Biology subjects

Hafed, Z. M.

Publications and source records attributed to Hafed, Z. M..

At least 19 recordsLinked to original sources

bioRxiv2026

Sound unmasks short-latency tectal visual signals that are independent of the primary visual cortex

Optimal behavior requires active coordination between exogenous sensory events and internal brain states. Understanding such coordination is rendered challenging given the massive parallelism, followed by equally massive convergence, of sensory signals, even within a single sensory modality, when conveying information to the motor periphery. Here, using audiovisual stimulation and saccadic orienting, we show how multisensory stimulation differentially recruits visual processing pathways bypassing the primary visual cortex (V1), which may otherwise appear dormant. We reversibly inactivated primate V1 and explored the influences on short-latency reflexive saccadic resetting. Having recently shown that such resetting is eliminated by V1 inactivation, randomly interleaving task-irrelevant simultaneous sounds not only recovered the phenomenon, but it was also associated with V1-independent neuronal modulations in both the superior (SC) and inferior (IC) colliculi. These results show that even when the geniculostriate pathway is dominant, like in primates, alternative visual pathways still alter behavior under the right sensory contingencies.

neuroscience↗

bioRxiv2026

Much stronger coarse-to-fine visual processing in primate superior colliculus than primary visual cortex neurons

The visual system optimizes its signal processing properties to efficiently encode natural scenes. The superior colliculus (SC) and primary visual cortex (V1) both play important roles in visual-motor processing, and they both exhibit qualitatively similar visual responses. However, it is not clear whether the SC simply inherits V1s efficient coding image processing optimizations or not, especially given that the SC receives a substantial amount of direct anatomical inputs from V1. Here, by performing matched experiments in the two brain areas, as well as with the same visual stimuli and in the same experimental animals, we show that the dynamics of coarse-to-fine visual image processing in the SC are much stronger than those in V1. In the SC, visual response latencies, being fastest for coarse patterns, are dictated by image spatial frequency, independently of the spatial frequency tuning curves of the neurons. On the other hand, V1 visual response latencies are largely dominated by visual response sensitivity, which is itself much more broadband than in the SC. These observations remain fundamentally unchanged in active vision gaze-shift scenarios eliciting visual reafferent responses in both brain areas. Our results suggest that coarse-to-fine visual image processing dynamics are most observable, and thus most relevant, in visually-responsive neurons driving foveating eye movements, like in the SC. Besides explaining behavioral evidence for saccadic facilitation by images that are consistent with the statistics of natural scenes, these results indicate that coarse-to-fine visual processing dynamics are much more of a collicular than a cortical visual phenomenon.

neuroscience↗

bioRxiv2026

Further evidence of much higher covariation with saccadic reaction time of superior colliculus than primary visual cortex visual responses

Visual response strength in the primate superior colliculus (SC) has recently been shown to inversely correlate with trial-by-trial saccadic reaction time in a much stronger way than visual response strength in the primary visual cortex (V1). However, for any given visual stimulus onset, populations of neurons in each brain area are concurrently activated, leaving open the question of how V1 visual response strength can predict trial-by-trial saccadic reaction time when multiple simultaneously recorded neurons are taken into account. Using a classic visually-guided saccade task, here we assessed the quality of predicting trial-by-trial saccadic reaction time from the visual response strengths of 1 to 10 simultaneously recorded neurons in each brain area. For each session, we modeled saccadic reaction time as a weighted linear combination of the visual response strengths of N simultaneously recorded neurons. Consistent with the prior work, the visual response strength of a single SC neuron was better than that of a single V1 neuron at predicting reaction time. By adding more simultaneously recorded neurons, the prediction got much better in the SC, but not in V1. Only for 100% contrast dark stimuli (darker in luminance than the surrounding gray background) did V1 show an increase in prediction quality with more simultaneously recorded neurons. This increase, which was still substantially weaker than in the SC, could reflect the ecological relevance of dark contrasts in scenes. These results suggest that despite qualitative similarities between SC and V1 visual responses, SC visual responses are functionally reformatted from their V1 counterparts. SignificanceThe superior colliculus (SC) is an important sensory-motor structure for controlling eye movements, and it receives a significant portion of its inputs directly from the primary visual cortex (V1). Despite this, SC visual responses are much better correlated with trial-by-trial variability in saccadic eye movement timing than V1 visual responses, and this effect is strongly amplified when considering simultaneously recorded neurons. Thus, SC and V1 visual responses serve fundamentally different functions from a motor perspective.

