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Visual neural processing is distributed among a multitude of sensory and sensory-motor brain areas exhibiting varying degrees of functional specializations and spatial representational anisotropies. Such diversity raises the question of how perceptual performance is determined, at any one moment in time, during natural active visual behavior. Here, exploiting a known dichotomy between the primary visual cortex and superior colliculus in representing either the upper or lower visual field, we asked whether peri-saccadic visual sensitivity is dominated by one or the other spatial anisotropy. Humans detected peri-saccadic upper visual field stimuli significantly better than lower visual field stimuli, contrary to known perceptual superiority in the lower visual field during steady-state gaze fixation. Consistent with this, peri-saccadic superior colliculus visual responses were also significantly stronger in the upper visual field than in the lower visual field. Thus, peri-saccadic visual sensitivity reflects oculomotor, rather than visual, map spatial anisotropies.

Visual transients can interrupt overt orienting by abolishing the execution of a planned eye movement due about 90 ms later, a phenomenon known as saccadic inhibition (SI). It is not known if the same inhibitory process might influence covert orienting in the absence of saccades, and consequently alter visual perception. In Experiment 1 (n = 14), we measured orientation discrimination during a covert orienting task in which an uninformative exogenous visual cue preceded the onset of an oriented probe by 140–290 ms. In half of the trials, the onset of the probe was accompanied by a brief irrelevant flash, a visual transient that would normally induce SI. We report a time-dependent inhibition of covert orienting in which the irrelevant flash impaired orientation discrimination accuracy when the probe followed the cue by 190 and 240 ms. The interference was more pronounced when the cue was incongruent with the probe location, suggesting an impact on the reorienting component of the attentional shift. In Experiment 2 (n = 12), we tested whether the inhibitory effect of the flash could occur within an earlier time range, or only within the later, reorienting range. We presented probes at congruent cue locations in a time window between 50 and 200 ms. Similar to Experiment 1, discrimination performance was altered at 200 ms after the cue. We suggest that covert attention may be susceptible to similar inhibitory mechanisms that generate SI, especially in later stages of attentional shifting (> 200 ms after a cue), typically associated with reorienting.

Microsaccades have a steady rate of occurrence during maintained gaze fixation, which gets transiently modulated by abrupt sensory stimuli. Such modulation, characterized by a rapid reduction in microsaccade frequency followed by a stronger rebound phase of high microsaccade rate, is often described as the microsaccadic rate signature, owing to its stereotyped nature. Here, we investigated the impacts of stimulus polarity (luminance increments or luminance decrements relative to background luminance) and size on the microsaccadic rate signature. We presented brief, behaviorally irrelevant visual flashes consisting of large or small, white or black stimuli over an otherwise gray image background. Both large and small stimuli caused robust early microsaccadic inhibition, but postinhibition microsaccade rate rebound was significantly delayed and weakened for large stimuli when compared with small ones. Critically, small black stimuli were associated with stronger modulations in the microsaccade rate signature than small white stimuli, particularly in the postinhibition rebound phase, and black stimuli also amplified the incidence of early stimulus-directed microsaccades. Our results demonstrate that the microsaccadic rate signature is sensitive to stimulus size and polarity, and they point to dissociable neural mechanisms underlying early microsaccadic inhibition after stimulus onset and later microsaccadic rate rebound at longer times thereafter. These results also demonstrate early access of oculomotor control circuitry to diverse sensory representations, particularly for momentarily inhibiting saccade generation with short latencies.

A key feature of visual processing in humans is the use of saccadic eye movements to look around the environment. Saccades are typically used to bring relevant information, which is glimpsed with extrafoveal vision, into the high-resolution fovea for further processing. With the exception of some unusual circumstances, such as the first fixation when walking into a room, our saccades are mainly guided based on this extrafoveal preview. In contrast, the majority of experimental studies in vision science have investigated "passive" behavioral and neural responses to suddenly appearing and often temporally or spatially unpredictable stimuli. As reviewed here, a growing number of studies have investigated visual processing of objects under more natural viewing conditions in which observers move their eyes to a stationary stimulus, visible previously in extrafoveal vision, during each trial. These studies demonstrate that the extrafoveal preview has a profound influence on visual processing of objects, both for behavior and neural activity. Starting from the preview effect in reading research we follow subsequent developments in vision research more generally and finally argue that taking such evidence seriously leads to a reconceptualization of the nature of human visual perception that incorporates the strong influence of prediction and action on sensory processing. We review theoretical perspectives on visual perception under naturalistic viewing conditions, including theories of active vision, active sensing, and sampling. Although the extrafoveal preview paradigm has already provided useful information about the timing of, and potential mechanisms for, the close interaction of the oculomotor and visual systems while reading and in natural scenes, the findings thus far also raise many new questions for future research.

