Academic literature on the topic 'Saccadic suppression'

Perceptual stability is facilitated by a decrease in visual sensitivity during rapid eye movements, called saccadic suppression. While a large body of evidence demonstrates that saccadic programming is plastic, little is known about whether the perceptual consequences of saccades can be modified. Here, we demonstrate that saccadic suppression is attenuated during learning on a standard visual detection-in-noise task, to the point that it is effectively silenced. Across a period of 7 days, 44 participants were trained to detect brief, low-contrast stimuli embedded within dynamic noise, while eye position was tracked. Although instructed to fixate, participants regularly made small fixational saccades. Data were accumulated over a large number of trials, allowing us to assess changes in performance as a function of the temporal proximity of stimuli and saccades. This analysis revealed that improvements in sensitivity over the training period were accompanied by a systematic change in the impact of saccades on performance—robust saccadic suppression on day 1 declined gradually over subsequent days until its magnitude became indistinguishable from zero. This silencing of suppression was not explained by learning-related changes in saccade characteristics and generalized to an untrained retinal location and stimulus orientation. Suppression was restored when learned stimulus timing was perturbed, consistent with the operation of a mechanism that temporarily reduces or eliminates saccadic suppression, but only when it is behaviorally advantageous to do so. Our results indicate that learning can circumvent saccadic suppression to improve performance, without compromising its functional benefits in other viewing contexts.

Saccadic eye movements are made at least 100,000 times each day It is well known that sensitivity to visual input is suppressed during saccades, we examined whether cognitive activity (specifically, mental rotation) is suppressed as well If cognitive processing occurs during saccades, a prime viewed in one fixation should exert a larger influence on a target viewed in a second fixation when a long rather than a short saccade separates their viewing No such effect was found, even though the time difference between long and short saccades was effective in a no-saccade control These results indicate that at least some cognitive operations are suppressed during saccades

Saccades are rapid eye movements that change the direction of gaze, although the full-field image motion associated with these movements is rarely perceived. The attenuation of visual perception during saccades is referred to as saccadic suppression. The mechanisms that produce saccadic suppression are not well understood. We recorded from neurons in the dorsal medial superior temporal area (MSTd) of alert macaque monkeys and compared the neural responses produced by the retinal slip associated with saccades (active motion) to responses evoked by identical motion presented during fixation (passive motion). We provide evidence for a neural correlate of saccadic suppression and expand on two contentious results from previous studies. First, we confirm the finding that some neurons in MSTd reverse their preferred direction during saccades. We quantify this effect by calculating changes in direction tuning index for a large cell population. Second, it has been noted that neural activity associated with saccades can arrive in the parietal cortex ≤30 ms earlier than activity produced by similar visual stimulation during fixation. This led to the question of whether the saccade-related responses were visual in origin or were motor signals arising from saccade-planning areas of the brain. By comparing the responses to saccades made over textured backgrounds of different contrasts, we provide strong evidence that saccade-related responses were visual in origin. Refinements of the possible models of saccadic suppression are discussed.

Burman, Douglas D. and Charles J. Bruce. Suppression of task-related saccades by electrical stimulation in the primate's frontal eye field. J. Neurophysiol. 77: 2252–2267, 1997. Patients with frontal lobe damage have difficulty suppressing reflexive saccades to salient visual stimuli, indicating that frontal lobe neocortex helps to suppress saccades as well as to produce them. In the present study, a role for the frontal eye field (FEF) in suppressing saccades was demonstrated in macaque monkeys by application of intracortical microstimulation during the performance of a visually guided saccade task, a memory prosaccade task, and a memory antisaccade task. A train of low-intensity (20–50 μA) electrical pulses was applied simultaneously with the disappearance of a central fixation target, which was always the cue to initiate a saccade. Trials with and without stimulation were compared, and significantly longer saccade latencies on stimulation trials were considered evidence of suppression. Low-intensity stimulation suppressed task-related saccades at 30 of 77 sites tested. In many cases saccades were suppressed throughout the microstimulation period (usually 450 ms) and then executed shortly after the train ended. Memory-guided saccades were most dramatically suppressed and were often rendered hypometric, whereas visually guided saccades were less severely suppressed by stimulation. At 18 FEF sites, the suppression of saccades was the only observable effect of electrical stimulation. Contraversive saccades were usually more strongly suppressed than ipsiversive ones, and cells recorded at such purely suppressive sites commonly had either foveal receptive fields or postsaccadic responses. At 12 other FEF sites at which saccadic eye movements were elicited at low thresholds, task-related saccades whose vectors differed from that of the electrically elicited saccade were suppressed by electrical stimulation. Such suppression at saccade sites was observed even with currents below the threshold for eliciting saccades. Pure suppression sites tended to be located near or in the fundus, deeper in the anterior bank of the arcuate than elicited saccade sites. Stimulation in the prefrontal association cortex anterior to FEF did not suppress saccades, nor did stimulation in premotor cortex posterior to FEF. These findings indicate that the primate FEF can help orchestrate saccadic eye movements by suppressing inappropriate saccade vectors as well as by selecting, specifying, and triggering appropriate saccades. We hypothesize that saccades could be suppressed both through local FEF interactions and through FEF projections to subcortical regions involved in maintaining fixation.