neuroscience↗

bioRxiv2026

A transient signal in foveal superior colliculus neurons for jumpstarting peripheral saccadic orienting

The superior colliculus (SC) both senses the environment and orients gaze within it. While the SCs sensory and motor bursts appear qualitatively similar to each other, population activity structure in the two processing regimes (visual and motor) is very different, necessitating a hitherto unexplored rapid representational transformation, occurring on the scale of only tens of milliseconds. Here, we first show that when a planned saccade is released with a go signal, peripheral SC neurons representing the saccade target location exhibit a transient, short-latency pause right before their motor bursts eventually emerge. This pause starts within [~]50 ms from the go signal; it is stimulus-dependent; and it is significantly weaker in purely visual SC neurons than in saccade-related ones. Foveal SC neurons, on the other hand, transiently burst, and their bursts lead the peripheral neurons pauses by [~]10 milliseconds. These transient foveal bursts also lead the same foveal neurons saccade-related pauses, which are time-locked to movement generation. Remarkably, during immediate visually-guided saccade tasks, requiring a transformation from visual to motor peripheral bursts in <50-100 ms, the transient foveal SC bursts still occur, resulting in simultaneous short-latency bursting at two disparate SC loci: one foveal; and one eccentric and responding to the visual appearance of the saccade target. Our results suggest that in classic saccade tasks used to investigate visual, motor, and cognitive processes in primate brains, a transient foveal SC signal precedes peripheral saccadic orienting, and may facilitate a necessary rapid representational transformation needed for SC saccade motor bursts to ensue. SignificanceSaccade control studies often involve behavioral paradigms dissociating stimulus presentation, deliberation epochs, and "go" instructions. While the stimulus presentation, deliberation, and actual movement aspects have been well studied, the "go" phases of trials are less considered. We show that foveal superior colliculus neurons exhibit transient activity bursts at the "go" instruction for saccades, likely enabling a rapid representational transformations from a visual to a motor regime in the extrafoveal collicular neurons driving the eye movements.

neuroscience↗

bioRxiv2026

Transient focal inactivation of the primary visual cortex abolishes saccadic inhibition

Most organisms are perpetually engaged in an active-perception cycle: at any moment, planning, executing, or recovering from a given own movement. In the oculomotor system, such a cycle is under a powerful, reflexive, and short-latency interruptive influence by exogenous sensory stimulation, but the multitude of possible pathways eventually converging on the final oculomotor control gateway make it unknown how reflexive oculomotor inhibition takes place. Here we show that transient focal inactivation of the primary visual cortex abolishes visually-driven saccadic inhibition, suggesting an unequivocal dominance of the geniculostriate visual pathway over this robust behavioral reflex. Using chronic lesions, computational modeling, and fine-grained eye-movement analyses, we then show that latent visual signals bypassing the geniculostriate pathway are still present, but may not be as central as previously anticipated. These results recast classic views on visual-motor reflexes, and motivate functional and theoretical investigations of the multiplicity of parallel input-output loops in the brain.

neuroscience↗

bioRxiv2025

Vision dominates sound in mediating classic cue-induced microsaccadic eye movement modulations in rhesus macaque monkeys

Visual onsets in the environment cause a short-latency reduction in saccade generation likelihood. Concomitant with that, the metrics of the saccades that do happen near the time of saccadic inhibition reflect the landscape of stimulus-driven neural responses in topographically organized brain maps. While certain aspects of saccadic inhibition have already been explored from a neurophysiological perspective, several questions remain, including which sensory-motor pathways propagate visual input information to the final oculomotor control circuitry with such short latencies. Here, motivated by evidence of a dissociation between temporal and spatial aspects of saccadic inhibition, we devised behavioral paradigms experimentally manipulating either aspect. Rhesus macaque monkeys maintained gaze fixation, and we characterized visually-driven microsaccadic inhibition with and without paired auditory pulses. In one condition, the sound pulses were spatially-nonlateralized, thus only affecting the temporal processes associated with microsaccadic inhibition; in another, the pulses were spatially-lateralized, affecting both the temporal and spatial components. We found that sound pulses alone barely affected microsaccade rates. However, when paired with visual stimuli, they accelerated the timing of visually-driven microsaccadic inhibition by [~]14-18 ms. In terms of microsaccade directions, spatially-nonlateralized sounds interfered with, but did not eliminate, visually-driven direction modulations. Surprisingly, lateralized sounds had a much weaker effect on microsaccade direction modulations, even when the sound source was in the opposite hemifield as the appearing visual stimulus. We conclude that vision dominates sound in mediating classic microsaccadic inhibition, and we argue that our paradigms are ideal for neurophysiological investigations of the parallel sensory-motor pathways contributing to such inhibition. SignificanceCoordination of internal oculomotor eye movement plans with exogenous sensory events entails rapid inhibition of the saccadic eye movement system, but the pathways mediating the inhibition are unknown. We devised novel behavioral paradigms in primates, involving multisensory stimulation, which allow neurophysiological experiments to isolate the contributions of individual sensory, motor, and sensory-motor brain areas to saccadic inhibition. Such paradigms underscore that inhibition involves distinct temporal and spatial processes that are dominated by the visual modality.

