Russell L. De Valois - US grants

9309826 De Valois The visual system is able to distinguish several spatial features of visible objects, including form, texture and motion. The visual cortex of the brain has been subdivided into a many different areas based on both anatomical and functional criteria. There are physiological recordings showing the activity responses in the brain to visual stimuli, but the nature of how that cortical organization relates to the process of "seeing" is complex and not yet clear. Psychophysical tests use quantitatively well-defined optical stimuli while measuring responses to properties such as detectability or discriminability. This project uses identical stimuli for psychophysical tests and for physiological tests to determine directly to what extent the nerve cells in various levels of the cortex participate in processing patterns. Novel stimuli are exploited that incorporate patterns with the spatial components filtered in various quantifiably specified ways. In particular, the question of whether fundamentally different processes are used in texture discrimination and form discrimination will be addressed. Results will be valuable to our understanding of how the brain processes information, and will have an impact on visual neurobiology and more broadly to neuroscience, with likely application to computational vision, to artificial vision architecture and to visual display systems. ***

The goals of the proposed research are to increase our understanding of the way in which the visual system processes information based on color differences and to investigate visual responses to patterns which contain both color and luminance variations. Experiments addressing the former will consist in part of psychophysical and electrophysiological studies of selectivity for patterns which vary only in chromaticity along different spatial dimensions such as spatial frequency and orientation. These will be compared to selectivity for similar isochromatic luminance-varying patterns. Other studies will attempt to relate threshold sensitivity to color differences to suprathreshold color perception involved and study the underlying cortical organization in both color-normal and color-deficient subjects. The proposed studies of color-luminance interactions will be of several kinds. Psychophysical masking experiments will examine the effect of luminance contrast on the detectability of various chromatic patterns, and vice versa. Contrast, spatial frequency and orientation of the various patterns will be systematically varied. In physiological experiments the sensitivity of single cortical cells to chromatic variations will be measured both alone and in the presence of luminance contrast. The converse will also be done.

This research project consists of a series of electrophysiological and psychophysical studies of certain aspects of spatial vision. In studies of the striate cortex (cortical area V1), the investigators propose to examine the arrangement of cells tuned to various orientations and spatial frequencies in relation to the cytochrome oxidase blobs marking the cortical modules. The investigators also plan to examine how the spatial frequency tuning and phase-specificity of striate cells vary with eccentricity. In studies of cells in the second cortical visual area (V2), it will be determined how these cells respond to simple patterns which well characterize V1 units, and to somewhat more complex patterns, to explore possible transformations occurring in information processing at this level. In the psychophysical experiments, the investigators will examine certain aspects of human ability to localize patterns independent of the characteristics of the patterns, and to study some problems of pattern discrimination which depend on ratio judgments. Both of these problem areas were chosen to explore in perceptual experiments certain issues which have arisen in considering the possible roles of cells in cortical areas V1 and V2. The results of this research project will contribute important information to our knowledge of visual information processing by the brain.

The visual system is among the most accessible and readily studied parts of the nervous system. Understanding it will greatly increase our ability to understand the brain as a whole. The research proposed in this application is aimed at increasing our basic understanding of color vision, in particular, and the organization and development of the nervous system in general. The experiments proposed here will help resolve some of the conflicts evident in presently-accepted theoretical and experimental accounts of color. Studies of the possible existence of asymmetric opponent mechanisms will aid in determining the adequacy of current accounts and, if necessary, in improving them. Both psychophysical studies with human observers and electrophysiological studies from macaque monkey will be coordinated and correlated to increase the power of the results from each alone. Some experiments will examine the existence and characteristics of the color-selective mechanisms that respond to intensity contrast. No full understanding of intensity contrast vision is possible without elucidating the role of these mechanisms. Other studies proposed will examine the processing of visual motion-- one of the most important of the visual abilities--at isoluminance. Color motion vision is remarkably and curiously deficient. To understand this will allow a much greater understanding of the visual processing of motion in general and of the peculiarities associated specifically with the anatomical substrate that is responsible for color vision. Motion vision in the color system will be studied by a variety of psychophysical experiments using isoluminant patterns. These experiments will have counterparts in physiological studies designed to use the same stimuli and similar methods. This will make it possible to develop a much fuller and more thorough understanding of the system.