Primate vision is continuously disrupted by saccadic eye movements, and yet this disruption goes unperceived. One mechanism thought to reduce perception of this self-generated movement is saccadic suppression, a global loss of visual sensitivity just before, during, and after saccadic eye movements. The frontal eye field (FEF) is a candidate source of neural correlates of saccadic suppression previously observed in visual cortex, because it contributes to the generation of visually guided saccades and modulates visual cortical responses. However, whether the FEF exhibits a perisaccadic reduction in visual sensitivity that could be transmitted to visual cortex is unknown. To determine whether the FEF exhibits a signature of saccadic suppression, we recorded the visual responses of FEF neurons to brief, full-field visual probe stimuli presented during fixation and before onset of saccades directed away from the receptive field in rhesus macaques ( Macaca mulatta). We measured visual sensitivity during both epochs and found that it declines before saccade onset. Visual sensitivity was significantly reduced in visual but not visuomotor neurons. This reduced sensitivity was also present in visual neurons with no movement-related modulation during visually guided saccades and thus occurred independently from movement-related activity. Across the population of visual neurons, sensitivity began declining ∼80 ms before saccade onset. We also observed a similar presaccadic reduction in sensitivity to isoluminant, chromatic stimuli. Our results demonstrate that the signaling of visual information by FEF neurons is reduced during saccade preparation, and thus these neurons exhibit a signature of saccadic suppression.

Visual sensitivity is severely impaired during the execution of saccadic eye movements. This phenomenon has been extensively characterized in human psychophysics and nonhuman primate single-neuron studies, but a physiological characterization in humans is less established. Here, we used a method based on steady-state visually evoked potential (SSVEP), an oscillatory brain response to periodic visual stimulation, to examine how saccades affect visual sensitivity. Observers made horizontal saccades back and forth, while horizontal black-and-white gratings flickered at 5–30 Hz in the background. We analyzed EEG epochs with a length of 0.3 s either centered at saccade onset (saccade epochs) or centered at fixations half a second before the saccade (fixation epochs). Compared with fixation epochs, saccade epochs showed a broadband power increase, which most likely resulted from saccade-related EEG activity. The execution of saccades, however, led to an average reduction of 57% in the SSVEP amplitude at the stimulation frequency. This result provides additional evidence for an active saccadic suppression in the early visual cortex in humans. Compared with previous functional MRI and EEG studies, an advantage of this approach lies in its capability to trace the temporal dynamics of neural activity throughout the time course of a saccade. In contrast to previous electrophysiological studies in nonhuman primates, we did not find any evidence for postsaccadic enhancement, even though simulation results show that our method would have been able to detect it. We conclude that SSVEP is a useful technique to investigate the neural correlates of visual perception during saccadic eye movements in humans. NEW & NOTEWORTHY We make fast ballistic saccadic eye movements a few times every second. At the time of saccades, visual sensitivity is severely impaired. The present study uses steady-state visually evoked potentials to reveal a neural correlate of the fine temporal dynamics of these modulations at the time of saccades in humans. We observed a strong reduction (57%) of visually driven neural activity associated with saccades but did not find any evidence for postsaccadic enhancement.

