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Saccades move objects of interest into the center of the visual field for high-acuity visual analysis. White, Stritzke, and Gegenfurtner (Current Biology, 18, 124–128, 2008) have shown that saccadic latencies in the context of a structured background are much shorter than those with an unstructured background at equal levels of visibility. This effect has been explained by possible preactivation of the saccadic circuitry whenever a structured background acts as a mask for potential saccade targets. Here, we show that background textures modulate rates of microsaccades during visual fixation. First, after a display change, structured backgrounds induce a stronger decrease of microsaccade rates than do uniform backgrounds. Second, we demonstrate that the occurrence of a microsaccade in a critical time window can delay a subsequent saccadic response. Taken together, our findings suggest that microsaccades contribute to the saccadic facilitation effect, due to a modulation of microsaccade rates by properties of the background., Postprints der Universität Potsdam : Humanwissenschaftliche Reihe, 595

When a visual stimulus is displaced during a saccade the displacement is often not noticed unless it is large compared to the amplitude of the eye movement. Displacement detection is improved, however, if a blank intervenes between saccade target offset and the presentation of the displaced post-saccadic stimulus. This has been interpreted as evidence that precise information about eye position and accurate memory for the position of the pre-saccadic target are available immediately after saccade offset, but are overridden by the presence of the post-saccadic stimulus if it is present when the eyes land. In the current set of experiments we examined in more detail how blanking contributes to the increase in displacement sensitivity. In two experiments we showed that the presentation of a blank interval between saccade offset and the presentation of the displaced stimulus improved people’s ability to detect that the stimulus had been displaced and also their ability to judge the direction that it had been displaced, but only for displacements opposite to the direction of the saccade (backward displacements). A third experiment suggested that this improvement in the detection of backward displacements was due in part to subjects misremembering the saccade target location as being closer to the initial fixation point than it actually was immediately after the saccade but remembering its location more veridically 50 ms later. This has the effect of improving the detection of displacements as well as their direction of displacement, but preferentially for backwards vs. forward displacements.

Gaze-contingent rendering shows promise in improving perceived quality by providing a better match between image quality and the human visual system requirements. For example, information about fixation allows rendering quality to be reduced in peripheral vision, and the additional resources can be used to improve the quality in the foveal region. Gaze-contingent rendering can also be used to compensate for certain limitations of display devices, such as reduced dynamic range or lack of accommodation cues. Despite this potential and the recent drop in the prices of eye trackers, the adoption of such solutions is hampered by system latency which leads to a mismatch between image quality and the actual gaze location. This is especially apparent during fast saccadic movements when the information about gaze location is significantly delayed, and the quality mismatch can be noticed. To address this problem, we suggest a new way of updating images in gaze-contingent rendering during saccades. Instead of rendering according to the current gaze position, our technique predicts where the saccade is likely to end and provides an image for the new fixation location as soon as the prediction is available. While the quality mismatch during the saccade remains unnoticed due to saccadic suppression, a correct image for the new fixation is provided before the fixation is established. This paper describes the derivation of a model for predicting saccade landing positions and demonstrates how it can be used in the context of gaze-contingent rendering to reduce the influence of system latency on the perceived quality. The technique is validated in a series of experiments for various combinations of display frame rate and eye-tracker sampling rate.

Saccades should cause us to see a blur as the eyes sweep across a visual scene. Specific brain mechanisms prevent this by producing suppression during saccades. Neuronal correlates of such suppression were first established in the visual superficial layers of the superior colliculus (SC) and subsequently have been observed in cortical visual areas, including the middle temporal visual area (MT). In this study, we investigated suppression in a recently identified circuit linking visual SC (SCs) to MT through the inferior pulvinar (PI). We examined responses to visual stimuli presented just before saccades to reveal a neuronal correlate of suppression driven by a copy of the saccade command, referred to as a corollary discharge. We found that visual responses were similarly suppressed in SCs, PI, and MT. Within each region, suppression of visual responses occurred with saccades into both visual hemifields, but only in the contralateral hemifield did this suppression consistently begin before the saccade (~100 ms). The consistency of the signal along the circuit led us to hypothesize that the suppression in MT was influenced by input from the SC. We tested this hypothesis in one monkey by inactivating neurons within the SC and found evidence that suppression in MT depends on corollary discharge signals from motor SC (SCi). Combining these results with recent findings in rodents, we propose a complete circuit originating with corollary discharge signals in SCi that produces suppression in visual SCs, PI, and ultimately, MT cortex. NEW & NOTEWORTHY A fundamental puzzle in visual neuroscience is that we frequently make rapid eye movements (saccades) but seldom perceive the visual blur accompanying each movement. We investigated neuronal correlates of this saccadic suppression by recording from and perturbing a recently identified circuit from brainstem to cortex. We found suppression at each stage, with evidence that it was driven by an internally generated signal. We conclude that this circuit contributes to neuronal suppression of visual signals during eye movements.

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.SIGNIFICANCE STATEMENTSaccades are known to produce a suppression of contrast sensitivity at saccadic onset and an enhancement after saccadic offset. Here, we show that these dynamics are systematically embedded in visual oscillations of contrast sensitivity that fluctuate 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 aligning temporally the initiation of the saccade with the visual suppression.

Objective We used a combination of simulation and recordings from human subjects to characterize how saccadic eye movements affect the magnetoencephalogram (MEG). Methods We used simulated saccadic eye movements to generate simulated MEG signals. We also recorded the MEG signals from three healthy adults to 5° magnitude saccades that were vertical up and down, and horizontal left and right. Results The signal elicited by the rotating eye dipoles is highly dependent on saccade direction, can cover a large area, can sometimes have a non-intuitive trajectory, but does not significantly extend above approximately 30 Hz in the frequency domain. In contrast, the saccadic spikes (which are primarily monophasic pulses, but can be biphasic) are highly localized to the lateral frontal regions for all saccade directions, and in the frequency domain extend up past 60 Hz. Conclusions Gamma band saccadic artifact is spatially localized to small regions regardless of saccade direction, but beta band and lower frequency saccadic artifact have broader spatial extents that vary strongly as a function of saccade direction. Significance We have here characterized the MEG saccadic artifact in both the spatial and the frequency domains for saccades of different directions. This could be important in ruling in or ruling out artifact in MEG recordings.