At any moment in time, new information is sampled from the environment and interacts with ongoing brain state. Often, such interaction takes place within individual circuits that are capable of both mediating the internally ongoing plan as well as representing exogenous sensory events. Here we investigated how sensory-driven neural activity can be integrated, very often in the same neuron types, into ongoing oculomotor commands for saccades. Despite the ballistic nature of saccades, visually-induced action potentials in the superior colliculus (SC), a structure known to drive eye movements, not only occurred intra-saccadically, but they were also associated with highly predictable modifications of ongoing eye movements. Such predictable modifications reflected a simultaneity of movement-related discharge at one SC site and visually-induced activity at another. Our results suggest instantaneous readout of the SC map during movement generation, irrespective of activity source, and they explain a significant component of kinematic variability of motor outputs.

The eyes are never still during maintained gaze fixation. When microsaccades are not occurring, ocular position exhibits continuous slow changes, often referred to as drifts. Unlike microsaccades, drifts remain to be viewed as largely random eye movements. Here we found that ocular position drifts can, instead, be very systematically stimulus-driven, and with very short latencies. We used highly precise eye tracking in three well trained macaque monkeys and found that even fleeting (~8 ms duration) stimulus presentations can robustly trigger transient and stimulus-specific modulations of ocular position drifts, and with only approximately 60 ms latency. Such drift responses are binocular, and they are most effectively elicited with large stimuli of low spatial frequency. Intriguingly, the drift responses exhibit some image pattern selectivity, and they are not explained by convergence responses, pupil constrictions, head movements, or starting eye positions. Ocular position drifts have very rapid access to exogenous visual information., eLife digest Vision is a highly complex, active process. As we observe and interact with the world around us, we constantly use eye movements to capture the visual information we need. In fact, our eyes continue to make tiny, unconscious movements even when we try to fix our gaze on something. There are two main types of tiny eye movements. The first kind, so called microsaccades, are fast, microscopic flicks that happen every second or half-second. The other kind, termed drift, is a slower, gradual motion that takes place between microsaccades, or at any time when other eye movements are not happening. However, we know far less about drifts than about any other eye movements: both the reason why they occur and the brain mechanisms controlling them are still unclear. Many scientists think that drifts are largely random movements, without any set direction. However, eye drifts do sometimes align with other behaviours – for example, they can help compensate for small, subtle head movements – suggesting that drifts may not be completely random after all. Malevich, Buonocore and Hafed therefore set out to test the hypothesis that eye drifts could, under the right circumstances, in fact be highly directed movements. These experiments used precise sensors to track eye movements in macaque monkeys, which had been trained to fix their gaze on images or shapes (stimuli) presented on a screen. This revealed that presenting new stimuli, even for a few thousandths of a second, could repeatedly trigger drifts. This reaction also happened quickly, starting less than one hundredth of a second after presentation of the stimulus. Further tests, using different images, revealed that the drifts were not only simply reacting to any new stimuli but also appeared to be a partially selective response to specific types of images. These tended to have larger features and less fine detail. For example, a picture of a landscape with large swaths of sky or hilltops would much more reliably trigger the eye drifts than a finely detailed checkerboard pattern, with many small squares alternating between black and white. These results suggested that drifts, far from being random movements, could be another tool for the brain to process visual information. This work sheds new light on the potential role of eye movements in vision, and adds another layer of complexity to the question of how we see. Malevich et al. hope that this study will inspire further research into the brain mechanisms behind ocular drifts.

Visual transients can interrupt overt orienting by abolishing the execution of a planned eye movement due about 90 ms later, a phenomenon known as saccadic inhibition (SI). It is not known if the same inhibitory process might influence covert orienting in the absence of saccades, and consequently alter visual perception. In Experiment 1 (n=14), we measured orientation discrimination during a covert orienting task in which an uninformative exogenous visual cue preceded the onset of an oriented probe by 140 to 290 ms. In half of the trials the onset of the probe was accompanied by a brief irrelevant flash, a visual transient that would normally induce SI. We report a time-dependent inhibition of covert orienting in which the irrelevant flash impaired orientation discrimination accuracy when the probe followed the cue by 190 and 240 ms. The interference was more pronounced when the cue was incongruent with the probe location, suggesting an impact on the reorienting component of the attentional shift. In Experiment 2 (n=12), we tested whether the inhibitory effect of the flash could occur within an earlier time range, or only within the later, reorienting range. We presented probes at congruent cue locations in a time window between 50 to 200 ms. Similarly to Experiment 1, discrimination performance was altered at 200 ms after the cue. We suggest that covert attention may be susceptible to similar inhibitory mechanisms that generate SI, especially in later stages of attentional shifting (> 200ms after a cue), typically associated with reorienting.