Across saccades, small displacements of a visual target are harder to detect and their directions more difficult to discriminate than during steady fixation. Prominent theories of this effect, known as saccadic suppression of displacement, propose that it is due to a bias to assume object stability across saccades. Recent studies comparing the saccadic effect to masking effects suggest that suppression of displacement is not saccade-specific. Further evidence for this account is presented from two experiments where participants judged the size of displacements on a continuous scale in saccade and mask conditions, with and without blanking. Saccades and masks both reduced the proportion of correctly perceived displacements and increased the proportion of missed displacements. Blanking improved performance in both conditions by reducing the proportion of missed displacements. Thus, if suppression of displacement reflects a bias for stability, it is not a saccade-specific bias, but a more general stability assumption revealed under conditions of impoverished vision. Specifically, I discuss the potentially decisive role of motion or other transient signals for displacement perception. Without transients or motion, the quality of relative position signals is poor, and saccadic and mask-induced suppression of displacement reflects performance when the decision has to be made on these signals alone. Blanking may improve those position signals by providing a transient onset or a longer time to encode the pre-saccadic target position.

Individuals with strabismus frequently show a suppression phenomenon in which part of the visual input in one eye is apparently ignored when both eyes are seeing, although the eye may have normal vision when used monocularly. This is often described as an adaptive response to avoid diplopia. We have examined two patients with microstrabismus (angle of squint less than 5 deg) who show strong suppression but with only mild amblyopia. We studied saccade generation in the two eyes using a red — green anaglyph display which allowed us to present stimuli independently to each eye. When single targets were presented in the suppressing eye, saccadic responses usually occurred. However the latencies of these saccades were increased with respect to those elicited from the normal eye (by about 70 ms for one subject and 270 ms for the other). The amplitudes of the saccades were less consistent than those of the normal eye, and saccades were sometimes made in the opposite direction to the target. We also investigated the remote distractor effect. This effect is found consistently in normal subjects and consists of an increase in the latency of a target-elicited saccade when a distractor is simultaneously presented elsewhere in the visual field. When distractors were presented in the suppressing eye, they had no effect on the latency of saccades to a simultaneous target in the other eye. We conclude that visual stimulation in a suppressing eye has no rapid access to the saccadic system.

When a saccade occurs to an interesting object, visual fixation holds its image on the fovea and suppresses saccades to other objects. Electrical stimulation of the frontal eye field (FEF) has been reported to elicit saccades, and recently also to suppress saccades. This study was performed to characterize properties of the suppression of visually guided (Vsacs) and memory-guided saccades (Msacs) induced by electrical stimulation of the FEF in trained monkeys. For any given stimulation site, we determined the threshold for electrically evoked saccades (Esacs) at ≤50 μA and then examined suppressive effects of stimulation at the same site on Vsacs and Msacs. FEF stimulation suppressed the initiation of both Vsacs and Msacs during and about 50 ms after stimulation at stimulus intensities lower than those for eliciting Esacs, but did not affect the vector of these saccades. Suppression occurred for ipsiversive but not contraversive saccades, and more strongly for saccades with larger amplitudes and those with initial eye positions shifted more in the saccadic direction. The most effective stimulation timing for suppression was about 50 ms before saccade onset, which suggests that suppression occurred in the efferent pathway for generating Vsacs at the premotor rather than the motoneuronal level, most probably in the superior colliculus and/or the paramedian pontine reticular formation. Suppression sites of ipsilateral saccades were distributed over the classical FEF where saccade-related movement neurons were observed. The results suggest that the FEF may play roles in not only generating contraversive saccades but also maintaining visual fixation by suppressing ipsiversive saccades.

Human and nonhuman animal research has outlined the neural regions that support saccadic eye movements. The aim of the current work was to outline the sequence by which distinct neural regions come on-line to support goal-directed saccade execution and error-related feedback. To achieve this, we obtained behavioral responses via eye movement recordings and neural responses via magnetoencephalography (MEG), concurrently, while participants performed an antisaccade task. Neural responses were examined with respect to the onset of the saccadic eye movements. Frontal eye field and visual cortex activity distinguished subsequently successful goal-directed saccades from (correct and erroneous) reflexive saccades prior to the deployment of the eye movement. Activity in the same neural regions following the saccadic movement distinguished correct from incorrect saccadic responses. Error-related activity in the frontal eye fields preceded that from visual regions, suggesting a potential feedback network that may drive corrective eye movements. This work provides the first empirical demonstration of simultaneous remote eyetracking and MEG recording. The coupling of behavioral and neuroimaging technologies, used here to characterize dynamic brain networks underlying saccade execution and error-related feedback, demonstrates a novel within-paradigm converging evidence approach by which to outline the neural underpinnings of cognition.