This paper describes the relationship between visual attention and eye blink frequency. In an experiment, we prompted the activation of a subject’s visual attention and examined the influence of visual attention (as measured using electrodermal activity (EDA), which is meaningfully correlated with visual attention) on the subject’s eye blink frequency. Experimental results show that engagement of visual attention decreased eye blink frequency and that when visual attention was not activated, eye blink frequency increased. Knowledge of this relationship provides a technique using EDA to objectively determining a subject’s visual attention status.

In the current study, we examined how the saccadic system responds when visual information changes dynamically in our environment. Previous studies, using the double-step task, have shown that (a) saccade plans could overlap, such that saccade preparation to an object started even while the saccade preparation to another object was ongoing, and (b) saccade plans could be cancelled before they were completed. In these studies, saccade targets were restricted to a few, experimenter-defined locations. Here, we examined whether saccade plan overlap and cancellation mechanisms could be observed in free-viewing conditions. For each trial, we constructed sets of two images, each containing five objects. All objects have unique positions. Image 1 was presented for several fixations, before Image 2 was presented during a fixation, presumably while a saccade plan to an object in Image 1 was ongoing. There were two crucial findings: (a) First, the saccade immediately following the transition was sometimes executed towards objects in Image 2, and not an object in Image 1, suggesting that the earlier saccade plan to an Image 1 object had been cancelled. Second, analysis of the temporal data also suggested that preparation of the first post-transition saccade started before an earlier saccade plan to an Image 1 object was executed, implying that saccade plans overlapped.

The existence of a central fovea, the small retinal region with high analytical performance, is arguably the most prominent design feature of the primate visual system. This centralization comes along with the corresponding capability to move the eyes to reposition the fovea continuously. Past research on visual perception was mainly concerned with foveal vision while the observers kept their eyes stationary. Research on the role of eye movements in visual perception emphasized their negative aspects, for example, the active suppression of vision before and during the execution of saccades. But is the only benefit of our precise eye movement system to provide high acuity of the small foveal region, at the cost of retinal blur during their execution? In this review, I will compare human visual perception with and without saccadic and smooth pursuit eye movements to emphasize different aspects and functions of eye movements. I will show that the interaction between eye movements and visual perception is optimized for the active sampling of information across the visual field and for the calibration of different parts of the visual field. The movements of our eyes and visual information uptake are intricately intertwined. The two processes interact to enable an optimal perception of the world, one that we cannot fully grasp by doing experiments where observers are fixating a small spot on a display.

Psychophysical studies have shown that subjects are often unaware of visual stimuli presented around the time of an eye movement. This saccadic suppression is thought to be a mechanism for maintaining perceptual stability. The brain might accomplish saccadic suppression by reducing the gain of visual responses to specific stimuli or by simply suppressing firing uniformly for all stimuli. Moreover, the suppression might be identical across the visual field or concentrated at specific points. To evaluate these possibilities, we recorded from individual neurons in cortical area V4 of nonhuman primates trained to execute saccadic eye movements. We found that both modes of suppression were evident in the visual responses of these neurons and that the two modes showed different spatial and temporal profiles: while gain changes started earlier and were more widely distributed across visual space, nonspecific suppression was found more often in the peripheral visual field, after the completion of the saccade. Peripheral suppression was also associated with increased noise correlations and stronger local field potential oscillations in the α frequency band. This pattern of results suggests that saccadic suppression shares some of the circuitry responsible for allocating voluntary attention. SIGNIFICANCE STATEMENT We explore our surroundings by looking at things, but each eye movement that we make causes an abrupt shift of the visual input. Why doesn9t the world look like a film recorded on a shaky camera? The answer in part is a brain mechanism called saccadic suppression, which reduces the responses of visual neurons around the time of each eye movement. Here we reveal several new properties of the underlying mechanisms. First, the suppression operates differently in the central and peripheral visual fields. Second, it appears to be controlled by oscillations in the local field potentials at frequencies traditionally associated with attention. These results suggest that saccadic suppression shares the brain circuits responsible for actively ignoring irrelevant stimuli.

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 adaptation trials by 11 % (p

Human observers make large rapid eye movements-saccades-to bring behaviorally relevant information into the fovea, where spatial resolution is high. In some visual tasks [1-4], performance at the location of a saccade target improves before the eyes move. Although these findings provide evidence that extra-retinal signals evoked by saccades can enhance visual perception, it remains unknown whether and how presaccadic modulations change the processing of feature information and thus modulate visual representations. To answer this question, one must go beyond the use of methods that only probe performance accuracy (d') in different tasks. Here, using a psychophysical reverse correlation approach [5-8], we investigated how saccade preparation influences the processing of orientation and spatial frequency-two building blocks of early vision. We found that saccade preparation selectively enhanced the gain of high spatial frequency information and narrowed orientation tuning at the upcoming saccade landing position. These modulations were time locked to saccade onset, peaking right before the eyes moved (-50-0 ms). Moreover, merely deploying covert attention within the same temporal interval without preparing a saccade did not alter performance. The observed presaccadic tuning changes may correspond to the presaccadic enhancement [9-11] and receptive field shifts reported in neurophysiological studies [12-14]. Saccade preparation may support transaccadic integration by reshaping the representation of the saccade target to be more fovea-like just before the eyes move. The presaccadic modulations on spatial frequency and orientation processing illustrate a strong perception-action coupling by revealing that the visual system dynamically reshapes feature selectivity contingent upon eye movements.