Covert and overt spatial selection behaviors are guided by both visual saliency maps derived from early visual features as well as priority maps reflecting high-level cognitive factors. However, whether mid-level perceptual processes associated with visual form recognition contribute to covert and overt spatial selection behaviors remains unclear. We hypothesized that if peripheral visual forms contribute to spatial selection behaviors, then they should do so even when the visual forms are task-irrelevant. We tested this hypothesis in male and female human subjects as well as in male macaque monkeys performing a visual detection task. In this task, subjects reported the detection of a supra-threshold target spot presented on top of one of two peripheral images, and they did so with either a speeded manual button press (humans) or a speeded saccadic eye movement response (humans and monkeys). Crucially, the two images, one with a visual form and the other with a partially phase-scrambled visual form, were completely irrelevant to the task. In both manual (covert) and oculomotor (overt) response modalities, and in both humans and monkeys, response times were faster when the target was congruent with a visual form than when it was incongruent. Importantly, incongruent targets were associated with almost all errors, suggesting that forms automatically captured selection behaviors. These findings demonstrate that mid-level perceptual processes associated with visual form recognition contribute to covert and overt spatial selection. This indicates that neural circuits associated with target selection, such as the superior colliculus, may have privileged access to visual form information.Significance statementSpatial selection of visual information either with (overt) or without (covert) foveating eye movements is critical to primate behavior. However, it is still not clear whether spatial maps in sensorimotor regions known to guide overt and covert spatial selection are influenced by peripheral visual forms. We probed the ability of humans and monkeys to perform overt and covert target selection in the presence of spatially congruent or incongruent visual forms. Even when completely task-irrelevant, images of visual objects had a dramatic effect on target selection, acting much like spatial cues used in spatial attention tasks. Our results demonstrate that traditional brain circuits for orienting behaviors, such as the superior colliculus, likely have privileged access to visual object representations.

Microsaccades have a steady rate of occurrence during maintained gaze fixation, which gets transiently modulated by abrupt sensory stimuli. Such modulation, characterized by a rapid reduction in microsaccade frequency followed by a stronger rebound phase of high microsaccade rate, is often described as the microsaccadic rate signature, owing to its stereotyped nature. Here we investigated the impacts of stimulus polarity (luminance increments or luminance decrements relative to background luminance) and size on the microsaccadic rate signature. We presented brief visual flashes consisting of large or small white or black stimuli over an otherwise gray image background. Both large and small stimuli caused robust early microsaccadic inhibition, but only small ones caused a subsequent increase in microsaccade frequency above baseline microsaccade rate. Critically, small black stimuli were always associated with stronger modulations in microsaccade rate after stimulus onset than small white stimuli, particularly in the post-inhibition rebound phase of the microsaccadic rate signature. Because small stimuli were also associated with expected direction oscillations to and away from their locations of appearance, these stronger rate modulations in the rebound phase meant higher likelihoods of microsaccades opposite the black flash locations relative to the white flash locations. Our results demonstrate that the microsaccadic rate signature is sensitive to stimulus polarity, and they point to dissociable neural mechanisms underlying early microsaccadic inhibition after stimulus onset and later microsaccadic rate rebound at longer times thereafter. These results also demonstrate early access of oculomotor control circuitry to sensory representations, particularly for momentarily inhibiting saccade generation.New and noteworthyMicrosaccades are small saccades that occur during gaze fixation. Microsaccade rate is transiently reduced after sudden stimulus onsets, and then strongly rebounds before returning to baseline. We explored the influence of stimulus polarity (black versus white) on this “rate signature”. We found that small black stimuli cause stronger microsaccadic modulations than white ones, but primarily in the rebound phase. This suggests dissociated neural mechanisms for microsaccadic inhibition and subsequent rebound in the microsaccadic rate signature.