Considerable evidence indicates that visual sensitivity is reduced during saccadic eye movement. A central question has been whether saccadic suppression results from a non-visual central signal, or whether the obligate image motion that accompanies saccades is itself sufficient to mask vision. In the first of a series of experiments described here, the visual and non-visual effects of saccades were distinguished by measuring contrast sensitivity to luminance modulated low spatial frequency gratings, at 17 cd·m¯² and 0.17 cd·m¯², in saccade conditions and in conditions in which saccade-like image motion was produced by the rotation of a mirror but when observers’ eyes were kept still. The time course of suppression was examined by making measurements from well before image motion began until well after it had ended. A tenfold decrease in contrast sensitivity was found for luminance-modulated gratings with saccades, but little suppression was found with simulated saccades. Adding high contrast noise to the visual display increased the magnitude and the duration of the suppression during simulated saccades but had little effect on suppression produced by real saccades. At lower luminance, suppression was found to be reduced, and its course shallower than at higher luminance. Simulated saccades produced shallower suppression over a longer time course at both higher and lower luminance. In a second experiment the time course of contrast sensitivity to chromatically modulated gratings, at 17 cd·m¯², was examined. No suppression was found; rather there was some evidence of an enhancement of sensitivity, both before and after saccades, relative to fixation conditions. Differences in the effects of real and simulated saccades in the magnitude and time course of sensitivity loss with luminance modulated gratings suggest that saccadic suppression has an extraretinal component that acts on the magnocellular system; the pattern of enhancement found in the later experiment suggests a selective favouring of the parvocellular system both immediately prior to and immediately after saccades. The possibility that the degree of enhancement in sensitivity varies across the visual field was examined using spatially localized stimuli (either high spatial frequency chromatically modulated gratings or letter combinations). Sensitivity was found to decrease at the initial fixation point during the 75 ms prior to saccadic onset and simultaneously to improve at the saccadic target. In the immediate post-saccadic period, sensitivity at the saccadic target was found to exceed that which had been manifest at the initial fixation point prior to saccades, suggesting that post-saccadic enhancement may improve the temporal contrast between one fixation and the next. The final experiments investigated the possibility that our sense of continuity across saccades (as opposed to stability) is influenced by saccade-induced errors in locating events in time. The results of these experiments suggest that saccades can result in errors in judging (a) the time at which external events occur relative to saccadic onset, (b) the temporal order of visual events, and (c) the magnitude of temporal intervals. It is concluded that apparent time is generally foreshortened prior to saccades. This might be due to selective suppression of magnocellular activity and might function to hide saccades and their effects from our awareness. A speculative synthesis is presented based on the idea that recurrent feedback between the neocortical and cortical structures on the one hand, and the thalamic nuclei on the other, has special importance for perception around the time of saccades

