Vision, Attention and Eye Movements at the Scale of the Foveola

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PROJECT SUMMARY Humans rely on the foveola, the region of the retina where cones are most densely packed, for exploring the visual scene at high resolution. Although the foveola only covers a tiny portion of the visual field— approximately the size of a full moon—, damage to this area has devastating consequences for most daily visual activities. Yet, primarily as a consequence of technical challenges, little is known about the mechanisms of foveal vision and the sensorimotor strategies by which humans achieve high visual acuity. A major difficulty in studying foveal functions comes from the need to finely control retinal stimulation. At this scale, both placing and maintaining a stimulus at a desired eccentricity is difficult, because of uncertainty in localizing the center of gaze (typically as large as the foveola itself), and because of the continual retinal motion caused by fixational eye movements, the slow eye drifts and small saccades that humans continually perform. The PI and her coworkers have recently circumvented these limitations and developed new methods for mapping visual functions at the very center of gaze. Their research has shown that pattern vision varies sharply across the foveola, and that both attention and eye movements are precisely controlled at this scale. These previous findings raise a fundamental hypothesis: high acuity vision does not follow automatically from placing the stimulus on the foveola, but it is the outcome of an orchestrated synergy of visual, motor, and attentional components, which closely cooperate to sequentially extract fine spatial information from the foveal region. This project is designed to investigate this hypothesis, in three strongly inter-connected aims, we will examine the role of attention in high acuity vision (Aim 1), how it is modulated by microsaccades (Aim 3), and how both attention and microsaccades deal with limits in visual processing of fine patterns (Aim 2). Specifically, in Aim 1, we will build upon our previous work on the fine control of voluntary attention within the foveola and study the spatial resolution of this phenomenon, its temporal dynamics, and whether it extends to involuntary attention. In Aim 2, we will map visual acuity across the foveal space and examine how visual acuity and crowding vary within the foveola. In Aim 3, we will investigate the accuracy and precision of mi- crosaccades, their contributions to alleviating physiological limitations in acuity and crowding, and their links to attentional control within the foveola. The interplay of vision, attention, and oculomotor activity will be stud- ied not just in general terms (average results across observers) but also at the individual level, to determine whether the degree of attentional and motor control covary and whether the latter is linked to idiosyncratic differences in acuity. Our main hypothesis that fine spatial vision is the outcome of a sensorimotor interaction bears several important consequences. It raises the possibility that sub-optimal control of attention and fixa- tional eye movements may contribute to high acuity impairments. This research may open the way for visual rehabilitation procedures that act on the fine control of eye movements and attention.