neuroscience↗

bioRxiv2025

Much higher covariation with foveation timing by superior colliculus than primary visual cortical neuronal activity

The superior colliculus (SC) is a potent driver for orienting movements, but it also possesses short-latency visual responses. Even though such responses largely derive from direct primary visual cortical (V1) input, their relationship to V1 activity has never been analyzed with the same experimental subjects and stimuli. Here, we revisited pioneering observations that trial-by-trial variability in either SC or V1 visual responses may predict eye movement timing variability. We found that V1 covariation with behavioral variability was virtually non-existent in comparison to the SC, whether with respect to visual response onset latency, visual response strength, or pre-stimulus state. By far, our largest predictor of behavioral variability was visual response strength in SC visual-motor neurons. These results suggest that the SC reformats its sensory inputs for exploitation of the SCs proximity to the motor periphery; V1 aids in jumpstarting the sensing process, but the SC much more directly supports visually-driven orienting.

neuroscience↗

bioRxiv2025

Species-specific oculomotor control tolerances predict saccadic suppression strength in macaques and zebrafish

Active sensing necessarily requires integrating information about both self-generated movements as well as past, present, and future afferent inputs. However, such information is inherently variable and relies, at least in part, on uncertain extrapolations. Here, using saccadic suppression of visual sensitivity as a classic example of sensory-motor integration, we show that suppression strength in two drastically different species, macaque monkeys and zebrafish larvae, may be a direct outcome of efficient state estimation in the presence of uncontrollable sensory and motor variability. Bayesian estimator models suggest that optimal saccadic suppression should rely not just on the sensory-motor information being processed, but also on the time-dependent magnitude of unexplained variability in the nervous system encoding it. In both macaques and zebrafish larvae, and using matching visual stimulation regimes optimized for each species receptive field properties, we experimentally measured saccadic suppression strength in the superior colliculus (SC) of the monkeys and the homologous optic tectum (OT) of the fish. We also experimentally quantified additive and multiplicative motor noise components in the oculomotor behavior of both species, and we furthermore estimated noise in the sensory systems. We found that inter-species differences in sensory and motor noise levels and their theoretically predicted impacts on visual sensitivity are consistent with our experimentally observed differences in saccadic suppression strength between the fish and the monkeys. Because sensory and motor noise levels can reflect the amounts of available neural resources committed to a given task, our results strongly underscore the value of incorporating computational resource limits into investigating performance differences that have evolved in homologous brain areas.

neuroscience↗

bioRxiv2025

Signaling of trans-saccadic prediction error by foveal neurons of the monkey superior colliculus

Across saccades, neurons in retinotopically organized visual representations experience drastically different images, but visual percepts remain stable. Here we investigated whether such stability can be mediated, in part, via prediction-error signaling by neurons processing post-saccadic visual images. We specifically recorded from foveal superior colliculus (SC) neurons when a visual image only overlapped with their response fields (RFs) after foveating saccades but not pre-saccadically. When we rapidly changed the target features intra-saccadically, the foveal neurons post-saccadic visual reafferent responses were elevated, even though the neurons did not directly sample the pre-saccadic extrafoveal target features. This effect did not occur in the absence of saccades, and it also scaled with the extent of the introduced intra-saccadic image feature discrepancies. These results suggest that foveal SC neurons may signal a trans-saccadic prediction error when the foveated image stimulating them is inconsistent with that expected from pre-saccadic extrafoveal representations, a potential perceptual stability mechanism.