Sakkadische Blickbewegungen sind die häufigsten und schnellsten aller menschlichen Bewegungen und führen zur wiederholtem und rapiden Verschiebung von Objektprojektionen über die Retina. Entgegen der verbreiteten Annahme der Suppression untersucht diese Arbeit Ausmaß und Funktion intrasakkadischer visueller Wahrnehmung. Studie I beschreibt eine individuell gefertigte LED-Installation zur ausschließlich intrasakkadischen Präsentation von Text und Bildern, während Studie II einen Algorithmus zur Detektion von Sakkaden vorstellt, welcher blickkontingente Stimulusmanipulationen mithilfe eines DLP Projektionssystems mit einer Bildwiederholungsrate von 1440 Hz ermöglicht. Studien III und IV untersuchten ob visuelle Bewegungsspuren (sog. motion streaks), welche durch die schnelle Bewegung von Objekten über die Retina erzeugt werden, Korrespondenz zwischen Objekten über Sakkaden hinweg herstellen könnten. Diese Bewegungsspuren erlaubten Versuchsteilnehmern nicht nur einen präsakkadischen Stimulus aus zwei identischen postsakkadischen Stimuli zu identifizieren, während diese Fähigkeit von der Deutlichkeit der Bewegungsspur abhing, sondern auch Korrektursakkaden zu einem ursprünglichen präsakkadischen Stimulus zu erleichtern, falls dieser während der Sakkade versetzt wurde. Studie V untersuchte die subjektive Wahrnehmung und Lokalisierung von intrasakkadischen Bewegungsspuren, indem Teilnehmer gezeichnete Berichte angaben. Die Modellierung letzterer ergab, dass retinale Positionssignale mit einer zeitlich gedämpften mentalen Repräsentation von Augenposition kombiniert wurden, um eine Lokalisation in weltzentrierten Koordinaten zu ermöglichen. Diese Ergebnisse legen nahe, dass intrasakkadische visuelle Signale einen Einfluss auf transsakkadische perzeptuelle und motorische Prozesse haben könnten. Letztlich werden die mögliche Funktionen intrasakkadischer Wahrnehmung, sowie Möglichkeiten für zukünftige wissenschaftliche Untersuchungen, diskutiert.<br>Rapid eye movements, so-called saccades, are the fastest and most frequent human movements and cause projections of objects in the world to constantly shift across the retina at high velocities, thereby producing large amounts of motion blur. In contrast to accounts of saccadic suppression, this work explores the extent and potential functional role of intra-saccadic perception. As saccades are fast and brief events, technical challenges were addressed. Study I describes a custom LED-based anorthoscopic presentation setup capable of displaying text and images strictly during saccades. In study II, a novel online saccade detection algorithm enabled rapid, gaze-contingent display changes using a DLP projection system running at 1440 fps. Studies III and IV investigated whether intra-saccadic motion streaks, i.e., blurred traces routinely induced by stimuli moving at saccadic speeds, could serve as cues to establishing object correspondence across saccades. Motion streaks not only enabled perceptual matching of pre- and post-saccadic object locations, while performance depended strongly on streak efficiency, but also facilitated gaze correction in response to intra-saccadic target displacements, that was previously found to be mainly driven by objects’ surface features. Finally, study V explored the subjective appearance and localization of intra-saccadic motion streaks, tasking observers to reproduce their trajectories. Computational modeling of resulting response patterns suggested that retinal positions over time were combined with a damped eye position signal to readily localize intra-saccadic input in world-centered coordinates. Taken together, these results invite the intriguing hypothesis that intra-saccadic visual signals are not discarded from processing and might affect trans-saccadic perceptual and motor processes. The potential role of intra-saccadic perception for active vision, as well as directions for future research, are discussed.

Anatomically, the visual system of non-human primates shows a complicated pattern of cortico-cortical connectivity. The behavioural relevance of many of these connections is unclear, as is the similarity of connectivity with that in the human brain. We used transcranial magnetic stimulation (TMS) and psychophysics to investigate connectivity among visual areas involved in (1) modulating visual perception during saccadic eye movements and (2) perceiving visual motion. Our first study demonstrated that phosphenes induced by TMS of visual cortex are perceived as more intense shortly after the onset of a saccade. This indicates that the cortical areas responsible for saccade generation are connected to those areas responsible for visual perception. Our second study suggested that, when applied with a very short inter-stimulus interval, TMS over an oculomotor region (FEF) can modulate the effect of TMS applied over a region sensitive to visual motion (V5). This suggests a monosynaptic feedback connection from FEF to V5.

The understanding of the subjective experience of a visually stable world despite the occurrence of an observer's eye movements has been the focus of extensive research for over 20 years. These studies have revealed fundamental mechanisms such as anticipatory receptive field (RF) shifts and the saccadic suppression of stimulus displacements, yet there currently exists no single explanatory framework for these observations. We show that a previously presented neuro-computational model of peri-saccadic mislocalization accounts for the phenomenon of predictive remapping and for the observation of saccadic suppression of displacement (SSD). This converging evidence allows us to identify the potential ingredients of perceptual stability that generalize beyond different data sets in a formal physiology-based model. In particular we propose that predictive remapping stabilizes the visual world across saccades by introducing a feedback loop and, as an emergent result, small displacements of stimuli are not noticed by the visual system. The model provides a link from neural dynamics, to neural mechanism and finally to behavior, and thus offers a testable comprehensive framework of visual stability.