Microsaccades occur during gaze fixation to correct for miniscule foveal motor errors. The mechanisms governing such fine oculomotor control are still not fully understood. In this study, we explored microsaccade control by analyzing the impacts of transient visual stimuli on these movements’ kinematics. We found that such kinematics can be altered in systematic ways depending on the timing and spatial geometry of visual transients relative to the movement goals. In two male rhesus macaques, we presented peripheral or foveal visual transients during an otherwise stable period of fixation. Such transients resulted in well-known reductions in microsaccade frequency, and our goal was to investigate whether microsaccade kinematics would additionally be altered. We found that both microsaccade timing and amplitude were modulated by the visual transients, and in predictable manners by these transients’ timing and geometry. Interestingly, modulations in the peak velocity of the same movements were not proportional to the observed amplitude modulations, suggesting a violation of the well-known “main sequence” relationship between microsaccade amplitude and peak velocity. We hypothesize that visual stimulation during movement preparation affects not only the saccadic “Go” system driving eye movements but also a “Pause” system inhibiting them. If the Pause system happens to be already turned off despite the new visual input, movement kinematics can be altered by the readout of additional visually evoked spikes in the Go system coding for the flash location. Our results demonstrate precise control over individual microscopic saccades and provide testable hypotheses for mechanisms of saccade control in general. NEW & NOTEWORTHY Microsaccadic eye movements play an important role in several aspects of visual perception and cognition. However, the mechanisms for microsaccade control are still not fully understood. We found that microsaccade kinematics can be altered in a systematic manner by visual transients, revealing a previously unappreciated and exquisite level of control by the oculomotor system of even the smallest saccades. Our results suggest precise temporal interaction between visual, motor, and inhibitory signals in microsaccade control.

Humans actively sample their environment with saccadic eye movements to bring relevant information into high-acuity foveal vision. Despite being lower in resolution, peripheral information is also available prior to each saccade. How pre-saccadic extrafoveal preview of a visual object influences its post-saccadic processing is still an unanswered question. Here, we investigated this question by simultaneously recording behavior and fixation-related brain potentials while human subjects made saccades to face stimuli. We manipulated the relationship between pre-saccadic “previews” and post-saccadic images to explicitly isolate the influences of the former. Subjects performed a gender discrimination task on a newly foveated face under three preview conditions: phase-scrambled face, incongruent face (different identity from the foveated face), and congruent face (same identity). As expected, reaction times were faster after a congruent-face preview compared to the phase-scrambled and incongruent conditions. Importantly, a face preview (either incongruent or congruent) resulted in a strong reduction of post-saccadic neural responses. Specifically, we analyzed the classic face-selective N170 component at occipito-temporal EEG electrodes, which was still present in our experiments with active looking. We found that this component was strongly attenuated for face preview conditions compared to scrambled conditions. This large and long-lasting decrease in evoked activity is consistent with an active prediction mechanism influencing category-specific neural processing at the start of a new fixation. These findings constrain theories of visual stability and show that the extrafoveal preview methodology can be a useful tool to investigate its underlying mechanisms.Significance StatementNeural correlates of object recognition have traditionally been studied by flashing stimuli to the central visual field. This procedure differs in fundamental ways from natural vision, where viewers actively sample the environment with eye movements and also obtain a low-resolution preview of soon-to-be-fixated objects. Here we show that the N170, a classic electrophysiological marker of the structural processing of faces, also occurs during a more natural viewing condition but is massively reduced due to extrafoveal preprocessing (preview benefit). Our results therefore highlight the importance of peripheral vision during trans-saccadic processing in building a coherent and stable representation of the world around us.

The oculomotor system integrates a variety of visual signals into appropriate motor plans, but such integration can have widely varying time scales. For example, smooth pursuit eye movements to follow a moving target are slower and longer lasting than saccadic eye movements and it has been suggested that initiating a smooth pursuit eye movement involves an obligatory “open-loop” interval in which new visual motion signals presumably cannot influence the ensuing motor plan for up to 100 ms after movement initiation. However, this view is contrary to the idea that the oculomotor periphery has privileged access to short-latency visual signals. Here, we show that smooth pursuit initiation is sensitive to visual inputs, even in open-loop intervals. We instructed male rhesus macaque monkeys to initiate saccade-free smooth pursuit eye movements and injected a transient, instantaneous eye position error signal at different times relative to movement initiation. We found robust short-latency modulations in eye velocity and acceleration, starting only ∼50 ms after transient signal occurrence and even during open-loop pursuit initiation. Critically, the spatial direction of the injected position error signal had predictable effects on smooth pursuit initiation, with forward errors increasing eye acceleration and backward errors reducing it. Catch-up saccade frequencies and amplitudes were also similarly altered ∼50 ms after transient signals, much like the well known effects on microsaccades during fixation. Our results demonstrate that smooth pursuit initiation is highly sensitive to visual signals and that catch-up saccade generation is reset after a visual transient.SIGNIFICANCE STATEMENTSmooth pursuit eye movements allow us to track moving objects. The first ∼100 ms of smooth pursuit initiation are characterized by smooth eye acceleration and are overwhelmingly described as being “open-loop”; that is, unmodifiable by new visual motion signals. We found that all phases of smooth pursuit, including the so-called open-loop intervals, are reliably modifiable by visual signals. We injected transient flashes resulting in very brief, spatially specific position error signals to smooth pursuit and observed very short-latency changes in smooth eye movements to minimize such errors. Our results highlight the flexibility of the oculomotor system in reacting to environmental events and suggest a functional role for the pervasiveness of visual sensitivity in oculomotor control brain regions.