neuroscience↗

bioRxiv2025

Saccadic Suppression Enhances Saliency of Prey-Like Stimuli in the Optic Tectum

Saccadic suppression, a reduction in visual sensitivity around the time of rapid eye movements, is well-documented in primate psychophysics but its mechanisms and functions remain debated. Here, we use zebrafish to trace the origins of saccadic suppression and we demonstrate how saccadic suppression selectively enhances the visual salience of ecologically relevant stimuli. Saccadic suppression thus contributes to more than just compensation for rapid saccade-induced image shifts. We first established a behavioral correlate of saccadic suppression in larval zebrafish escape behavior. Then, using electrophysiology, we show that retinal ganglion cells jumpstart saccadic suppression in a spatial frequency dependent manner. Calcium imaging, combined with 360{degrees} visual stimulation and behavioral tracking, revealed that motor signals enhance peri-saccadic suppression strength in the optic tectum, where suppression lasts for more than 3000 ms. Notably, saccadic suppression is much weaker and more short-lived for stimuli related to hunting or escape behavior than for behaviorally less relevant global flashes. This unequal attenuation effectively increases the salience of the ecologically relevant stimuli in the optic tectum after saccades. Our results demonstrate that saccadic suppression integrates visual and motor signals to optimize sensory processing within neural constraints, and they provide insights into evolutionarily conserved visual strategies.

neuroscience↗

bioRxiv2024

Foveal action for the control of extrafoveal vision

Microsaccades have been convincingly linked to extrafoveal covert attention shifts for more than two decades. However, the direction of causality between individual microsaccade generation and an alteration in both extrafoveal visual sensitivity and behavior remains debated: do microsaccades merely reflect, perhaps probabilistically, an altered extrafoveal sensitivity, or is the act of generating microsaccades sufficient, on its own, to modify such sensitivity? Using a novel exploitation of real-time retinal image stabilization, behavior, and neurophysiology in the superior colliculus of rhesus macaque monkeys, we show that exclusive experimental control over foveal oculomotor state is entirely sufficient to influence extrafoveal sensitivity. This happens for eccentricities as large as [~]50 times those associated with microsaccades, and it also takes place in the absence of any differential attentional demands. Most importantly, such influence is mediated through well-known, classic pre- and post-saccadic visual processing changes. Thus, seemingly-innocuous subliminal eye movements do constitute an integral component of cognitive processes like attention.

neuroscience↗

bioRxiv2024

Two-dimensional perisaccadic visual mislocalization in rhesus macaque monkeys

Perceptual localization of brief, high contrast perisaccadic visual probes is grossly erroneous. While this phenomenon has been extensively studied in humans, more needs to be learned about its underlying neural mechanisms. This ideally requires running similar behavioral paradigms in animals. However, during neurophysiology, neurons encountered in the relevant sensory and sensory-motor brain areas for visual mislocalization can have arbitrary, non-cardinal response field locations. This necessitates using mislocalization paradigms that can work with any saccade direction. Here, we first established such a paradigm in three male rhesus macaque monkeys. In every trial, the monkeys generated a visually-guided saccade towards an eccentric target. Once a saccade onset was detected, we presented a brief flash at one of three possible locations ahead of the saccade target location. After an experimentally-imposed delay period, we removed the saccade target, and the monkeys were then required to generate a memory-guided saccade towards the remembered flash location. All three monkeys readily learned the task, and, like humans, they all showed strong backward mislocalization towards the saccade target, which recovered for later flashes from the saccade time. Importantly, we then replicated a well-known property of human perisaccadic mislocalization, as revealed by two-dimensional mislocalization paradigms: that mislocalization is strongest for upward saccades. For horizontal saccades, we additionally found stronger mislocalization for upper visual field flashes, again consistent with humans. Our results establish a robust two-dimensional mislocalization paradigm in monkeys, and they pave the way for exploring the neural mechanisms underlying the dependence of perisaccadic mislocalization strength on saccade direction. Significance statementVisual perception is strongly altered around the time of saccades. Such alteration is often studied by characterizing how brief perisaccadic visual flashes are perceptually localized. While the properties of visual mislocalization have been exhaustively studied, the underlying neural mechanisms remain elusive, and this is due to a lack of suitable behavioral paradigms in animal models. We describe such a paradigm for macaques, which are ideal for exploring sensory-motor neural processes related to perisaccadic mislocalization.

neuroscience↗

bioRxiv2024

Superior colliculus peri-saccadic field potentials are dominated by a visual sensory preference for the upper visual field

