UC Berkeley

Abstract

Spatial and Color Vision in the Absence of Retinal Motion

by

Alexandra Elizabeth Boehm

Doctor of Philosophy in Vision Science

University of California, Berkeley

Professor Austin Roorda, Chair

In the mid-19th century, Johannes Peter Müller first proposed what has become known as the law of specific nerve energies, where sensory perception is understood in the context of underlying physiological mechanisms which create an internal representation of an external stimulus. In the Handbuch der Physiologie des Menschen für Vorlesungen he wrote, “Sensation is not the conduction of a quality of state of external bodies to consciousness, but the conduction of a quality or state of our nerves to consciousness, excited by an external cause,” (translated by Clarke & O’Malley, 1996). While it has long been appreciated that visual perception and the underlying physiology are inextricably linked, scientific research has been limited in its ability to provide direct comparisons between the two. Perception is the culmination of multiple levels of neural processing involving millions of cells, but physiological models are often limited to data from a single or few cells in nonhuman primates. In contrast, what we know about perception has largely been gathered from psychophysical experiments performed in humans, where behavior is quantified and related to controlled differences in external stimuli, but the underlying physiological mechanisms can only be inferred.

For vision, this is further complicated by the fact that the eye is constantly in motion. Even when fixated, the eye makes microscopic eye movements which cause light from a stationary stimulus to be moved across many light-sensitive cells on the retina, and consequently across many receptive fields of downstream neurons. Recent advances in optics and eye tracking technology have made it possible to perform psychophysical experiments in human observers with cellular resolution where stimuli are fixed on the retina even in the presence of eye motion. This has brought about a new generation of experiments attempting to unify physiology and behavior. The work described here utilizes and expands upon these methodologies toward a better understanding of color and spatial vision in the absence of retinal motion. Chapter 1 provides a background on the origins of color and spatial vision in the retina, in addition to a review of the methodology. Chapter 2 explores the spatial extent of desensitization to stabilized stimuli and compares this to the known constraints to spatial vision imposed by anatomy and physiology. Chapter 3 expands upon previous work, looking at the contribution of individual cone photoreceptors to color vision, toward the construction of physiologically relevant color space from multiple cone-targeted stimulation. Finally, Chapter 4 demonstrates novel methodology to compensate for stimulus motion on the retina that is due to dynamic changes in transverse chromatic aberration.