Despite strong evidence to the contrary in the literature, microsaccades are overwhelmingly described as involuntary eye movements. Here we show in both human subjects and monkeys that individual microsaccades of any direction can easily be triggered: (1) on demand, based on an arbitrary instruction, (2) without any special training, (3) without visual guidance by a stimulus, and (4) in a spatially and temporally accurate manner. Subjects voluntarily generated instructed “memory-guided” microsaccades readily, and similarly to how they made normal visually-guided ones. In two monkeys, we also observed midbrain superior colliculus neurons that exhibit movement-related activity bursts exclusively for memory-guided microsaccades, but not for similarly-sized visually-guided movements. Our results demonstrate behavioral and neural evidence for voluntary control over individual microsaccades, supporting recently discovered functional contributions of individual microsaccade generation to visual performance alterations and covert visual selection, as well as observations that microsaccades optimize eye position during high acuity visually-guided behavior., Microsaccades are small-amplitude, fixational eye movements that are largely thought to be involuntary. Here, the authors demonstrate that monkeys (and humans) can be easily trained to respond to a remembered target location with a volitional microsaccade, and that a population of superior colliculus neurons is selectively associated with them.

Two main types of small eye movements occur during gaze fixation: microsaccades and slow ocular drifts. While microsaccade generation has been relatively well studied, ocular drift control mechanisms are unknown. Here we explored the degree to which monkey smooth eye movements, on the velocity scale of slow ocular drifts, can be generated systematically. Two male rhesus macaque monkeys tracked a spot moving sinusoidally, but slowly, along the horizontal or vertical direction. Maximum target displacement in the motion trajectory was 30 min arc (0.5°), and we varied the temporal frequency of target motion from 0.2 to 5 Hz. We obtained an oculomotor “transfer function” by measuring smooth eye velocity gain (relative to target velocity) as a function of frequency, similar to past work with large-amplitude pursuit. Monkey eye velocities as slow as those observed during slow ocular drifts were clearly target motion driven. Moreover, as with large-amplitude smooth pursuit, eye velocity gain varied with temporal frequency. However, unlike with large-amplitude pursuit, exhibiting low-pass behavior, small-amplitude motion tracking was band pass, with the best ocular movement gain occurring at ~0.8–1 Hz. When oblique directions were tested, we found that the horizontal component of pursuit gain was larger than the vertical component. Our results provide a catalog of the control abilities of the monkey oculomotor system for slow target motions, and they also support the notion that smooth fixational ocular drifts are controllable. This has implications for neural investigations of drift control and the image-motion consequences of drifts on visual coding in early visual areas. NEW & NOTEWORTHY We studied the efficacy of monkey smooth pursuit eye movements for very slow target velocities. Pursuit was impaired for sinusoidal motions of frequency less than ~0.8–1 Hz. Nonetheless, eye trajectory was still sinusoidally modulated, even at velocities lower than those observed during gaze fixation with slow ocular drifts. Our results characterize the slow control capabilities of the monkey oculomotor system and provide a basis for future understanding of the neural mechanisms for slow ocular drifts.

