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1. Detailed characterization of neural selectivity in free viewing primates.

Author

Yates, Jacob, Coop, Shanna, Sarch, Gabriel, Wu, Ruei-Jr, Butts, Daniel, Rucci, Michele, and Mitchell, Jude

Subjects
Animals, Visual Cortex, Visual Fields, Vision, Ocular, Eye Movements, Haplorhini, Photic Stimulation
Abstract

Fixation constraints in visual tasks are ubiquitous in visual and cognitive neuroscience. Despite its widespread use, fixation 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 measured visual receptive fields and tuning properties from multiple cortical areas of marmoset monkeys who freely viewed full-field noise stimuli. The resulting receptive fields and tuning curves from primary visual cortex (V1) and area MT match reported selectivity from the literature which was measured using conventional approaches. We then combined free viewing with high-resolution eye tracking to make the first detailed 2D spatiotemporal measurements of foveal receptive fields in V1. These findings demonstrate the power of free viewing to characterize neural responses in untrained animals while simultaneously studying the dynamics of natural behavior.

Published
2023

10. Eye blinks as a visual processing stage.

Author

Bin Yang, Intoy, Janis, and Rucci, Michele

Subjects
BLINKING (Physiology), EYE movements, EYE tracking, NEURAL pathways, SPATIAL behavior
Abstract

Humans blink their eyes frequently during normal viewing, more often than it seems necessary for keeping the cornea well lubricated. Since the closure of the eyelid disrupts the image on the retina, eye blinks are commonly assumed to be detrimental to visual processing. However, blinks also provide luminance transients rich in spatial information to neural pathways highly sensitive to temporal changes. Here, we report that the luminance modulations from blinks enhance visual sensitivity. By coupling high-resolution eye tracking in human observers with modeling of blink transients and spectral analysis of visual input signals, we show that blinking increases the power of retinal stimulation and that this effect significantly enhances visibility despite the time lost in exposure to the external scene. We further show that, as predicted from the spectral content of input signals, this enhancement is selective for stimuli at low spatial frequencies and occurs irrespective of whether the luminance transients are actively generated or passively experienced. These findings indicate that, like eye movements, blinking acts as a computational component of a visual processing strategy that uses motor behavior to reformat spatial information into the temporal domain. [ABSTRACT FROM AUTHOR]

Published
2024
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11. Temporal sensitivity in the central fovea

Author

Lin, Ruitao, primary, Benedetto, Alessandro, additional, Intoy, Janis, additional, Moon, Benjamin, additional, Clark, Ashley M., additional, Jenks, Samantha K., additional, Kapisthalam, Sanjana, additional, Poletti, Martina, additional, and Rucci, Michele, additional

Published
2023
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14. Microsaccades in head-free high-acuity tasks

Author

Jolly, Paul, primary, Li, Yuanhao H., additional, Cox, Michele A., additional, Clark, Ashley M., additional, Yang, Bin, additional, Lin, Ruitao, additional, Zhao, Zhetuo, additional, and Rucci, Michele, additional

Published
2023
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20. Task-driven influences on fixational eye movements

Author

Victor, Jonathan, Lin, Yen-Chu, Rucci, Michele, Victor, Jonathan, Lin, Yen-Chu, and Rucci, Michele

Abstract

There is now compelling evidence that the spatiotemporal remapping carried out by fixational eye movements (FEMs) is an essential step in visual processing. Moreover, the overall Brownian-like statistics of FEMs are calibrated to map fine spatial detail into the temporal frequency range to which retinal circuitry is tuned. Here, we tested the hypothesis that the detailed spatial characteristics of FEMs can be adjusted to task demands via cognitive influences that operate even in the absence of a visual stimulus. We examined FEMs in a task that required subjects (N=6) to report which of two letters was displayed. Trials were blocked; in each block, the letter pair was known in advance: H vs. N or E vs. F. The task was demanding: letters were 1.5 deg and embedded in 1/f noise, and had a contrast that yielded ~75% correct performance. Note that the HN discrimination could be accomplished by identification of either a horizontal or oblique contour, but the EF discrimination required identification of a horizontal contour. Thus, in the EF blocks, only a vertical ocular drift would be expected to maximize the neural signal. For each condition, FEM velocity statistics, which were approximately Gaussian, were characterized by their covariance. As predicted, the ratio of velocity variance in the vertical vs. oblique direction was greater in EF trials than in HN trials. This difference was greater when no stimulus was present (20% of trials in each block), indicating open-loop control. We also found that single-trial drift trajectories could be decoded by a simple decoder to identify the task (HN vs. EF) at above-chance levels in most subjects. While the observed covariance patterns showed substantial inter-subject variability, we found that a single transformation, applied with subject-specific strengths, could largely account for all subjects’ findings. Critically, this shared transformation acts holistically on the plane, rather than individually on horizontal and vertical