Eye movements (saccades) are a necessary component of vision - with a sequence of saccades, we can explore the entire visual scene quickly. The role of saccades is beyond mechanical, in fact they are closely tied to mechanisms of visual cognition, in particular to spatial attention. Two physiological processes, pre-saccadic shifts of attention and saccadic suppression illustrate the interplay of saccades and visual perception: while the attentional shift enhances visual sensitivity to the future saccade target, saccadic suppression inhibits it for non-target objects. Both processes are transient and active already before the saccade onset. So far, these processes have been studied primarily behaviorally in human subjects or via invasive electrophysiological recordings in monkeys. Despite considerable advances, a physiological characterization of these two mechanisms is still lacking in the human literature. Here, we will present a new methodology for investigating perisaccadic events in human subjects. Using electroencephalography (EEG) co-registered with eye tracking (ET), we sampled the complete time-course of perisaccadic activity and identified two ERP components - pre-saccadic voltage enhancement and post-saccadic voltage reduction - that likely relate to shifts of spatial attention and saccadic suppression.

When the head does not move, rapid movements of the eyes called saccades are used to redirect the line of sight. Saccades are defined by a series of metrical and kinematic (evolution of a movement as a function of time) relationships. For example, the amplitude of a saccade made from one visual target to another is roughly 90% of the distance between the initial fixation point (T0) and the peripheral target (T1). However, this stereotypical relationship between saccade amplitude and initial retinal error (|T1-Initial Eye Position|) may be altered, either increased or decreased, by surreptitiously displacing a visual target during an ongoing saccade. This form of saccadic adaptation has been described in both humans and monkeys. We investigated the effects of a contextual cue (target color) on the magnitude of human saccadic adaptation using an eye tracker to measure our subjects' eye position. Our results indicate that target color cannot be used by the eye movement control system to elicit diff...

Previous research shows that human eye movements can serve as a valuable source of information about the structural elements of the oculomotor system and they also can open a window to the neural functions and cognitive mechanisms related to visual attention and perception. The research field of eye movement-driven biometrics explores the extraction of individual-specific characteristics from eye movements and their employment for recognition purposes. In this work, we present a study for the incorporation of dynamic saccadic features into a model of eye movement-driven biometrics. We show that when these features are added to our previous biometric framework and tested on a large database of 322 subjects, the biometric accuracy presents a relative improvement in the range of 31.6--33.5% for the verification scenario, and in range of 22.3--53.1% for the identification scenario. More importantly, this improvement is demonstrated for different types of visual stimulus (random dot, text, video), indicating the enhanced robustness offered by the incorporation of saccadic vigor and acceleration cues.

Understanding the subjective experience of a visually stable world during eye movements has been an important research topic for many years. Various studies were conducted to reveal fundamental mechanisms of this phenomenon. For example, in the paradigm saccadic suppression of displacement (SSD), it has been observed that a small displacement of a saccade target could not easily be reported if this displacement took place during a saccade. New results from Zimmermann et al. (J Neurophysiol 112(12):3066---3076, 2014) show that the effect of being oblivious to small displacements occurs not only during saccades, but also if a mask is introduced while the target is displaced. We address the question of how neurons in the parietal cortex may be connected to each other to account for the SSD effect in experiments involving a saccade and equally well in the absence of an eye movement while perception is disrupted by a mask.

The use of eye-tracking techniques is becoming rapidly extended because of its relevance for acquiring information about cognition and behavior. Recent studies indicate that a correct characterization of the motion of the pupil inside the eyeball is needed, because this motion influences the eye-tracking results. In this work we face this problem and we develop a model that reproduces several findings of recent experiments on saccadic movements. In particular, the dependence of the amplitude and period of the post saccadic oscillations on the saccade size, as well as that of the peak velocity. Our results suggest that post saccadic oscillations could obey mainly to inertial phenomena experimented by the inner part of the iris when the eyeball rotates., 4 pages, 3 figures

Contains fulltext : 151415.pdf (Publisher’s version ) (Open Access) We explore the visual world through saccadic eye movements, but saccades also present a challenge to visual processing by shifting externally stable objects from one retinal location to another. The brain could solve this problem in two ways: by overwriting preceding input and starting afresh with each fixation or by maintaining a representation of presaccadic visual features in working memory and updating it with new information from the remapped location. Crucially, when multiple objects are present in a scene the planning of eye movements profoundly affects the precision of their working memory representations, transferring limited memory resources from fixation toward the saccade target. Here we show that when humans make saccades, it results in an update of not just the precision of representations but also their contents. When multiple item colors are shifted imperceptibly during a saccade the perceived colors are found to fall between presaccadic and postsaccadic values, with the weight given to each input varying continuously with item location, and fixed relative to saccade parameters. Increasing sensory uncertainty, by adding color noise, biases updating toward the more reliable input, which is consistent with an optimal integration of presaccadic working memory with a postsaccadic updating signal. We recover this update signal and show it to be tightly focused on the vicinity of the saccade target. These results reveal how the nervous system accumulates detailed visual information from multiple views of the same object or scene. SIGNIFICANCE STATEMENT This study examines the consequences of saccadic eye movements for the internal representation of visual objects. A saccade shifts the image of a stable visual object from one part of the retina to another. We show that visual representations are built up over these different views of the same object, by combining information obtained before and after each saccade. The weights given to presaccadic and postsaccadic information are determined by the relative reliability of each input. This provides evidence that the visual system combines inputs over time in a statistically optimal way. 8 p.