The world appears stable despite saccadic eye-movements. One possible explanation for this phenomenon is that the visual system predicts upcoming input across saccadic eye-movements based on peripheral preview of the saccadic target. We tested this idea using concurrent electroencephalography (EEG) and eye-tracking. Participants made cued saccades to peripheral upright or inverted face stimuli that changed orientation (invalid preview) or maintained orientation (valid preview) while the saccade was completed. Experiment 1 demonstrated better discrimination performance and a reduced fixation-locked N170 component (fN170) with valid than with invalid preview, demonstrating integration of pre- and post-saccadic information. Moreover, the early fixation-related potentials (FRP) showed a preview face inversion effect suggesting that some pre-saccadic input was represented in the brain until around 170 ms post fixation-onset. Experiment 2 replicated Experiment 1 and manipulated the proportion of valid and invalid trials to test whether the preview effect reflects context-based prediction across trials. A whole-scalp Bayes factor analysis showed that this manipulation did not alter the fN170 preview effect but did influence the face inversion effect before the saccade. The pre-saccadic inversion effect declined earlier in the mostly invalid block than in the mostly valid block, which is consistent with the notion of pre-saccadic expectations. In addition, in both studies, we found strong evidence for an interaction between the pre-saccadic preview stimulus and the post-saccadic target as early as 50 ms (Experiment 2) or 90 ms (Experiment 1) into the new fixation. These findings suggest that visual stability may involve three temporal stages: prediction about the saccadic target, integration of pre-saccadic and post-saccadic information at around 50-90 ms post fixation onset, and post-saccadic facilitation of rapid categorization.

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.

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.

As we look around the world, selecting our targets, competing events may occur at other locations. Depending on current goals, the viewer must decide whether to look at new events or to ignore them. Two experimental paradigms formalize these response options: double-step saccades and saccadic inhibition. In the first, the viewer must reorient to a newly appearing target; in the second, they must ignore it. Until now, the relationship between reorienting and inhibition has been unexplored. In three experiments, we found saccadic inhibition ∼100 msec after a new target onset, regardless of the task instruction. Moreover, if this automatic inhibition is boosted by an irrelevant flash, reorienting is facilitated, suggesting that saccadic inhibition plays a crucial role in visual behavior, as a bottom–up brake that buys the time needed for decisional processes to act. Saccadic inhibition may be a ubiquitous pause signal that provides the flexibility for voluntary behavior to emerge.

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.

It has long been known that eye movements are functionally involved in the generation and maintenance of mental images. Indeed, a number of studies demonstrated that voluntary eye movements interfere with mental imagery tasks (e.g., Laeng and Teodorescu in Cogn Sci 26:207-231, 2002). However, mental imagery is conceived as a multifarious cognitive function with at least two components, a spatial component and a visual component. The present study investigated the question of whether eye movements disrupt mental imagery in general or only its spatial component. We present data on healthy young adults, who performed visual and spatial imagery tasks concurrently with a smooth pursuit. In line with previous literature, results revealed that eye movements had a strong disruptive effect on spatial imagery. Moreover, we crucially demonstrated that eye movements had no disruptive effect when participants visualized the depictive aspects of an object. Therefore, we suggest that eye movements serve to a greater extent the spatial than the visual component of mental imagery.

Visual transient events during ongoing eye movement tasks inhibit saccades within a precise temporal window, spanning from around 60–120 ms after the event, having maximum effect at around 90 ms. It is not yet clear to what extent this saccadic inhibition phenomenon can be modulated by attention. We studied the saccadic inhibition induced by a bright flash above or below fixation, during the preparation of a saccade to a lateralized target, under two attentional manipulations. Experiment 1 demonstrated that exogenous precueing of a distractor's location reduced saccadic inhibition, consistent with inhibition of return. Experiment 2 manipulated the relative likelihood that a distractor would be presented above or below fixation. Saccadic inhibition magnitude was relatively reduced for distractors at the more likely location, implying that observers can endogenously suppress interference from specific locations within an oculomotor map. We discuss the implications of these results for models of saccade target selection in the superior colliculus.

Visual transients, such as a bright flash, reduce the proportion of saccades executed around 60-125 ms after flash onset, a phenomenon known as saccadic inhibition. Across three experiments, we apply a similar time-course analysis to the amplitudes and velocities of saccades. Alongside the expected reduction of saccade frequency in the key time period, we report two perturbations of the “main sequence”, one before and one after the period of saccadic inhibition. First, saccades launched between 30 to 70 ms following the flash were hypometric, with peak speed exceeding that expected for a saccade of similar amplitude. This finding was in contrast to the common idea that saccades have passed a “point-of-no-return” around 60 ms prior to launching, escaping interference from distractors. The early hypometric saccades observed were not a consequence of spatial averaging between target and distractor locations, as they were found not only following a localized central flash (Experiment 1), but also following a spatially generalized flash (Experiment 2). Second, across experiments, saccades launched at 110 ms post-flash, toward the end of saccadic inhibition, had normal amplitude but a peak speed higher than expected for that amplitude suggesting increased collicular excitation at the time of launching. Overall, the results show that saccades that escape inhibition following a visual transient are not necessarily unaffected, but instead can reveal interference in spatial and kinematic measures.

