Biology subjects

Buonocore, A.

Publications and source records attributed to Buonocore, A..

17 recordsLinked to original sources

bioRxiv2026

Mapping memory-guided saccade population receptive fields reveals principles of cortical organization along the human intraparietal sulcus

The intraparietal sulcus is a central hub for motor planning and sensorimotor integration. Its responses are known to support coordinate transformations across reference frames and modalities--for example, eye-position gain fields that convert retinotopic, fovea-centred signals into head-centred representations. In the oculomotor domain, the human intraparietal sulcus is sensitive to eye-movement planning and has been extensively studied using memory-guided saccade paradigms. These classic approaches have revealed topographic organization and contralateral sensitivity for preferred direction in saccade planning and execution. However, such designs provide detailed information about preferred direction; they do not probe tuning width: how narrowly or broadly a given cortical location responds around its preferred direction. At present, it remains unclear whether and how tuning width is organized along the human intraparietal sulcus. Critically, neurophysiological studies in non-human primates do not offer systematic and extensive measurements of tuning width. Moreover, the relationship between tuning width and preferred direction at the population level in human intraparietal cortex is unknown. Here, we address these questions using a forward-modelling approach combined with high-field (7-Tesla) functional MRI. We observe contralateral preference for preferred direction in saccade planning and execution, as well as a novel large-scale organization of preferred saccade tuning width, in vivo, in humans. Highlightssaccade planning and execution tuning width is arranged topographically along human early visual cortex and human intraparietal sulcus; specificity of voxel-level saccade planning and execution decreases along the visual hierarchy; specificity of population-level saccade planning and execution increases along the visual hierarchy; forward modelling applied to memory-guided saccade paradigm outperforms the standard phase-encoding approach;

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bioRxiv2025

Sustained dynamics of saccadic inhibition and adaptive oculomotor responses during continuous exploration

In natural environments, stimuli often recur across time and space, requiring the visual system to remain sensitive to novelty while managing predictability. A central question in systems neuroscience is how motor systems adapt to repeated sensory events without compromising responsiveness. We investigated this adaptive capacity using saccadic inhibition (SI)--a reflexive suppression of eye movements triggered by sudden visual transients--as a probe of oculomotor dynamics during naturalistic viewing. Human participants (N = 21) freely explored visual arrays while brief gaze-contingent flashes appeared five times at random intervals, either foveally or parafoveally. SI reliably occurred [~]120 ms post-flash across repetitions and locations, indicating robust sensory-driven inhibition. However, the rebound phase--reflecting saccade reprogramming--showed a progressive decline. In a second experiment (N = 19), only the first or the fifth flash was visible on each trial. In this case, neither inhibition nor rebound was altered, suggesting that the rebound decline is driven by repeated sensory stimulation rather than exploration time. This dissociation reveals selective habituation of motor re-engagement mechanisms, while reflexive inhibitory gating remains stable. We propose that inhibition is mediated by circuitry that transiently suppresses saccade initiation and resists habituation. By contrast, the weakening rebound reflects a separate, habituation-prone route that reduces saccade generation to irrelevant events. Functionally, this imbalance implies a recalibration within the saccade generator, preserving inhibitory capacity while constraining motor output. Our findings uncover a distinct form of oculomotor habituation and demonstrate how SI reveals dynamic decoupling of sensory input and motor output under repeated stimulation. Significance StatementThe ability to interrupt and resume eye movements in response to environmental changes is fundamental to visual exploration. We investigated how this process unfolds across repeated visual transients in naturalistic conditions. Our findings show that saccadic inhibition remains stable across time, whereas the subsequent rebound phase habituates. This dissociation suggests that distinct processes mediate reflexive interruption and motor recovery habituation. Our data indicate that dynamic modulation of motor gating circuits is a mechanism for optimizing oculomotor behavior. These results deepen our understanding of visual-motor coordination, provide insight about the constraints governing the underlying system circuitry, and may inform clinical tools for assessing sensorimotor adaptability in health and disease.

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bioRxiv2025

Visual performance fields during Saccadic Suppression of Image Displacement

Visual perception is not homogeneous throughout the visual field. Performance is generally better along the horizontal meridian compared to the vertical meridian, and in the lower compared to the upper visual field. These asymmetries in visual performance are reflected in structural asymmetries in early visual cortex. When exploring a visual scene, eye movements occur continuously, with visual perception resulting from a tight interplay between the visual as well as the oculomotor systems. Literature on visual performance across visual fields during saccades is limited, but existing studies show that perceptual performance during saccades is indistinguishable between the upper and the lower visual fields, or altogether better in the upper visual field compared to lower. In the current exploratory study, we asked participants to detect the direction of target displacement across visual fields, while performing a saccade as well as at fixation. During fixation and saccade viewing conditions, performance on the task was better along the horizontal compared to the vertical meridian. However, we did not observe a robust difference in performance between the lower and upper visual field, neither at fixation nor when participants were requested to perform saccades. We interpret our results based on known behavioural and neural anisotropies, as well as considering evolutionary approaches to the perception-action cycle.

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bioRxiv2025

The Influence of Spatial Frequencies, Orientation and Familiarity on Face Stimuli Integration

When we observe an object, our visual system identifies its shape and integrates it with specific details to form a coherent representation. This coarse-to-fine approach involves rapid processing of low spatial frequency (LSF) content to generate a basic template, which aids the integration of the more detailed high spatial frequency (HSF) information. Here we explore with two experiments how the contribution of LSF and HSF integration extends to face processing. To do so, we leveraged the face inversion effect, whereby inverted faces are more difficult to recognize than upright ones. In Experiment 1, ten participants matched two familiar faces displayed in rapid succession (template and probe face, respectively). The template and the probe shared either the same SF (congruent) or had complementary SF (incongruent). In congruent conditions, HSF templates yielded better matching accuracy than LSF templates. However, in incongruent conditions, mapping LSF probes onto HSF templates was more effective, but only for upright faces. We propose that, depending on the task, holistic processing may be facilitated by detailed information. In Experiment 2, twelve participants performed the same task with both familiar and unfamiliar faces. While for familiar faces the effects were the same as Experiment 1, for unfamiliar faces the overall accuracy was better for congruent than incongruent conditions, and, crucially, it was independent of the template SF. Our results challenge the view that LSF content provides a foundational template for integrating HSF information, and instead suggest a flexible encoding of SF information, that depends on image contingencies.