The primate superior colliculus (SC) plays important sensory, cognitive, and motor processing roles. Among its properties, the SC has clear visual field asymmetries: visual responses are stronger in the upper visual field representation, whereas saccade-related motor bursts are weaker. Here, I asked whether peri-saccadic SC network activity can still reflect the SCs visual sensitivity asymmetry, thus supporting recent evidence of sensory-related signals embedded within the SCs motor bursts. I analyzed collicular peri-saccadic local field potential (LFP) modulations and found them to be much stronger in the upper visual field, despite the weaker motor bursts. This effect persisted even with saccades towards a blank, suggesting an importance of visual field location. I also found that engaging working memory during saccade preparation differentially modulated the SCs LFPs, again with a dichotomous upper/lower visual field asymmetry. I conclude that the SC network possesses a clear sensory signal at the time of saccade generation.

neuroscience↗

bioRxiv2024

Stronger premicrosaccadic sensitivity enhancement for dark contrasts in the primate superior colliculus

Microsaccades are associated with enhanced visual perception and neural sensitivity right before their onset, and this has implications for interpreting experiments involving the covert allocation of peripheral spatial attention. However, the detailed properties of premicrosaccadic enhancement are not fully known. Here we investigated how such enhancement in the superior colliculus depends on luminance polarity. Rhesus macaque monkeys fixated a small spot while we presented either dark or bright image patches of different contrasts within the recorded neurons response fields. Besides replicating premicrosaccadic enhancement of visual sensitivity, we observed stronger enhancement for dark contrasts. This was especially true at moderate contrast levels (such as 10-20%), and it occurred independent of an individual neurons preference for either darks or brights. On the other hand, postmicrosaccadic visual sensitivity suppression was similar for either luminance polarity. Our results reveal an intriguing asymmetry in the properties of perimicrosaccadic modulations of superior colliculus visual neural sensitivity.

neuroscience↗

bioRxiv2024

Perisaccadic perceptual mislocalization strength depends on the visual appearance of saccade targets

We normally perceive a stable visual environment despite repetitive eye movements. To achieve such stability, visual processing integrates information across saccades, and laboratory hallmarks of such integration are robustly observed by presenting brief perimovement visual probes. In one classic phenomenon, perceived probe locations are grossly erroneous. This phenomenon is believed to depend, at least in part, on corollary discharge associated with saccade-related neuronal movement commands. However, we recently found that superior colliculus motor bursts, a known source of corollary discharge, can be different for different image appearances of the saccade target. Therefore, here we investigated whether perisaccadic perceptual mislocalization also depends on saccade-target appearance. We asked human participants to generate saccades to either low (0.5 cycles/deg) or high (5 cycles/deg) spatial frequency gratings. We always placed a high contrast target spot at grating center, to ensure matched saccades across image types. We presented brief perisaccadic probes, which were high in contrast to avoid saccadic suppression, and the subjects pointed (via mouse cursor) at their perceived locations. We observed stronger perisaccadic mislocalization for low spatial frequency saccade targets, and for upper visual field probe locations. This was despite matched saccade metrics and kinematics across conditions, and it was also despite matched probe visibility for the different saccade target images (low versus high spatial frequency gratings). To the extent that perisaccadic perceptual mislocalization depends on corollary discharge, our results suggest that such discharge might relay more than just spatial saccade vectors to the visual system; saccade-target visual features can also be transmitted. SignificanceBrief visual probes are grossly mislocalized when presented in the temporal vicinity of saccades. While the mechanisms of such mislocalization are still under investigation, one component of them could derive from corollary discharge signals associated with saccade movement commands. Here, we were motivated by the observation that superior colliculus movement bursts, one source of corollary discharge, vary with saccade-target image appearance. If so, then perisaccadic mislocalization should also do so, which we confirmed.

neuroscience↗

bioRxiv2024

Microsaccadic suppression of peripheral perceptual detection performance as a function of foveated visual image appearance

Microsaccades are known to be associated with a deficit in perceptual detection performance for brief probe flashes presented in their temporal vicinity. However, it is still not clear how such a deficit might depend on the visual environment across which microsaccades are generated. Here, and motivated by studies demonstrating an interaction between visual background image appearance and perceptual suppression strength associated with large saccades, we probed peripheral perceptual detection performance of human subjects while they generated microsaccades over three different visual backgrounds. Subjects fixated near the center of a low spatial frequency grating, a high spatial frequency grating, or a small white fixation spot over an otherwise gray background. When a computer process detected a microsaccade, it presented a brief peripheral probe flash at one of four locations (over a uniform gray background), and at different times. After collecting full psychometric curves, we found that both perceptual detection thresholds and slopes of psychometric curves were impaired for peripheral flashes in the immediate temporal vicinity of microsaccades, and they recovered with later flash times. Importantly, the threshold elevations, but not the psychometric slope reductions, were stronger for the white fixation spot than for either of the two gratings. Thus, like with larger saccades, microsaccadic suppression strength can show a certain degree of image-dependence. However, unlike with larger saccades, stronger microsaccadic suppression did not occur with low spatial frequency textures. This observation might reflect the different spatio-temporal retinal transients associated with the small microsaccades in our study versus larger saccades.