Saccades operate a continuous selection between competing targets at different locations. This competition has been mostly investigated in the visual context, and it is well known that a visual distractor can interfere with a saccade toward a visual target. Here, we investigated whether multimodal, audio-visual targets confer stronger resilience against visual distraction. Saccades to audio-visual targets had shorter latencies than saccades to unisensory stimuli. This facilitation exceeded the level that could be explained by simple probability summation, indicating that multisensory integration had occurred. The magnitude of inhibition induced by a visual distractor was comparable for saccades to unisensory and multisensory targets, but the duration of the inhibition was shorter for multimodal targets. We conclude that multisensory integration can allow a saccade plan to be reestablished more rapidly following saccadic inhibition.

Developing a valid measurement of visual fatigue induced by 3D display remains a big challenge and is beneficial for optimizing the system design. In this paper, effects of 3D visual fatigue on the dynamics of saccadic eye movements are examined. Thirteen subjects participate in a random dot stereogram (RDS) based task, the performing of the task by the subjects is assumed to directly influence the level of visual fatigue that is evaluated using subjective ratings, optometric tests and eye movement indices. The results of critical fusion frequency (CFF) and accommodation measurement (ACC) show that the proposed experiment setup can induce visual fatigue. According to the subjective ratings, the visual fatigue accumulated in the experiment is mostly related to the binocular vision stress of 3D display. The peak velocity-magnitude relationship of saccadic eye movements decreases after the experiment, and no significant differences are observed in the other saccadic parameters. Our conclusion is that saccadic eye movement, particularly the peak velocity-magnitude relationship, is a sensitive indicator for visual fatigue caused by 3D display and has the potential to help the establishment of a valid on-line measure for the detection of 3D visual fatigue.

A distractor placed nearby a saccade target will cause interference during saccade planning and execution, and as a result will cause the saccade’s trajectory to curve in a systematic way. It has been demonstrated that making a distractor more task-relevant, for example by increasing its similarity to the target, will increase the interference it imposes on the saccade and generate more deviant saccadic trajectories. Is the extent of a distractor’s interference within the oculomotor system limited to its relevance to a particular current task, or can a distractor’s general real-world meaning influence saccade trajectories even when it is made irrelevant within a task? Here, it is tested whether a task-irrelevant distractor can influence saccade trajectory if it depicts a stimulus that is normally socially relevant. Participants made saccades to a target object while also presented with a task-irrelevant (upright or inverted) face, or scrambled non-face equivalent. Results reveal that a distracting face creates greater deviation in saccade trajectory than does a non-face distractor, most notably at longer saccadic reaction times. These results demonstrate the sensitivity of processing that distractors are afforded by the oculomotor system, and support the view that distractor relevance beyond the task itself can also influence saccade planning and execution.

When we explore the visual environment around us, we produce sequences of very precise eye movements aligning the objects of interest with the most sensitive part of the retina for detailed visual processing. A copy of the impending motor command, the corollary discharge, is sent as soon as the first saccade in a sequence is ready to monitor the next fixation location and correctly plan the subsequent eye movement. Neurophysiological investigations have shown that chemical interference with the corollary discharge generates a distinct pattern of spatial errors on sequential eye movements, with similar results also from clinical and TMS studies. Here, we used saccadic inhibition to interfere with the temporal domain of the first of two subsequent saccades during a standard double-step paradigm. In two experiments, we report that the temporal interference on the primary saccade led to a specific error in the final landing position of the second saccade that was consistent with previous lesion and neurophysiological studies, but without affecting the spatial characteristics of the first eye movement. On the other hand, single-step saccades were differently influence by the flash, with a general undershoot, more pronounced for larger saccadic amplitude. These findings show that a flashed visual transient can disrupt saccadic updating in a double-step task, possibly due to the mismatch between the planned and the executed saccadic eye movement.

Made available in DSpace on 2016-03-02T13:04:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2015. Added 1 bitstream(s) on 2016-03-02T13:14:48Z : No. of bitstreams: 1 ISSN1983-3288-2015-08-01-19-27.pdf: 592665 bytes, checksum: 16c463874992e4dc466ab5e23ea30440 (MD5) Saccadic eye movements have been shown to affect posture by decreasing the magnitude of body sway in young adults. However, there is no evidence of how the search for visual information that occurs during eye movements affects postural control in older adults. The purpose of the present study was to determine the influence of saccadic eye movements on postural control in older adults while they stood on 2 different bases of support. Twelve older adults stood upright in 70-s trials under 2 stance conditions (wide and narrow) and 3 gaze conditions (fixation, saccadic eye movements at 0.5 Hz, and saccadic eye movements at 1.1 Hz). Head and trunk sway amplitude and mean sway frequency were measured in both the anterior/posterior (AP) and medial/lateral (ML) directions. The results showed that the amplitude of body sway was reduced during saccades compared with fixation, as previously observed in young adults. However, older adults exhibited similar sway amplitude and frequency in the AP direction under the wide and narrow stance conditions, which is different from observations in young adults, who display larger sway in a narrow stance compared with a wide stance while performing saccades. These results suggest that although older adults are affected by saccadic eye movements by a decrease in the amplitude of body sway, as observed in young adults, they present a more rigid postural control strategy that does not allow larger sway during a more challenging stance condition. Universidade Cruzeiro do Sul, São Paulo, SP, Brasil Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Faculdade de Ciências (FC), Departamento de Educação Física, Av. Eng. Luiz Edmundo Carrijo Coube, 14-01, Vargem Limpa, CEP 17033360, Bauru, SP, Brasil Universidade Federal de São Carlos (UFSCar), Departamento de Educação Física e Motricidade Humana, São Carlos, SP, Brasil Universidade de São Paulo (USP), Escola de Educação Física e Esporte de Ribeirão Preto (EEFERP), Ribeirão Preto, SP, Brasil Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Instituto de Biociências de Rio Claro (IBRC), Departamento de Educação Física, Rio Claro, SP, Brasil Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Faculdade de Ciências (FC), Departamento de Educação Física, Av. Eng. Luiz Edmundo Carrijo Coube, 14-01, Vargem Limpa, CEP 17033360, Bauru, SP, Brasil Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Instituto de Biociências de Rio Claro (IBRC), Departamento de Educação Física, Rio Claro, SP, Brasil