Distractors presented contralateral to a visual target inhibit the generation of saccades within a precise temporal window (Buonocore & McIntosh, 2008; Reingold & Stampe, 2002; Walker, Kentridge, & Findlay, 1995). The greatest ‘dip’ of saccadic inhibition typically occurs at about 90ms after distractor onset, with a subsequent recovery period showing an elevated frequency of saccades. It is not yet known how the spatial properties of the distractor stimulus influence the saccadic inhibition signature. To study this, we manipulated the size and the field of presentation of the distractor in four experiments. Experiment 1 demonstrated that the size of a distractor in the contralateral field is logarithmically related to the magnitude of the saccadic inhibition dip. This implies that the probability of a planned saccade being inhibited increases logarithmically with the size of the distractor. Experiment 2 showed a qualitatively similar but more pronounced effect of size for distractors in the ipsilateral field. Experiment 3 compared the effects of contralateral and ipsilateral distractors directly using a within-subjects design, confirming the more pronounced impact of ipsilateral distractors. Experiment 4 replicated the more pronounced effect of ipsilateral distractors in a task in which target side was unpredictable, confirming that the effect does not result merely from participants preparing in advance to ignore events on one side. We suggest that participants are more able to resist contralateral distraction during target selection, as they can more effectively withdraw attention from locations remote from the target than from locations close to it.

Whether mental visual images play a functional role in cognition or that propositional knowledge is sufficient for supporting performance in imagery tasks is a long-standing debate. It cannot be resolved using behavioural data alone, nor by brain imaging data alone; for example, across fMRI studies mental rotation has been shown to involve virtually all areas of the brain. Alternatively participants might adopt different cognitive strategies. We report behavioural and fMRI data for mental rotation from individuals reporting vivid or poor mental imagery. Groups differed in errors but not response times, and differed in brain activation patterns, suggesting that the groups performed the same task in different ways.

Previous repetitive Transcranial Magnetic Stimulation and neuroimaging studies showed that Broca's area is involved in the interaction between gestures and words. However, in these studies the nature of this interaction was not fully investigated; consequently, we addressed this issue in three behavioral experiments. When compared to the expression of one signal at a time, arm kinematics slowed down and voice parameters were amplified when congruent words plus gestures were simultaneously produced (experiment 1). When word and gesture were incongruent, arm kinematics did not change regardless of word category, whereas the gesture induced variation in vocal parameters of communicative and action words only (experiments 2 and 3). Data are discussed according to the hypothesis that integration between gesture and word occurs by transferring the social intention to interact directly with the interlocutor from the gesture to the word.

The remote distractor effect is a robust finding whereby a saccade to a lateralised visual target is delayed by the simultaneous, or near simultaneous, onset of a distractor in the opposite hemifield. Saccadic inhibition is a more recently discovered phenomenon whereby a transient change to the scene during a visual task induces a depression in saccadic frequency beginning within 70 ms, and maximal around 90-100 ms. We assessed whether saccadic inhibition is responsible for the increase in saccadic latency induced by remote distractors. Participants performed a simple saccadic task in which the delay between target and distractor was varied between 0, 25, 50, 100 and 150 ms. Examination of the distributions of saccadic latencies showed that each distractor produced a discrete dip in saccadic frequency, time-locked to distractor onset, conforming closely to the character of saccadic inhibition. We conclude that saccadic inhibition underlies the remote distractor effect.

The present study aimed to determine whether the representation of object affordances requires specification of the effector potentially interacting with the object: specifically, in this study, vision of the interacting hand. In Experiment 1 we used an apparatus by which a fruit to be reached and grasped was identified by word reading, whereas another (interfering) fruit was visually perceived at the same location as the target. The apparatus allowed visual presentation of the agent's interacting hand or prevented it. When visually presented, the hand was perceived as still at the start position even when it moved to grasp the fruit. An interference effect on the grasp congruent with the distractor size was observed only when the hand was visible. In Experiment 2, interference was observed also when a hand different from the agent's own was visually presented. In both Experiments 1 and 2 the visible fruit interfered with the arm's reach, but the effect was independent of its size and less dependent on the visually-presented hand. A control experiment (Experiment 3) enabled comparison of the interference of visual stimuli on targets identified by word reading (Experiments 1 and 2) with that of objects identified by word reading on visually-presented targets (Experiment 3). The interference induced by visual stimuli was stronger than the interference induced by objects identified by words (i.e. affordances evoked by visual stimuli were stronger than affordances evoked by semantics). Taken together, the results of the present study suggest that the specification of the agent's effector is necessary for the elicitation of affordances. However, the elicitation of these affordances was observed for interactions between object and hand (grasp), rather than for interactions between object and arm (reach). Finally, our data confirm the influence of semantics on the control of arm movements, though less strong than that due to visual input.