Das visuelle System erreicht enorme Verarbeitungsmengen, wenn wir unsere Augen auf ein Objekt richten. Mehrere Prozesse sind aktiv bevor unser Blick das neue Objekt erreicht. Diese Arbeit erforscht die räumlichen und zeitlichen Eigenschaften drei solcher Prozesse: 1. aufmerksamkeitsbedingte Steigerung der neuronalen Aktivität und sakkadische Suppression; 2. aufmerksamkeitsbasierte Auswahl des Zielreizes bei einer visuellen Suchaufgabe; 3. zeitliche Entwicklung der Detektiongenauigkeit bei der Objekt-Substitutionsmaskierung. Wir untersuchten diese Prozesse mit einer Kombination aus humaner Elektroenzephalografie (EEG), eye tracking und psychophysischen Verhaltensmessungen. Zuerst untersuchten wir, wie die neuronale Repräsentation eines Reizes von seiner zeitlichen Nähe zur Sakkade geprägt wird. Wir zeigten, dass direkt vor der Sakkade erscheinende Reize am meisten durch Aufmerksamkeit und Suppression geprägt sind. In Studie 2 wurde die Sichtbarkeit des Reizes mit der Objekt-Substitutionsmaskierung verringert, und wir analysierten das Verhältnis zwischen sakkadischen Reaktionszeiten und ihrer Genauigkeit. Dazu erfassten wir neuronale Marker der Aufmerksamkeitslenkung zum Zielreiz und eine subjektive Bewertung seiner Wahrnehmbarkeit. Wir stellten fest, dass schnelle Sakkaden der Maskierung entgingen und Genauigkeit sowie subjektive Wahrnehmbarkeit erhöhten. Dies zeigt, dass bereits in frühen Verarbeitungsstadien eine bewusste und korrekte Wahrnehmung des Reizes entstehen kann. Wir replizierten diesen Befund für manuelle Antworten, um eine Verfälschung der Ergebnisse durch sakkadenspezifische Prozesse auszuschließen. Neben ihrer theoretischen Bedeutung liefern diese Studien einen methodischen Beitrag zum Forschungsgebiet der EEG-Augenbewegung: Entfernung sakkadischer Artefakte aus dem EEG bzw. Erstellung eines künstlichen Vergleichsdatensatzes. Die Arbeit stellt mehrere Ansätze zur Untersuchung der Dynamik visueller Wahrnehmung sowie Lösungen für zukünftige Studien dar.<br>The visual system achieves a tremendous amount of processing as soon as we set eyes on a new object. Numerous processes are active already before eyes reach the object. This thesis explores the spatio-temporal properties of three such processes: attentional enhancement and saccadic suppression that accompany saccades to target; attentional selection of target in a visual search task; the timecourse of target detection accuracy under object-substitution masking. We monitored these events using a combination of human electrophysiology (EEG), eye tracking and behavioral psychophysics. We first studied how the neural representation of a visual stimulus is affected by its temporal proximity to saccade onset. We show that stimuli immediately preceding a saccade show strongest effects of attentional enhancement and saccadic suppression. Second, using object-substitution masking to reduce visibility, we analyzed the relationship between saccadic reaction times and response accuracy. We also collected subjective visibility ratings and observed neural markers of attentional selection, such as the negative, posterior-contralateral deflection at 200 ms (N2pc). We found that fast saccades escaped the effects of masking, resulted in higher response accuracy and higher awareness ratings. This indicates that early visual processing can trigger awareness and correct behavior. Finally, we replicated this finding with manual responses. Discovering a similar accuracy timecourse in a different modality ruled out saccade-specific mechanisms, such as saccadic suppression and retinal shift, as a potential confound. Next to their theoretical impact, all studies make a methodological contribution to EEG-eye movement research, such as removal of large-scale saccadic artifacts from EEG data and composition of matched surrogate data. In sum, this work uses multiple approaches to describe the dynamics of visual perisaccadic perception and offers solutions for future studies in this field.