Human vision is characterized by a consistent pattern of saccadic eye movements. With each saccade, internal object representations change their retinal position and spatial resolution. This raises the question as to how peripheral perception is affected by imminent saccadic eye movements. Here, we suggest that saccades are accompanied by a predictionoftheirperceptualconsequences(i.e.,thefoveationofthetargetobject).Accordingly,peripheralperception should be biased toward previously associated foveal input. In this study, we first exposed participants to an altered visualstimulationwhereoneobjectsystematicallychangeditsshapeduringsaccades.Subsequently,participantshad to judge the shape of briefly presented peripheral saccade targets. The results showed that targets were perceived as less curved for objects that previously changed from more circular in the periphery to more triangular in the fovea. Similarly,shapeswereperceivedasmorecurvedforobjectsthatpreviouslychangedfromtriangulartocircular.Thus, peripheral perception seems to depend not solely on the current input but also on memorized experiences, enabling predictions about the perceptual consequences of saccadic eye movements.

Prior oculomotor research has established that saccades tend to land near the center of multiple saccade targets when they are near each other. This saccade averaging phenomenon (or global effect) has been ascribed to short-distance lateral excitation between neurons in the superior colliculus. Further, at greater inter-stimulus distances, eye movements tend toward the individual elements. This transition to control by local elements (individuation) with inter-stimulus distance has been attributed to long-range lateral inhibition between neurons in winner-take-all models of oculomotor behavior. We hypothesized that the traditional method of requiring a saccade to an array of multiple, simultaneous targets may entail response ambiguity that intensifies with distance. We resolved the ambiguity by focussing on reaction time of our human participants to a single saccade target after one or more simultaneous priming stimuli. At a 50-ms prime-target interval, saccadic reaction time was shortest for targets closer to the center of the prime stimuli independent of the distance between the primes. This effect was gone at 400 ms. These findings challenge the typical inferences about the neural control of oculomotor behavior that have been derived from the boundary between saccade averaging and individuation and provide a new method to explore eye movements with lessened impact from decision processes.

Aims: We investigated the performance in scene categorization of patients with Alzheimer's disease (AD) using a saccadic choice task. Method: 24 patients with mild AD, 28 age-matched controls and 26 young people participated in the study. The participants were presented pairs of coloured photographs and were asked to make a saccadic eye movement to the picture corresponding to the target scene (natural vs. urban, indoor vs. outdoor). Results: The patients' performance did not differ from chance for natural scenes. Differences between young and older controls and patients with AD were found in accuracy but not saccadic latency. Conclusions: The results are interpreted in terms of cerebral reorganization in the prefrontal and temporo-occipital cortex of patients with AD, but also in terms of impaired processing of visual global properties of scenes.

In this paper we employ a driven harmonic oscillator to satisfactorily describe data corresponding to ocular movements produced during a visual search task. The data is acquired with an EyeLink 1000. We describe the details of the oscillations in the eye’s rotation angles in between 4 and 40\(^{\circ }\) observed before and after the saccadic and microsaccadic moments. We perform an analysis of the efficiency in the use of the energy of the associated harmonic oscillator.

SummaryThe superior colliculus (SC) is a layered midbrain structure involved in directing eye movements and coordinating visual attention. Electrical stimulation and neuronal recordings in the intermediate layers of monkey SC have shown a retinotopic organization for the mediation of saccadic eye-movements. However, in human SC the topography of saccades is unknown. Here, a novel experimental paradigm and highresolution (1.2-mm) functional magnetic resonance imaging methods were used to measure activity evoked by saccadic eye movements within SC. Results provide three critical observations about the topography of the human SC: (1) saccades along the superior-inferior visual axis are mapped across the medial-lateral anatomy of the SC; (2) the saccadic eye-movement representation is in register with the retinotopic organization of visual stimulation; and (3) activity evoked by saccades occurs deeper within SC than that evoked by visual stimulation. These approaches lay the foundation for studying the organization of human subcortical eye-movement mechanisms.HighlightsHigh-resolution functional MRI enabled imaging from intermediate layers of human SCSaccades along superior-inferior visual field are mapped across medial-lateral SCSaccadic eye movement maps lie deeper in SC and are in alignment with retinotopyeTOC BlurbSavjani et al. found the polar angle representation of saccadic eye movements in human SC. The topography is similar in monkey SC, is in register with the retinotopic organization evoked by visual stimulation, but lies within deeper layers. These methods enable investigation of human subcortical eye-movement organization and visual function.

Reaching is an essential behavior that allows primates to interact with the environment. Precise reaching to visual targets depends on our ability to localize and foveate the target. Despite this, how the saccade system contributes to improvements in reach accuracy remains poorly understood. To assess spatial contributions of eye movements to reach accuracy, we performed a series of behavioral psychophysics experiments in nonhuman primates ( Macaca mulatta). We found that a coordinated saccade with a reach to a remembered target location increases reach accuracy without target foveation. The improvement in reach accuracy was similar to that obtained when the subject had visual information about the location of the current target in the visual periphery and executed the reach while maintaining central fixation. Moreover, we found that the increase in reach accuracy elicited by a coordinated movement involved a spatial coupling mechanism between the saccade and reach movements. We observed significant correlations between the saccade and reach errors for coordinated movements. In contrast, when the eye and arm movements were made to targets in different spatial locations, the magnitude of the error and the degree of correlation between the saccade and reach direction were determined by the spatial location of the eye and the hand targets. Hence, we propose that coordinated movements improve reach accuracy without target foveation due to spatial coupling between the reach and saccade systems. Spatial coupling could arise from a neural mechanism for coordinated visual behavior that involves interacting spatial representations. NEW & NOTEWORTHY How visual spatial representations guiding reach movements involve coordinated saccadic eye movements is unknown. Temporal coupling between the reach and saccade system during coordinated movements improves reach performance. However, the role of spatial coupling is unclear. Using behavioral psychophysics, we found that spatial coupling increases reach accuracy in addition to temporal coupling and visual acuity. These results suggest that a spatial mechanism to couple the reach and saccade systems increases the accuracy of coordinated movements.

