Biology subjects

Coop, S. H.

Publications and source records attributed to Coop, S. H..

4 recordsLinked to original sources

bioRxiv2026

Neural subpopulations in marmoset area MT/MTC detect and discount saccade-related retinal motion

Primates rely on eye movements made 2-3 times every second to scan their visual environment. Each eye movement induces substantial retinal motion, yet observers readily suppress it to stitch together the percept of a stable world. Neurons in the middle temporal (MT) and medial superior temporal (MST) areas respond to motion, but also suppress that response during eye movements (Bremmer et al., 2009; Leopold & Logothetis, 1998; Thiele et al., 2002). This saccadic suppression could reflect the influence of corollary feedback from eye movement related brain structures (Berman et al., 2017). However, visual signals that detect wide-field motion characteristic of a saccade could also contribute to suppression, akin to visual masking (Idrees et al., 2020). We sought to disentangle the relative contributions of visual signals and corollary discharge in driving saccadic suppression in areas MT and MTC in marmoset monkeys. Marmosets freely viewed natural images, blank backgrounds, or externally moving images that simulated saccades, and also made saccades in complete darkness. We found a diversity of saccadic modulation across the population. Some neurons showed short latency excitatory responses to saccades while others showed suppression. Still others showed a bi-phasic response that began with suppression followed by an excitatory rebound. Neurons with early responses were frequently tuned for the direction of saccades on natural images and retained that same tuning for saccades on blank screens or in complete darkness, thus supporting a role for corollary feedback. However, these neurons also responded with similar directional tuning for retinal motion created by simulating saccades while the eyes were fixed, and thus also appear to integrate visual cues for saccadic motion. More so, these units were biased towards having narrow spike waveforms consistent with putative inhibitory cells, which drive suppression observed in the rest of the population. We also found a subset of neurons that responded robustly to simulated saccadic motion but had negligible response to motion from real saccades, such that they discounted saccade induced motion. Those neurons were biased to have broader spike waveforms, consistent with being putative excitatory projection neurons and could support our percept of stability during eye movements.

neuroscience↗

bioRxiv2022

Pre-saccadic neural enhancements in marmoset area MT mimic covert attention

Each time we make an eye movement, attention moves before the eyes, resulting in a perceptual enhancement at the target. Recent psychophysical studies suggest that this pre-saccadic attention enhances the visual features at the saccade target, whereas covert attention causes only spatially-selective enhancements. While previous non-human primate studies have found that pre-saccadic attention does enhance neural responses spatially, no studies have tested if changes in neural tuning reflects an automatic feature enhancement. Here we examined pre-saccadic attention using a saccade foraging task developed for marmoset monkeys. We recorded from neurons in the middle temporal (MT) area with peripheral receptive fields that contained a motion stimulus which would either be the target of a saccade or a distracter as a saccade was made to another location. We established that marmosets, like macaques, show enhanced pre-saccadic neural responses for saccades towards the receptive field, including increases in firing rate and motion information. We then examined if the specific changes in neural tuning might support feature enhancements for the target. Neurons exhibited diverse changes in tuning, but predominantly showed additive and multiplicative increases that were uniformly applied across motion directions. These findings confirm that marmoset monkeys, like macaques, exhibit pre-saccadic neural enhancements during saccade foraging tasks with minimal training requirements. However, at the level of individual neurons, the lack of feature-tuned enhancements is similar to neural effects reported during covert spatial attention. Significance StatementAttention leads eye movements producing perceptual enhancements at saccade targets. Recent psychophysical studies indicate that increases in pre-saccadic sensitivity are concentrated around features of the target. We tested at the neural level how pre-saccadic attention modulates the tuning curves of visual neurons in area MT of marmoset monkeys. While neurons exhibited clear pre-saccadic enhancements that were consistent with previous studies in macaques, the changes in tuning were uniform across tuning. These results show pre-saccadic enhancements are a general feature of visual processing, shared by New World monkeys, but at the level of individual neurons enhancements are uniform across features much like what has been reported previously for covert attention.

neuroscience↗

bioRxiv2022

Post-saccadic following in the marmoset monkey as a read-out of pre-saccadic attention

Primates move their eyes 2-3 times per second to bring objects of interest to central, high-resolution vision. For moving objects, they use a combination of rapid saccadic eye movements along with smooth following movements to track targets continuously. Each saccadic eye movement produces perceptual enhancements for the target. And for saccades that are made to moving targets, or stationary apertures that contain motion, there is a smooth post-saccadic following response (PFR) of the target motion (Kwon et al, 2019). This PFR occurs involuntarily even when the motion is task irrelevant and could provide an automatic behavioral read-out of the targets motion. However, PFR movements are small, so it is unclear how reliable they would be as a trial-by-trial read-out. Here we examined PFR in marmoset monkeys performing a foraging task that requires almost no training and which has been shown to involve pre-saccadic neural enhancements of motion selective responses in visual area MT (Coop et al., 2024). We found that PFR in marmosets is highly consistent with humans and could be used to read-out the target motion. More so, we found that the motion in non-target apertures also influenced PFR but to a lesser extent than the target. The gain of PFR was distributed equally between target and non-target apertures before the saccade, and then was rapidly enhanced only for the target motion in driving the post-saccadic following. Thus, PFR provides a behavioral measure of target enhancement relative to distracters in addition to providing a read-out of the targets motion. Significance StatementUsing a saccade foraging paradigm in marmoset monkeys we measured visual motion integration and pre-saccadic enhancement based on the smooth following eye movements made after a saccade to a motion aperture. We find that marmosets exhibit post-saccadic following behaviors akin to humans, underscoring the evolutionary continuity in visual processing across primates. This following response provided an estimate of target motion that was half as accurate as explicitly trained reports but required minimal training to achieve. It also provided an estimate of the pre-saccadic enhancement for the target relative to distracters in the visual field.

neuroscience↗

bioRxiv2021

Beyond Fixation: detailed characterization of neural selectivity in free-viewing primates

Virtually all vision studies use a fixation point to stabilize gaze, rendering stimuli on video screens fixed to retinal coordinates. This approach requires trained subjects, is limited by the accuracy of fixational eye movements, and ignores the role of eye movements in shaping visual input. To overcome these limitations, we developed a suite of hardware and software tools to study vision during natural behavior in untrained subjects. We show this approach recovers receptive fields and tuning properties of visual neurons from multiple cortical areas of marmoset monkeys. Combined with high-precision eye-tracking, it achieves sufficient resolution to recover the receptive fields of foveal V1 neurons. These findings demonstrate the power of free viewing to characterize neural response while simultaneously studying the dynamics of natural behavior. HighlightsO_LIWe introduce a free-viewing paradigm for studying neural mechanisms of visual processing during active vision C_LIO_LIReceptive fields (RFs) and neural selectivity in primary visual cortex (V1) and area MT can be extracted during free-viewing in minimally-trained subjects C_LIO_LINovel high-resolution eye tracking in this context supports detailed measurements of receptive fields in foveal V1 C_LI

neuroscience↗