L'entrée visuelle rétinienne est discontinue. D'une part les saccades causent un énorme mouvement de l'image sur la rétine 3 à 4 fois par seconde, qui devrait résulter en un floutage des hautes fréquences spatiales et une forte impression de mouvement. D'autre part, les clignements des yeux induisent une diminution temporaire drastique de la luminance toutes les 3 à 4 secondes. Dans des conditions de vision écologiques, ces conséquences visuelles des saccades et des clignements des yeux ne sont pas consciemment perçues et le monde extérieur semble continu et net : deux phénomènes que l'on peut désigner sous le terme d'omission saccadique et d'omission des clignements des yeux. Dans cette thèse, nous avons voulu mieux comprendre comment le système visuel s'accommode de ces interruptions et quels sont les mécanismes qui contribuent à la continuité perceptive autour des saccades et des clignements des yeux. Deux principaux éléments pourraient contribuer à ces omissions : l'entrée visuelle elle-même et un mécanisme extra-rétinien qui informerait le cerveau de l'interruption à venir qui agirait en modifiant le traitement de l'information autour des saccades et des clignements des yeux. Dans une première série d'expériences, nous avons étudié les caractéristiques du masquage du smear saccadique, c'est à dire dans quelle mesure la présence d'images pré et post saccadiques nettes permet de rendre compte de l'omission du smear saccadique. Plus précisément, nous avons élaboré une méthode de mesure objective du masquage du smear et examiné son étendue spatiale et son origine périphérique ou centrale. A l'aide de cette nouvelle méthode, nous avons répliqué les résultats de masquage du smear et mis en évidence que ce masquage a lieu après le site d'interaction binoculaire et résiste à des séparations spatiales entre smear et masque jusqu'à 6 deg. Dans une deuxième étude nous avons comparé la sensibilité à des réseaux sinusoïdaux de basse fréquence spatiale autour des saccades et en fixation lorsque l'entrée visuelle simule les conséquences visuelles des saccades. De plus, nous avons cherché à établir si la plus importante diminution de la sensibilité observée pour de vraies saccades en comparaison des saccades simulées peut être expliquée par les propriétés cinématiques des mouvements oculaires. L'objectif de la troisième étude était de déterminer si le masquage est suffisant pour rendre compte de l'absence de percept de mouvement autour des saccades. Pour ce faire, nous avons présenté en fixation, un stimulus dont le contenu fréquentiel est similaire à celui des scènes naturelles. Ce stimulus était présenté en mouvement avec un profil similaire à celui d'une saccade. Il pouvait être précédé et suivi de l'image statique avant et après le mouvement. Les résultats indiquent que l'amplitude du mouvement perçu diminue considérablement en présence des masques, sans toutefois annuler totalement tout percept de mouvement pour des longues durées de masques. Dans une dernière série d'études nous nous sommes intéressés à la perception de la durée autour des clignements des yeux. Dans la première expérience nous avons quantifié la contribution de la durée d'un clignement des yeux à la durée d'une période d'obscurité plus longue et dans la seconde expérience, nous avons étudié la perception de la durée d'un objet interrompu ou non par un clignement des yeux. Les résultats de ces deux expériences suggèrent l'implication d'un mécanisme extra-rétinien qui supprime la durée perçue de la période d'obscurité causée par les clignements des yeux mais pas la durée des objets visuels chevauchés par le clignement. Pris dans leur ensemble ces résultats précisent notre compréhension des contributions relatives des mécanismes rétiniens et extra-rétiniens à l'omission saccadique et l'omission des clignements des yeux<br>The retinal input is discontinuous. On the one hand saccades, that occur 3-4 times a minute, cause a huge motion of the image on the retina that should result in smearing of the high frequencies of the image and perceived motion. On the other hand eye blinks induce drastic transient decreases in luminance every 3-4 seconds. Under real-world conditions, those visual consequences of saccades and blinks are barely noticed and the world appears continuous and sharp: two phenomena that can be referred to as saccadic and blink omission. In this thesis we were interested in understanding how the visual system deals with these interruptions and which mechanisms contribute to perceived continuity around saccades and blinks. Two main elements could contribute to those omissions: the visual input itself and an extra-retinal mechanism informing the brain of the impending interruption that would affect information processing around saccades and blinks. In a first series of experiments we studied the characteristics of masking of the saccadic smear, the extent to which clear and still pre- and post-saccadic images are responsible for the perceptual omission of saccadic smear. In particular, we designed an objective method to measure smear masking and studied its spatial extent and whether it is of peripheral or central origin. We replicated previous results of saccadic masking with this new method and found that smear masking seems to take place after the site of binocular interaction and survives separations between smear and mask as much as 6 deg. In a second study we compared sensitivity to low-frequency gratings around saccades and in fixation when the visual input simulates the visual consequences of saccades. Moreover we tried to determine whether the greater decrease in sensitivity around real, as compared to simulated, saccades that we found could be accounted for by the cinematic properties of the eye movement. The goal of the third study was to determine if masking was sufficient to explain the lack of perceived motion during saccades. To do that we presented, during fixation, a natural scene-like stimulus moving at saccadic speeds that could be preceded and followed by the initial or final static image. Results indicate that the amplitude of perceived motion considerably decreased in the presence of pre- and post-masks, even though motion was still perceived for long mask durations. In a final series of studies, we probed duration perception around blinks. In a first experiment we quantified the contribution of the duration of a blink to a longer period of darkness and in a second experiment we tested the perceived duration of an object interrupted or not by a blink. Results suggest the involvement of an extra-retinal mechanism that suppresses the perceived duration of the darkness caused by the blink, but not the duration of visual objects that straddle the blink. Taken together these results refine our understanding of the relative contributions of retinal and extra-retinal mechanisms to saccadic and blink omission