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.

The frontal eye field (FEF) is a key brain region to study visuomotor transformations because the primary input to FEF is visual in nature, whereas its output reflects the planning of behaviorally relevant saccadic eye movements. In this study, we used a memory-guided saccade task to temporally dissociate the visual epoch from the saccadic epoch through a delay epoch, and used the local field potential (LFP) along with simultaneously recorded spike data to study the visuomotor transformation process. We showed that visual latency of the LFP preceded spiking activity in the visual epoch, whereas spiking activity preceded LFP activity in the saccade epoch. We also found a spatially tuned elevation in gamma band activity (30-70 Hz), but not in the corresponding spiking activity, only during the delay epoch, whose activity predicted saccade reaction times and the cells' saccade tuning. In contrast, beta band activity (13-30 Hz) showed a nonspatially selective suppression during the saccade epoch. Taken together, these results suggest that motor plans leading to saccades may be generated internally within the FEF from local activity represented by gamma activity.

Manual response times to peripherally presented targets have been reported to be greater in the presence of task-irrelevant pictorial faces at fixation which establish an eye contact with the observer. This effect is interpreted as evidence that direct-gaze faces hold attention. In three experiments, we investigated whether this attention-holding effect is also reflected in saccadic response times. Participants were asked to make a saccade towards a symbolic target that could appear rightwards or leftwards, in the presence of a task-irrelevant centrally placed face with either direct gaze or closed eyes. Unexpectedly, saccadic response times did not show any consistent response pattern as a function of whether the faces were presented with direct gaze vs. closed eyes. Interestingly, saccadic peak velocities were found to be lower in the presence of faces with direct gaze rather than closed eyes (Experiment 1). This effect emerged even in the presence of non-human primate faces (Experiment 2), and no differences between direct gaze and closed eyes emerged when the faces were presented inverted rather than upright (Experiment 3). Overall, these findings suggest that eye contact can have an impact on the saccadic generation system.

This study investigated a novel method of evaluating visually lossy images based on saccadic eye movements. In each trial, participants with normal vision were asked to indicate any visible changes in the image while their gaze positions were being monitored. The original image was replaced with compressed or blurred versions of the same image 150ms after the onset of each eye fixation, and the parameters of the immediately following saccades were assessed. These outcomes were compared to those with a constant rate of image switch (5 Hz flicker) and without switch (control). The resultant rate of visual detection was higher with blurred and constant flickering images than compressed images. Changes in fixation duration, saccade amplitude and peak saccade velocity suggest disrupted visuomotor processes associated with image switch. These disruptions occurred with or without conscious detection. The use of flickering images likely overestimates the probability of detecting lossy image. Analysis of eye movements might be more useful in discerning lossy images in situations where various form factors and visuomotor contexts need to be evaluated.

International audience; The visual perception of human faces by man is fast and efficient compared to that of other categories of objects. Using a saccadic choice task, recent studies showed that participants were able to initiate fast reliable saccades in just 100-110ms toward an image of a human face, when this was presented alongside another image without a face. This extremely fast saccadic reaction time is barely predicted using classical models of visual perception. Thus, the present research investigates whether this result might be explained by the low spatial frequency content of images. Using the same paradigm, with two images simultaneously presented to the left or right visual fields, participants were asked to make a saccade towards a target image. The target was defined as an image belonging to one category: human face, animal or vehicle. The other image corresponded to the distractor and belongs to the other categories. We compared performance to saccade toward one category of target. The two images were displayed either in color, gray-level, low-pass filtered or high-pass filtered. As previous studies, we found that the shortest SRT was observed for saccades towards faces rather than towards animals or vehicles. Analysis of saccadic reaction time distributions showed that, in 130-140ms, participants were able to make more correct than incorrect saccades towards faces for unfiltered (color and gray-level) and low-pass filtered images whereas they needed more time for high-pass filtered images. In contrast, the minimum time participants needed to correctly saccade towards animals and vehicles was longer for low-pass and high-pass filtered than for unfiltered images. The analysis of the image statistics in the Fourier domain revealed that the amplitude spectrum of faces was mainly contained in the low spatial frequencies. Consistent with a coarse-to-fine processing of visual information, our results suggest that extremely fast saccades towards faces could be initiated by low spatial frequencies.

Saccadic eye movements enable us to rapidly direct our high-resolution fovea onto relevant parts of the visual world. However, while we can intentionally select a location as a saccade target, the wider visual scene also influences our executed movements. In the presence of multiple objects, eye movements may be "captured" to the location of a distractor object, or be biased toward the intermediate position between objects (the "global effect"). Here we examined how the relative strengths of the global effect and visual object capture changed with saccade latency, the separation between visual items and stimulus contrast. Importantly, while many previous studies have omitted giving observers explicit instructions, we instructed participants to either saccade to a specified target object or to the midpoint between two stimuli. This allowed us to examine how their explicit movement goal influenced the likelihood that their saccades terminated at either the target, distractor, or intermediate locations. Using a probabilistic mixture model, we found evidence that both visual object capture and the global effect co-occurred at short latencies and declined as latency increased. As object separation increased, capture came to dominate the landing positions of fast saccades, with reduced global effect. Using the mixture model fits, we dissociated the proportion of unavoidably captured saccades to each location from those intentionally directed to the task goal. From this we could extract the time course of competition between automatic capture and intentional targeting. We show that task instructions substantially altered the distribution of saccade landing points, even at the shortest latencies. NEW & NOTEWORTHY: When making an eye movement to a target location, the presence of a nearby distractor can cause the saccade to unintentionally terminate at the distractor itself or the average position in between stimuli. With probabilistic mixture models, we quantified how both unavoidable capture and goal-directed targeting were influenced by changing the task and the target-distractor separation. Using this novel technique, we could extract the time course over which automatic and intentional processes compete for control of saccades.

