Influence of Head and Eye Movements on Retinal Input and Early Neural Encoding

Trustees Of Boston University, Boston

Investigators

Abstract

Humans are normally not aware that their eyes and head are always in motion. Small involuntary head and eye movements continually occur in the periods between voluntary relocations of gaze, even when attempting to maintain steady gaze on a single point. These movements shift the stimulus on the retina in ways that would be immediately visible had the motion originated from objects in the scene rather than the observer's behavior. Building on a large body of recent findings, this project investigates the hypothesis that fixational head and eye movements are not motor instabilities, but part of a precisely controlled motor strategy that facilitates the visual processing of fine spatial detail. Elucidation of this hypothesis is important not only for advancing knowledge on the fundamental mechanisms of visual perception, but also because it implies that some visual acuity impairments may have unrecognized motor origins, and, conversely, that motor disturbances may have unsuspected sensory consequences. The research could have implications for the optimization of human visual performance in situations of restricted head movement. Also, by shedding light on how to achieve optimal sampling of visual information through coordinated movement, the research could also have implications for the design of artificial vision systems. This project will follow an integrated theoretical and experimental approach, which combines psychophysical experiments with human subjects, statistical analysis of the stimulus on the retina, and modeling of neurons in the early stages of the visual system to examine the joint consequences of head and eye movements on the acquisition and encoding of fine spatial information. Specifically, the investigators will measure fixational head and eye movements during the normal execution of high-acuity visual tasks. They will study how these movements interact, the degree of control involved in their interplay, and the nature of this interplay. In parallel, the investigators will develop quantitative predictions by reconstructing the visual input signals experienced by the observers' retinas and by analyzing the impact of these signals on the responses of computational models of neurons in the visual system. This synergy of experimental and theoretical methods will result in new knowledge in the fields of sensory perception and motor control. It will contribute critical information on the joint characteristics of fixational head and eye movements, their visual functions, and help in identifying the sensory-motor strategies by which spatial information is represented in the brain.