neuroscience↗

bioRxiv2023

Visual feature tuning properties of short-latency stimulus-driven ocular position drift responses during gaze fixation

Ocular position drifts during gaze fixation are generally considered to be random walks. However, we recently identified a short-latency ocular position drift response, of approximately 1 min arc amplitude, that is triggered within <100 ms by visual onsets. This systematic eye movement response is feature-tuned and seems to be coordinated with a simultaneous resetting of the saccadic system by visual stimuli. However, much remains to be learned about the drift response, especially for designing better-informed neurophysiological experiments unraveling its mechanistic substrates. Here we systematically tested multiple new feature tuning properties of drift responses. Using highly precise eye tracking in three male rhesus macaque monkeys, we found that drift responses still occur for tiny foveal visual stimuli. Moreover, the responses exhibit size tuning, scaling their amplitude as a function of stimulus size, and they also possess a monotonically increasing contrast sensitivity curve. Importantly, short-latency drift responses still occur for small peripheral visual targets, which additionally introduce spatially-directed modulations in drift trajectories towards the appearing peripheral stimuli. Drift responses also remain predominantly upward even for stimuli exclusively located in the lower visual field, and even when starting gaze position is upward. When we checked the timing of drift responses, we found that it was better synchronized to stimulus-induced saccadic inhibition timing than to stimulus onset. These results, along with a suppression of drift response amplitudes by peri-stimulus saccades, suggest that drift responses reflect the rapid impacts of short-latency and feature-tuned visual neural activity on final oculomotor control circuitry in the brain. SignificanceDuring gaze fixation, the eye drifts slowly in between microsaccades. While eye position drifts are generally considered to be random eye movements, we recently found that they are modulated with very short latencies by some stimulus onsets. Here we characterized the feature-tuning properties of such stimulus-driven drift responses. Our results demonstrate that drift eye movements are not random, and that visual stimuli can impact them in a manner similar to how such stimuli impact microsaccades.

neuroscience↗

bioRxiv2023

Visual feature tuning properties of stimulus-driven saccadic inhibition in macaque monkeys

Saccadic inhibition refers to a short-latency transient cessation of saccade generation after visual sensory transients. This oculomotor phenomenon occurs with a latency that is consistent with a rapid influence of sensory responses, such as stimulus-induced visual bursts, on oculomotor control circuitry. However, the neural mechanisms underlying saccadic inhibition are not well understood. Here, we exploited the fact that macaque monkeys experience robust saccadic inhibition to test the hypothesis that inhibition time and strength exhibit systematic visual feature tuning properties to a multitude of visual feature dimensions commonly used in vision science. We measured saccades in three monkeys actively controlling their gaze on a target, and we presented visual onset events at random times. Across six experiments, the visual onsets tested size, spatial frequency, contrast, motion direction, and motion speed dependencies of saccadic inhibition. We also investigated how inhibition might depend on the behavioral relevance of the appearing stimuli. We found that saccadic inhibition starts earlier, and is stronger, for large stimuli of low spatial frequencies and high contrasts. Moreover, saccadic inhibition timing depends on motion direction, with earlier inhibition systematically occurring for horizontally than for vertically drifting gratings. On the other hand, saccadic inhibition is stronger for faster motions, and when the appearing stimuli are subsequently foveated. Besides documenting a range of feature tuning dimensions of saccadic inhibition on the properties of exogenous visual stimuli, our results establish macaque monkeys as an ideal model system for unraveling the neural mechanisms underlying a highly ubiquitous oculomotor phenomenon in visual neuroscience. New and noteworthyVisual onsets dramatically reduce saccade generation likelihood with very short latencies. Such latencies suggest that stimulus-induced visual responses, normally jumpstarting perceptual and scene analysis processes, can also directly impact the decision of whether to generate saccades or not, causing saccadic inhibition. Consistent with this, we found that changing the appearance of the visual onsets systematically alters the properties of saccadic inhibition. These results constrain neurally-inspired models of coordination between saccade generation and exogenous sensory stimulation.

neuroscience↗