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bioRxiv2024

Contributions of temporal and spatial masking signals in perception of sequential visual events

Accurate perception of time and space is essential for moment-to-moment interactions with our surroundings. This process requires flexibility, as it integrates information from our actions and the external context. Probing the visual system during the updating process reveals spatiotemporal distortions, where sequential stimuli appear closer in time and space than they are. These effects occur perisaccadically or when a visual mask follows the stimuli. The study investigated whether non-overlapping visual masks could influence temporal inversion judgments (TOJs), suggesting that a temporal signal might act as an anchor during updating. In Experiment 1, participants judged the temporal order of two stimuli under three conditions: no mask, a full-field mask, or a partial mask avoiding stimulis locations. Compared to no mask, both masks triggered TOJs when presented within 30 milliseconds of the second stimulus. In a control experiment, delaying mask onset by 30 milliseconds eliminated the inversion effect. In Experiment 2, TOJs were observed for both ipsilateral and contralateral masks, suggesting that long range inhibitory signals might also contribute to the effect. Together, these findings indicate that temporal inversions can occur with non-overlapping stimuli masks configuration, pointing to a non-spatial signal related to mask timing as the underlying mechanism.

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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.

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bioRxiv2022

Peri-saccadic visual sensitivity is higher in the upper visual field

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 fields, we asked whether peri-saccadic orientation identification performance is dominated by one or the other spatial anisotropy. Humans (48 participants, 29 females) reported the orientation of peri-saccadic upper visual field stimuli significantly better than lower visual field stimuli, unlike their performance during steady-state gaze fixation, and contrary to expected perceptual superiority in the lower visual field in the absence of saccades. Consistent with this, peri-saccadic superior colliculus visual neural responses in two male rhesus macaque monkeys were also significantly stronger in the upper visual field than in the lower visual field. Thus, peri-saccadic orientation identification performance is more in line with oculomotor, rather than visual, map spatial anisotropies. Significance statementDifferent brain areas respond to visual stimulation, but they differ in the degrees of functional specializations and spatial anisotropies that they exhibit. For example, the superior colliculus both responds to visual stimulation, like the primary visual cortex, and controls oculomotor behavior. Compared to the primary visual cortex, the superior colliculus exhibits an opposite pattern of upper/lower visual field anisotropy, being more sensitive to the upper visual field. Here, we show that human peri-saccadic orientation identification performance is better in the upper compared to the lower visual field. Consistent with this, monkey superior colliculus visual neural responses to peri-saccadic stimuli follow a similar pattern. Our results indicate that peri-saccadic perceptual performance reflects oculomotor, rather than visual, map spatial anisotropies.

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bioRxiv2020

Time-locked inhibition of covert orienting

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.

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bioRxiv2020

Task-irrelevant visual forms facilitate covert and overt spatial selection

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.

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bioRxiv2020

Instantaneous movement-unrelated midbrain activity modifies ongoing eye movements

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.

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bioRxiv2020

Dependence of the stimulus-driven microsaccade rate signature on visual stimulus polarity

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.

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bioRxiv2020

Rapid stimulus-driven modulation of slow ocular position drifts

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.

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bioRxiv2019

Post-saccadic face processing is modulated by pre-saccadic preview: Evidence from fixation-related potentials

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.\n\nSignificance 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.

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bioRxiv2019

Memory-guided microsaccades

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 exhibited 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.

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bioRxiv2018

Previewing a face in the periphery reduces the fN170: Combined EEG and eye-tracking suggests two stages of trans-saccadic predictive processes

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 could change (invalid preview) or keep their orientation (valid preview) across the saccade. Experiment 1 demonstrated better discrimination performance and a reduced fixation-locked N170 (fN170) with valid than with invalid preview demonstrating integration of pre- and post-saccadic information. Moreover, the early fixation-locked EEG showed a preview face inversion effect suggesting that we perceive pre-saccadic input up to about 170 ms post fixation-onset, at least for face orientation. Experiment 2 replicated Experiment 1 and manipulated the proportion of valid and invalid trials (mostly valid versus mostly invalid, 66.6% to 33.3%) to test whether the preview effect reflected active expectations. A whole-scalp Bayes factor analysis provided evidence for no influence of proportion on the fN170 preview effect. Instead, before the saccade the preview face orientation effect declined earlier in the mostly invalid than in the mostly valid block suggesting some form of pre-saccadic expectations. We conclude that visual stability is achieved by two trans-saccadic integration processes: pre-saccadic prediction, reflected in the pre-saccadic proportion modulation, and early post-saccadic change-detection reflected in the fN170 preview effect.

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bioRxiv2018

Eye-position error influence over \"open-loop\" smooth pursuit initiation

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 runs directly 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 we 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 backwards errors reducing it. Catch-up saccade frequencies and amplitudes were also similarly altered [~]50 ms after transient signals, much like 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.

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bioRxiv2018

The transfer function of the rhesus macaque oculomotor system for small-amplitude slow motion trajectories

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 directions. Maximum target displacement in the motion trajectory was 30 min arc (0.5 deg), 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, like 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 catalogue 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.

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