Introduction: In gymnastics, athletes perform twisting and flipping skills at high angular velocities. These athletes rely heavily on sensory information from the visual, proprioceptive, and vestibular systems. The vestibulo-ocular reflex (VOR) is responsible for stabilizing the visual field on the retina during head movement. To accomplish this, the eyes are reflexively moved in a direction opposite the head. In a twisting gymnast, this actually reduces the ability of gymnasts to see the landing during airborne skills. Hence it becomes necessary for the gymnasts to cancel or suppress their VOR in order to view the landing. Objective: The purpose of this research is to investigate the relationship between gymnastics skill level and their ability to suppress the VOR. Methods: Ten female gymnasts (mean age 15±2.2) were obtained via a sample of convenience from a local club. The sample included both competitive and recreational gymnasts. Subjects were asked to wear a measurement system that could track head and eye movements as they performed a series of visual tasks. Three experiments were performed: (1) a saccadic experiment – two horizontally fixed LEDs (±10°) were alternately lit in a non-predictable pattern to provide visual cues, (2) a VOR experiment – the subject was asked to perform yawl head movements to an audible metronome beat 11 while visually fixating on an LED target 1m away, and (3) a vestibulo-ocular reflex suppression/cancellation (VORc) experiment – a laser pointer was fixed to the subject‟s helmet close to the cyclopean eye (slaving the target to the head movement) and the subject was again asked to perform head movements to a metronome while visually fixating on the target. In both VOR experiments, the metronome frequency varied from 72 to 196 beats per minute. Eye and head position data were synchronously sampled at 250 and 100Hz respectively. Data were post-processed using MATLAB. Periodic calibrations were performed throughout the experiment to test the continued reliability of the data. Results: Saccadic peak velocities and latencies were calculated for the sample population. Their performance did not differ from the normal population. VOR and VORc gains were also calculated and compared. The higher level (competitive) gymnasts were better at suppressing their VOR. In addition, left/right VOR gain asymmetries correlated highly with twist direction in seven of the competitive gymnasts. Discussion/Conclusions: There is a correlation between VOR performance and gymnastic level. These results do not suggest that VOR differences develop as a result of practice. These differences may simply allow some individuals to become better performers. A longitudinal study on a larger population would be required to test the causal relationship between these variables.

When the eye rotates, switching from one fixation point to another, the perception of motion is strongly suppressed and rarely perceived. During these quick ‘saccadic’ eye movements, other aspects of visual perception become suppressed or compressed as well, with certain effects being stronger or weaker along the plane of the saccade - such differences can help identify the underlying neuronal pathways, since some exhibit directional tuning (e.g. neurons projecting from primate V1 to middle temporal area (MT)), and others do not (e.g. relay neurons linking the superior colliculus to area MT). A briefly presented motion probe was placed at a number of points relative to saccade to plot sensitivity to motion along different planes and directions. The results suggest that saccadic motion is suppressed before the eye begins to move, and is applied evenly across planes and directions.