. Voluntary smooth pursuit eye movements are modeled as matching object velocity to minimize retinal motion and prevent retinal blurring. However, "catch-up'' saccades that are ubiquitous during pursuit interrupt it and disrupt clear vision. But catch-up saccades may not be a common feature of ocular pursuit, because their existence has been documented with a small moving spot, the classic pursuit stimulus, which is a weak motion stimulus that may poorly emulate larger pursuit objects. We found that spot pursuit does not generalize to that of larger objects. Observers pursued a spot or a larger virtual object with or without a superimposed spot target. Single-spot targets produced lower pursuit acceleration than larger objects. Critically, more saccadic intrusions occurred when stimuli had a central dot, even when position and velocity errors were equated, suggesting that catch-up saccades result from pursuing a single, smallobject or a feature on a large one. To determine what differentiates a large object from a small one, we progressively shrank the featureless virtual object and found that catch-up saccade frequency was highestwhen it fit in the fovea. The results suggest that pursuit of a small target or an object feature recruits a saccade mechanism that does not compensate for a weak motion signal; rather, the target compelsfoveation. Furthermore, catch-up saccades are likely generated by neural circuitry typically used to foveate small objects or features. |
Hinze Hogendoorn Voluntary saccadic eye movements ride the attentional rhythm Journal Article In: Journal of Cognitive Neuroscience, vol. 28, no. 10, pp. 1625–1635, 2016. @article{Hogendoorn2016, Visual perception seems continuous, but recent evidence suggests that the underlying perceptual mechanisms are in fact periodic—particularly visual attention. Because visual attention is closely linked to the preparation of saccadic eye movements, the question arises how periodic attentional processes interact with the preparation and execution of voluntary saccades. In two experiments, human observers made voluntary saccades between two placeholders, monitoring each one for the presentation of a threshold-level target. Detection performance was evaluated as a function of latency with respect to saccade landing. The time course ofdetection performance revealed oscillations at around 4 Hz both before the saccade at the saccade origin and after the saccade at the saccade destination. Furthermore, oscillations before and after the saccade were in phase, meaning that the saccade did not disrupt or reset the ongoing attentional rhythm. Instead, it seems that voluntary saccades are executed as part of an ongoing attentional rhythm, with the eyes in flight during the troughs of the attentional wave. This finding for the first time demonstrates that periodic attentional mechanisms affect not only perception but also overt motor behavior. |
Ignace T. C. Hooge; Kenneth Holmqvist; Marcus Nyström In: Vision Research, vol. 128, pp. 6–18, 2016. @article{Hooge2016, Most modern video eye trackers use the p-CR (pupil minus CR) technique to deal with small relative movements between the eye tracker camera and the eye. We question whether the p-CR technique is appropriate to investigate saccade dynamics. In two experiments we investigated the dynamics of pupil, CR and gaze signals obtained from a standard SMI Hi-Speed eye tracker. We found many differences between the pupil and the CR signals. Differences concern timing of the saccade onset, saccade peak velocity and post-saccadic oscillation (PSO). We also obtained that pupil peak velocities were higher than CR peak velocities. Saccades in the eye trackers' gaze signal (that is constructed from p-CR) appear to be excessive versions of saccades in the pupil signal. We conclude that the pupil-CR technique is not suitable for studying detailed dynamics of eye movements. |
Christoph Huber-Huber; Thomas Ditye; María Marchante Fernández; Ulrich Ansorge Using temporally aligned event-related potentials for the investigation of attention shifts prior to and during saccades Journal Article In: Neuropsychologia, vol. 92, pp. 129–141, 2016. @article{HuberHuber2016, According to the pre-motor theory of attention, attention is shifted to a saccade's landing position before the saccade is executed. Such pre-saccadic attention shifts are usually studied in psychophysical dual-task conditions, with a target-discrimination task before saccade onset. Here, we present a novel approach to investigate pre-saccadic attention shifts with the help of event-related potentials (ERPs). Participants executed one or two saccades to color-defined targets while ERPs and eye-movements were recorded. In single-target blocks participants executed a single saccade. In two-targets blocks participants made either a single saccade to one of the targets, or two successive saccades to both targets. Importantly, in two-targets blocks, targets could appear on the same or on opposite sides of the vertical midline. This allowed us to study contra-to-ipsilateral ERP differences (such as the N2pc or PCN) that