Published
2023

41. Miniature eye movements enhance fine spatial detail

Author

Rucci, Michele, Iovin, Ramon, Poletti, Martina, and Santini, Fabrizio

Subjects
Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Author(s): Michele Rucci (corresponding author) [1]; Ramon Iovin [1]; Martina Poletti [1]; Fabrizio Santini [1] Our eyes are constantly in motion. Even during visual fixation, small eye movements continually jitter [...]

Published
2007
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46. Contrast sensitivity reveals an oculomotor strategy for temporally encoding space

Author

Casile, Antonino, Victor, Jonathan, and Rucci, Michele

Subjects
0301 basic medicine, retina, Time Factors, genetic structures, Visual system, chemistry.chemical_compound, 0302 clinical medicine, Rhesus macaque, Biology (General), media_common, Neurons, General Neuroscience, 05 social sciences, General Medicine, medicine.anatomical_structure, Visual Perception, Medicine, Female, Spatial frequency, Research Article, Computational and Systems Biology, Human, Adult, QH301-705.5, Science, media_common.quotation_subject, Sensory system, Fixation, Ocular, Motor Activity, Stimulus (physiology), Biology, Retinal ganglion, 050105 experimental psychology, General Biochemistry, Genetics and Molecular Biology, Young Adult, 03 medical and health sciences, Perception, medicine, Humans, 0501 psychology and cognitive sciences, contrast sensitivity, Retina, General Immunology and Microbiology, Eye movement, Retinal, eye diseases, systems modeling, eye movements, 030104 developmental biology, chemistry, Space Perception, sense organs, Neuroscience, 030217 neurology & neurosurgery
Abstract

The contrast sensitivity function (CSF), how sensitivity varies with the spatial frequency of the stimulus, is a fundamental assessment of visual performance. The CSF is generally assumed to be determined by low-level sensory processes. However, the sensitivities of neurons in the early visual pathways, as measured in experiments with immobilized eyes, diverge from psychophysical CSF measurements in primates. Under natural viewing conditions, as in typical psychophysical measurements, humans continually move their eyes, drifting in a seemingly erratic manner even when looking at a fixed point. Here, we show that the resulting transformation of the visual scene into a spatiotemporal flow on the retina constitutes a processing stage that reconciles human CSF and the response characteristics of retinal ganglion cells under a broad range of conditions. Our findings suggest a fundamental integration between perception and action: eye movements work synergistically with the sensitivities of retinal neurons to encode spatial information.

Published
2019
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47. Modeling Emmetropization in an Incessantly Moving Eye

Author

Rucci, Michele and Victor, Jonathan D

Subjects
hyperopia, retina, genetic structures, visual acuity, Developmental Neuroscience, Myopia, sense organs, Systems Neuroscience, ocular drift, saccade, eye diseases
Abstract

Many questions remain unanswered regarding the specific cues and mechanisms for emmetropization, the process by which, during development, the eye adjusts itself so that distant objects are in focus. Research has so far primarily focused on the spatial cues present in the image on the retina, such as the degree of blur. However, eye movements incessantly transform a mostly static scene into temporal modulations, so that the input to the retina is not an image, but a spatiotemporal flow of luminance. Models of retinal input signals indicate that this space-time reformatting caused by eye movements yields additional cues to the ones traditionally considered for emmetropization. These cues are implicit in the temporal modulations impinging onto retinal receptors and depend on the optics and shape of the eye and the spatial statistics of the visual scene. Here we examine the characteristics of these signals in the presence of normal eye movements and model the possible consequences of abnormal oculomotor behavior in the development of myopia and hyperopia.

Published
2018

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