Humans perform saccadic eye movements two to three times per second. When doing so, the nervous system strongly suppresses sensory feedback for extended periods of time in comparison to movement time. Why does the brain discard so much visual information? Here we suggest that perceptual suppression may arise from efficient sensorimotor computations, assuming that perception and control are fundamentally linked. More precisely, we show theoretically that a Bayesian estimator should reduce the weight of sensory information around the time of saccades, as a result of signal dependent noise and of sensorimotor delays. Such reduction parallels the behavioral suppression occurring prior to and during saccades, and the reduction in neural responses to visual stimuli observed across the visual hierarchy. We suggest that saccadic suppression originates from efficient sensorimotor processing, indicating that the brain shares neural resources for perception and control. DOI: http://dx.doi.org/10.7554/eLife.25073.001, eLife digest Although we have the impression that our eyes move smoothly from place to place, we in fact perform rapid eye movements called saccades several times per second. Experiments have shown that our ability to perceive contrast and flashes decreases before and during each saccade. This phenomenon is known as saccadic suppression. A prevailing hypothesis to explain saccadic suppression suggests that by making vision temporarily less sharp for the rapid eye movement, the nervous system discards visual information about movement and helps us to perceive the world as stable. However, this does not explain the timing of saccadic suppression. Indeed, for saccades of about 50 milliseconds, the brain begins to reduce the sharpness of vision roughly 100 milliseconds before each eye movement begins. Why does the brain discard so much visual input? To answer this question, Crevecoeur and Kording generated a computer model that took into account three properties that previous experiments have detected in animal nervous systems. First, transferring information between the retina and the neurons that control the movement of the eyes involves delays. Second, when neurons generate commands to move the eyes, they also show random fluctuations in activity that increase with the intensity of the commands. And third, visual information can still influence eye movement during a saccade. As a result of incorporating these three properties, the model predicted optimal timings for saccadic suppression that correspond to those that occur in real life. Visual perception and the control of eye movements have often been considered as separate functions of the brain. However, the model generated by Crevecoeur and Kording suggests that perception and the control of eye movement may in fact involve common brain regions. Further research is now needed to investigate predictions made by the model, which should provide new insights into how the brain supports vision. DOI: http://dx.doi.org/10.7554/eLife.25073.002

During natural vision, humans make frequent eye movements but perceive a stable visual world. It is therefore likely that the human visual system contains representations of the visual world that are invariant to eye movements. Here we present an experiment designed to identify visual areas that might contain eye-movement-invariant representations. We used functional MRI to record brain activity from four human subjects who watched natural movies. In one condition subjects were required to fixate steadily, and in the other they were allowed to freely make voluntary eye movements. The movies used in each condition were identical. We reasoned that the brain activity recorded in a visual area that is invariant to eye movement should be similar under fixation and free viewing conditions. In contrast, activity in a visual area that is sensitive to eye movement should differ between fixation and free viewing. We therefore measured the similarity of brain activity across repeated presentations of the same movie within the fixation condition, and separately between the fixation and free viewing conditions. The ratio of these measures was used to determine which brain areas are most likely to contain eye movement-invariant representations. We found that voxels located in early visual areas are strongly affected by eye movements, while voxels in ventral temporal areas are only weakly affected by eye movements. These results suggest that the ventral temporal visual areas contain a stable representation of the visual world that is invariant to eye movements made during natural vision.

Eye movements in hemianopia can serve as an index of perceptual changes, residual visual function, or adaptive changes to altered vision. Central fixations are shifted towards the blind hemifield and saccades into the seeing hemifield are prolonged and less reliable. Targets in the blind hemifield are initially found with an inefficient series of small saccades, but some patients develop a compensatory search hypermetria. Blindsight studies have reported on the accuracy and reliability of saccades or pursuit responses to targets in the blind hemifield, with variable results. How hemianopic subjects scan visual information has been studied with search displays, line bisection and reading. The efficiency of scanning by hemianopic subjects is an important determinant of success in daily life activities such as driving.

Saccades are known to deviate away from distractors, and the amplitude of this deviation seems to reflect the salience of these stimuli, as in the case of human faces. Here, we investigated whether...

The present study investigated the coupling of selection-for-perception and selection-for-action during saccadic eye movement planning in three dual-task experiments. We focused on the effects of spatial congruency of saccade target (ST) location and discrimination target (DT) location and the time between ST-cue and Go-signal (SOA) on saccadic eye movement performance. In two experiments, participants performed a visual discrimination task at a cued location while programming a saccadic eye movement to a cued location. In the third experiment, the discrimination task was not cued and appeared at a random location. Spatial congruency of ST-location and DT-location resulted in enhanced perceptual performance irrespective of SOA. Perceptual performance in spatially incongruent trials was above chance, but only when the DT-location was cued. Saccade accuracy and precision were also affected by spatial congruency showing superior performance when the ST- and DT-location coincided. Saccade latency was only affected by spatial congruency when the DT-cue was predictive of the ST-location. Moreover, saccades consistently curved away from the incongruent DT-locations. Importantly, the effects of spatial congruency on saccade parameters only occurred when the DT-location was cued; therefore, results from experiments 1 and 2 are due to the endogenous allocation of attention to the DT-location and not caused by the salience of the probe. The SOA affected saccade latency showing decreasing latencies with increasing SOA. In conclusion, our results demonstrate that visuospatial attention can be voluntarily distributed upon spatially distinct perceptual and motor goals in dual-task situations, resulting in a decline of visual discrimination and saccade performance.