reflect attention shifts to the targets, prior to saccade onset and during saccades. If pre-saccadic attention shifts to saccade target locations are necessary for saccade execution and if searched-for saccade targets capture attention, there should be enhanced attentional competition (1) between two targets compared to single targets; (2) between two opposite-sides targets compared to two same-side targets; and (3) in two saccades rather than one saccade conditions: More attentional competition was expected to delay saccade latency and to weaken pre-saccadic laterality effects in ERPs. Hypotheses were tested by means of temporally aligned ERPs that were simultaneously time-locked to stimulus onsets, saccade onsets, and saccade offsets. Predictions (1) and (2) were partly and fully confirmed, respectively, but no evidence was found for (3). We explain the implications of our results for the role of attention during saccade preparation, and we point out how temporally aligned ERPs compare to ICA-based electroencephalogram (EEG) artifact correction procedures and to psychophysical dual-task approaches. |
Sung Jun Joo; Leor N. Katz; Alexander C. Huk Decision-related perturbations of decision-irrelevant eye movements Journal Article In: Proceedings of the National Academy of Sciences, vol. 113, no. 7, pp. 1925–1930, 2016. @article{Joo2016, It is well established that ongoing cognitive functions affect the trajectories of limb movements mediated by corticospinal circuits, suggesting an interaction between cognition and motor action. Although there are also many demonstrations that decision formation is reflected in the ongoing neural activity in oculomotor brain circuits, it is not known whether the decision-related activity in those oculomotor structures interacts with eye movements that are decision irrelevant. Here we tested for an interaction between decisions and instructed saccades unrelated to the perceptual decision. Observers performed a direction-discrimination decisionmaking task, but made decision-irrelevant saccades before registering their motion decision with a button press. Probing the oculomotor circuits with these decision-irrelevant saccades during decision making revealed that saccade reaction times and peak velocities were influenced in proportion to motion strength, and depended on the directional congruence between decisions about visual motion and decision-irrelevant saccades. These interactions disappeared when observers passively viewed the motion stimulus but still made the same instructed saccades, and when manual reaction times were measured instead of saccade reaction times, confirming that these interactions result from decision formation as opposed to visual stimulation, and are specific to the oculomotor system. Our results demonstrate that oculomotor function can be affected by decision formation, even when decisions are communicated without eye movements, and that this interaction has a directionally specific component. These results not only imply a continuous and interactive mixture of motor and decision signals in oculomotor structures, but also suggest nonmotor recruitment of oculomotor machinery in decision making. |
Anna-Maria Kasparbauer; Inga Meyhöfer; Maria Steffens; Bernd Weber; Merve Aydin; Veena Kumari; Rene Hurlemann; Ulrich Ettinger Neural effects of methylphenidate and nicotine during smooth pursuit eye movements Journal Article In: NeuroImage, vol. 141, pp. 52–59, 2016. @article{Kasparbauer2016, Introduction: Nicotine and methylphenidate are putative cognitive enhancers in healthy and patient populations. Although they stimulate different neurotransmitter systems, they have been shown to enhance performance on overlapping measures of attention. So far, there has been no direct comparison of the effects of these two stimulants on behavioural performance or brain function in healthy humans. Here, we directly compare the two compounds using a well-established oculomotor biomarker in order to explore common and distinct behavioural and neural effects. Methods: Eighty-two healthy male non-smokers performed a smooth pursuit eye movement task while lying in an fMRI scanner. In a between-subjects, double-blind design, subjects either received placebo (placebo patch and capsule), nicotine (7 mg nicotine patch and placebo capsule), or methylphenidate (placebo patch and 40 mg methylphenidate capsule). Results: There were no significant drug effects on behavioural measures. At the neural level, methylphenidate elicited higher activation in left frontal eye field compared to nicotine, with an intermediate response under placebo. Discussion: The reduced activation of task-related regions under nicotine could be associated with more efficient neural processing, while increased hemodynamic response under methylphenidate is interpretable as enhanced processing of task-relevant networks. Together, these findings suggest dissociable neural effects of these putative cognitive enhancers. |
