During visual fixation, small eye movements of which we are usually not aware, prevent the maintenance of a steady direction of gaze. It is known that images tend to fade when retinal motion is eliminated in the laboratory. However, it has long been debated whether, during natural viewing, fixational eye movements do more than prevent the visual scene from fading. The results of experiments conducted during a previous Grant for Pilot Research indicate that fixational eye movements contribute to the perception of fine spatial detail, as predicted by our models and as speculated for more than a century. This proposal describes a program of research, which combines psychophysical experiments with human subjects, computational modeling of neurons in the early visual system, and statistical analysis of the visual input the retina to study the contributions of fixational eye movements in pattern vision. Psychophysical experiments will examine the detection and discrimination of stimuli presented, with and without retinal image motion, during the brief intersaccadic periods of natural visual fixation. To overcome the technical limitations of previous studies on retinal stabilization, experiments will rely on a new system of gaze-contingent display, which enables rigorous comparison between the two conditions of normal retinal motion and retinal stabilization. This system enables us to (a) selectively stabilize the stimulus after a saccade, a condition that preserves the normal fixational motion of the eye, (b) randomly alternate trials with and without retinal image motion, and (c) assess the accuracy of retinal stabilization independently of the subject's own judgment. Computational studies will examine the visual input signals experienced by subjects in the experiments, and simulate the responses of neurons in the retina, the lateral geniculate nucleus, and the striate cortex. For every experimental trial, a simulation will replicate neuronal activity during the sequence of eye movements performed by the subject. Subject performance and information about the stimulus transmitted by neuronal responses will be compared on a trial-by-trial basis. A number of visual disorders manifest abnormal fixational eye movements. In addition to advancing our basic understanding of visual perception, a comprehension of the functional implications of fixational instability may lead to treatment of the visual impairments commonly associated with such conditions.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IFCN-B (04))
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Steinmetz, Michael A
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Boston University
Schools of Arts and Sciences
United States
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Fang, Yu; Gill, Christopher; Poletti, Martina et al. (2018) Monocular microsaccades: Do they really occur? J Vis 18:18
Rucci, Michele; Victor, Jonathan D (2018) Perspective: Can eye movements contribute to emmetropization? J Vis 18:10
Rucci, Michele; Ahissar, Ehud; Burr, David (2018) Temporal Coding of Visual Space. Trends Cogn Sci 22:883-895
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Ko, Hee-Kyoung; Snodderly, D Max; Poletti, Martina (2016) Eye movements between saccades: Measuring ocular drift and tremor. Vision Res 122:93-104
Mostofi, Naghmeh; Boi, Marco; Rucci, Michele (2016) Are the visual transients from microsaccades helpful? Measuring the influences of small saccades on contrast sensitivity. Vision Res 118:60-9
Poletti, Martina; Rucci, Michele (2016) A compact field guide to the study of microsaccades: Challenges and functions. Vision Res 118:83-97
Rucci, Michele; Poletti, Martina (2015) Control and Functions of Fixational Eye Movements. Annu Rev Vis Sci 1:499-518

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