In a three-dimensional (3D) world most saccades are made towards visual targets that are located at different distances. We previously demonstrated that gaze shifts within 3D space consist of two stages: a target saccade followed by a corrective saccade during gaze fixation that directs the eyes to the physical target location. We proposed that, by accurately positioning the eyes on the visual object, the visual system maintains an orderly representation of the visual world. In this study we used a double saccade experiment to assess the function of corrective saccades in humans. We found that, when a corrective eye movement occurred during fixation on the first target point, the direction of the second saccade towards the next target point was accurate. When a corrective saccade was absent, a directional error of the second target saccade was observed. This finding, which cannot be explained by current models of eye movement control, supports the idea of a two-step model in saccade programming. We suggest that the motor system sends a corollary discharge when programming a corrective saccade for maintaining an orderly representation of the visual world. In conclusion, our results indicate that corrective saccades have a role in programming target saccades within 3D space.

Visual localization during saccadic eye movements is prone to error. Flashes shortly before and after the onset of saccades are usually perceived to shift towards the saccade target, creating a “compression” pattern. Typically, the saccade landing point coincides with a salient saccade target. We investigated whether the mislocalization focus follows the actual saccade landing point or a salient stimulus. Subjects made saccades to either a target or a memorized location without target. In some conditions, another salient marker was presented between the initial fixation and the saccade landing point. The experiments were conducted on both black and picture backgrounds. The results show that: (a) when a saccade target or a marker (spatially separated from the saccade landing point) was present, the compression pattern of mislocalization was significantly stronger than in conditions without them, for both black and picture background conditions, and (b) the mislocalization focus tended towards the salient stimulus regardless of whether it was the saccade target or the marker. Our results suggest that a salient stimulus presented in the scene may have an attracting effect and therefore contribute to the non-uniformity of saccadic mislocalization of a probing flash.

The visual world appears stable despite frequent retinal image movements caused by saccades. Many theories of visual stability assume that extraretinal eye position information is used to spatially adjust perceived locations across saccades, whereas others have proposed that visual stability depends upon coding of the relative positions of objects. McConkie and Currie (1996) proposed a refined combination of these views (called the Saccade Target Object Theory) in which the perception of stability across saccades relies on a local evaluation process centred on the saccade target object rather than on a remapping of the entire scene, with some contribution from memory for the relative positions of objects as well. Three experiments investigated the saccade target object theory, along with an alternative hypothesis that proposes that multiple objects are updated across saccades, but with variable resolution, with the saccade target object (by virtue of being the focus of attention before the saccade and res...

During reading, saccadic eye movements are produced to move the high acuity foveal region of the eye to words of interest for efficient word processing. Distributions of saccadic landing positions peak close to a word's centre but are relatively broad compared to simple oculomotor tasks. Moreover, landing-position distributions are modulated both by distance of the launch site and by saccade type (e.g., one-step saccade, word skipping, refixation). Here we present a mathematical model for the computation of a saccade intended for a given target word. Two fundamental assumptions are related to (1) the sensory computation of the word centre from inter-word spaces and (2) the integration of sensory information and a priori knowledge using Bayesian estimation. Our model was developed for data from a large corpus of eye movements from normal reading. We demonstrate that the model is able simultaneously to account for a systematic shift of saccadic mean landing position with increasing launch-site distance and ...

When scrutinizing the visual world, complex and unexpected stimuli often lead to prolonged eye fixations to enhance cognitive processing, likely by temporarily suppressing a planned saccade. The present study examined whether the suppression signal is tightly linked to a specific planned saccade and if it conforms to the viewer's intention. A novel Go/No-go task was devised where participants made consecutive saccades to fixate a stimulus appearing across the screen horizontal meridian in 4° steps. At times, the features of the stimulus (colour and/or shape) were altered when it reappeared at a new location. Participants had to suppress the saccade that would otherwise leave the stimulus if its features matched instructed criteria. Saccade suppression was determined by the reduced probability for saccades towards and away from a target stimulus. Results show both correct suppression to saccades leaving the target and erroneous suppression to saccades towards it. The erroneous suppression was initially obs...

The visual system conducts parallel and hierarchical signal processing for each aspect of visual information. The different signals are then integrated at appropriate stages to generate unified visual percepts. This ability is a remarkable accomplishment considering that the retinal image is constantly moved by self-motion including movements of body, head, and eyes, so that it contains information about movement from external objects and the observer himself. Our eyes alternate fixation and saccade (rapid and jerky eye movement used to scan the world around us). Therefore, the visual system needs to discriminate this information for an individual to accurately interpret his environment and to prevent the visual images from blurring and bouncing during saccades. In this review, we discuss how the visual system solves these problems at the single neuron level. Results indicate that our visual motion perception is built on the integration of different aspects of visual signals, multisensory signals, and sensory-motor signals along a hierarchy of visual motion information processing.

There is considerable evidence that, when visual stimuli are presented around the time of a saccade, spatial and temporal perceptions of them are distorted. However, only a small number of previous studies have addressed the perception of a visual image induced by a saccade eye movement (visual image that is dynamically drawn on the retina during a saccade at the speed of the eye movement). Here we investigated three-dimensional and temporal perceptions of the saccade-induced images and found that perceptual grouping of objects has a significant effect on the perceived depth and timing of the images.