Krista R. Kelly; Joost Felius; Santoshi Ramachandran; Blesson A. John; Reed M. Jost; Eileen E. Birch Congenitally impaired disparity vergence in children with infantile Esotropia Journal Article In: Investigative Ophthalmology & Visual Science, vol. 57, no. 6, pp. 2545–2551, 2016. @article{Kelly2016, PURPOSE. We examined whether congenital impairment of disparity vergence in infantile esotropia (ET) exists in children with short duration ET (<=3 months) compared with longduration ET and healthy controls. A short duration of misalignment would allow for a substantial amount of balanced binocular input during the critical period of binocular disparity development. METHODS. A total of 19 children aged 5 to 12 years and treated for infantile ET with a short (<=3 months; n = 10) or long (>=5 months; n = 9) duration of constant misalignment before alignment were enrolled. A total of 22 healthy control children were enrolled as a comparison group. Eye movements during disparity vergence and accommodative vergence were recorded using an EyeLink 1000 binocular eye tracker. Mean response gain was compared between and within groups to determine the effect of duration of misalignment and viewing condition. RESULTS. Compared with controls, children with short (P = 0.002) and long (P <0.001) duration infantile ET had reduced response gains for disparity vergence, but not for accommodative vergence (P = 0.19). CONCLUSIONS. Regardless of duration of misalignment, children with infantile ET had reduced disparity vergence, consistent with a congenital impairment of disparity vergence in infantile ET. Although early correction of misalignment increases the likelihood that some level of binocular disparity sensitivity will be present, normal levels may never be achieved. |
Aarlenne Zein Khan; Douglas P. Munoz; Naomi Takahashi; Gunnar Blohm; Robert M. McPeek Effects of a pretarget distractor on saccade reaction times across space and time in monkeys and humans Journal Article In: Journal of Vision, vol. 16, no. 7, pp. 1–20, 2016. @article{Khan2016, Previous studies have shown that the influence of a behaviorally irrelevant distractor on saccade reaction times (SRTs) varies depending on the temporal and spatial relationship between the distractor and the saccade target. We measured distractor influence on SRTs to a subsequently presented target, varying the spatial location and the timing between the distractor and the target. The distractor appeared at one of four equally eccentric locations, followed by a target (either 50 ms or 200 ms after) at one of 136 different locations encompassing an area of 20° square. We extensively tested two humans and two monkeys on this task to determine interspecies similarities and differences, since monkey neurophysiology is often used to interpret human behavioral findings. Results were similar across species; for the short interval (50 ms), SRTs were shortest to a target presented close to or at the distractor location and increased primarily as a function of the distance from the distractor. There was also an effect of distractor-target direction and visual field. For the long interval (200 ms) the results were inverted; SRTs were longest for short distances between the distractor and target and decreased as a function of distance from distractor. Both SRT patterns were well captured by a two-dimensional dynamic field model with short-distance excitation and long-distance inhibition, based upon known functional connectivity found in the superior colliculus that includes wide-spread excitation and inhibition. Based on these findings, we posit that the different time-dependent patterns of distractor-related SRTs can emerge from the same underlying neuronal mechanisms common to both species. |
Dovin Kiernan; Gerome Manson; Matthew Heath; Luc Tremblay; Timothy N. Welsh Corrections in saccade endpoints scale to the amplitude of target displacements in a double-step paradigm Journal Article In: Neuroscience Letters, vol. 611, pp. 46–50, 2016. @article{Kiernan2016, It is widely held that discrete goal-directed eye movements (saccades) are ballistic in nature because their durations are too short to allow for sensory-based online correction. Recent studies, however, have provided evidence that saccadic endpoints can be mediated via online corrections. Specifically, it has been reported that saccade trajectories adapt to the eccentricity of an unexpectedly perturbed target location (i.e., target 'jump' paradigm). If saccades are subject to online correction mechanisms, then the magnitude of such changes should scale to the amplitude of the target jump. To test this hypothesis, saccadic endpoints for trials on which the target jumped one of three amplitudes (Small: 2.5°, Medium: 5.0°, and Large: 7.5° i.e., Jump trials) immediately after saccade onset were compared with the endpoints of trials in which the target location did not change (i.e., Reference trials). Results showed that primary saccade endpoints for Jump trials were longer than for Reference trials. Importantly, the magnitude of this increase in endpoint scaled with the amplitude of the target jump. Thus, these results support emerging and coalescent evidence that saccade trajectories are subject to online corrections. |