International audience; Remembering the past and imagining the future both rely on complex mental imagery. We considered the possibility that constructing a future scene might tap a component of mental imagery that is not as critical for remembering past scenes. Whereas visual imagery plays an important role in remembering the past, we predicted that spatial imagery plays a crucial role in imagining the future. For the purpose of teasing apart the different components underpinning scene construction in the two experiences of recalling episodic memories and shaping novel future events, we used a paradigm that might selectively affect one of these components (i.e., the spatial). Participants performed concurrent eye movements while remembering the past and imagining the future. These concurrent eye movements selectively interfere with spatial imagery, while sparing visual imagery. Eye movements prevented participants from imagining complex and detailed future scenes, but had no comparable effect on the recollection of past scenes. Similarities between remembering the past and imagining the future are coupled with some differences. The present findings uncover another fundamental divergence between the two processes.

Our perception of the surrounding environment remains stable despite the fact that we frequently change the retinal position of input by rapid gaze shifts (saccades). There is a long-standing debate whether visual stability depends on an active mechanism using an efference copy of the impending saccadic motor command. Behavioral studies showing changes in perception around the time of saccades are consistent with a predictive mechanism, but previous studies of perceptual effects in humans confounded saccade programming with the resulting physical eye movement. In three experiments, we used a saccadic inhibition (SI) paradigm to delay saccadic onset while participants were performing a perisaccadic localization task. As expected, the perceived position of the probe stimulus was systematically biased (compressed) toward the saccadic goal, already during the presaccadic interval. In the SI condition, the localization error was shifted in time, in line with it following saccade intention rather than execution. The pattern was not the consequence of the probe being captured by the timing of the flashed distractor, but depended instead on the delay in saccadic onset time caused by SI. Importantly, the same configurations of perceptual probes presented with a flashed backward mask when participants maintained fixation did not lead to similar localization errors as saccade trials. This pattern of results is consistent with an active, sensorimotor explanation for perisaccadic mislocalization and, more generally, theories emphasizing the role of motor prediction in visual stability.

We have suggested that the remote distractor effect (RDE), the elevation of average saccadic reaction time (SRT) induced by a task-irrelevant distractor, may be explained as a statistical consequence of a characteristic reshaping of the SRT distribution known as saccadic inhibition (SI; Buonocore & McIntosh, 2008). In a recent paper, Walker and Benson (2013) argue against this idea and claim that the RDE and SI are partly dissociable. Here, we examine this claim, taking the opportunity to clarify potential ambiguities about how SI affects average SRT, and how the presence of SI can be inferred from SRT distributions.We highlight what we consider to be the most interesting aspects of Walker and Benson’s data, and suggest that a more flexible and nuanced view of SI can account for them. In considering the relation between SI and the RDE, we conclude that the RDE may no longer be a useful concept for eye movement researchers.

The remote distractor effect (RDE) is a robust phenomenon whereby target-directed saccades are delayed by the appearance of a distractor. This effect persists even when the target location is perfectly predictable. The RDE has been studied extensively in the oculomotor domain but it is unknown whether it generalises to other spatially oriented responses. In three experiments, we tested whether the RDE generalises to manual aiming. Experiment 1 required participants to move their hand or eyes to predictable targets presented alone or accompanied by a distractor in the opposite hemifield. The RDE was observed for the eyes but not for the hand. Experiment 2 replicated this dissociation in a more naturalistic task in which eye movements were not constrained during manual aiming. Experiment 3 confirmed the lack of manual RDE across a wider range of distractor delays (0, 50, 100, and 150 ms). Our data imply that the RDE is specific to the oculomotor system, at least for non-foveal distractors. We suggest that the oculomotor RDE reflects competitive interactions between target and distractor representations in the superior colliculus, which are not necessarily shared by manual aiming.

Our peripheral vision is very limited. We can perceive isolated targets in our periphery, but when multiple stimuli are presented simultaneously our perception deteriorates drastically, a phenomenon known as crowding ([Whitney and Levi, 2011][1]). Crowded stimuli can still be detected, but can no