The visual system is among the most accessible and readily studied parts of the nervous system. Understanding it will greatly increase our ability to understand the brain as a whole. The research proposed in this application is aimed at increasing our basic understanding of color vision, in particular, and the organization and development of the nervous system in general. The experiments proposed here will help resolve some of the conflicts evident in presently-accepted theoretical and experimental accounts of color. Studies of the possible existence of asymmetric opponent mechanisms will aid in determining the adequacy of current accounts and, if necessary, in improving them. Both psychophysical studies with human observers and electrophysiological studies from macaque monkey will be coordinated and correlated to increase the power of the results from each alone. Some experiments will examine the existence and characteristics of the color-selective mechanisms that respond to intensity contrast. No full understanding of intensity contrast vision is possible without elucidating the role of these mechanisms. Other studies proposed will examine the processing of visual motion-- one of the most important of the visual abilities--at isoluminance. Color motion vision is remarkably and curiously deficient. To understand this will allow a much greater understanding of the visual processing of motion in general and of the peculiarities associated specifically with the anatomical substrate that is responsible for color vision. Motion vision in the color system will be studied by a variety of psychophysical experiments using isoluminant patterns. These experiments will have counterparts in physiological studies designed to use the same stimuli and similar methods. This will make it possible to develop a much fuller and more thorough understanding of the system.

De Valois/ De Valois (0111059)

Studies of Motion Vision

Lay Abstract

This project is designed to increase our understanding of how the brain analyzes visual motion. Telling the difference visually between stationary and moving objects is a very difficult problem. The physiological responses of neurons in the visual system of macaque monkeys to stationary and moving objects will be examined and compared to the behavioral responses of human observers in similar tasks. Two major subtopics will be considered.
An early step in the analysis of visual motion is the creation in the first visual cortical area (V1) of directionally-selective neurons, neurons that respond only if an object moves in a particular direction within the limited visual region from which the cell receives inputs. One topic of investigation will be how these cells are created; in particular, where do their inputs come from and how are they combined to produce directional selectivity. A specific model will be tested by several experiments on both directional V1 cells and on the cells in the lateral geniculate nucleus (LGN) that provide inputs to the directional cells. The results of these experiments will be compared to the results from related psychophysical studies on human observers.
A second topic will be the way the color-vision system provides input to or interacts with the visual motion system. Psychophysical experiments on human observers will examine the effects of color alternation on the discrimination of the direction of motion of a luminance-varying grating. Different chromatic combinations will be used, including those that preferentially excite specific classes of photoreceptors or neurons in the LGN. Earlier work predicts differential effects for different color combinations. Physiological studies will examine the effects of color alternation on the responses of directionally-selective neurons in V1 for comparison to behavioral responses from humans.
These studies will significantly advance our understanding of the initial mechanisms of the visual motion system in humans and other primates. In addition to increasing our knowledge of the brain and its organization, this work will contribute to the advancement of health and human understanding. The fuller understanding gained from these studies may also have direct application in the design of lighting systems, particularly for moving vehicles, and in other situations in which human factors concerns are significant.
This project will contribute to the scientific education and training of both undergraduate and graduate students. Graduate students will be involved in the design, performance, analysis and publication of these studies. Undergraduate students will work as laboratory technicians and psychophysical subjects. When possible, they will also be involved in the design, performance, analysis and publication of the studies. Many former graduate students who have worked on similar projects in these laboratories have built distinguished careers in the study of vision. Several former undergraduates who have worked in these laboratories have become health workers or scientists. Students employed on similar projects in the past have come from both genders and many ethnic groups. This research, like previous work in these laboratories, is expected to increase the opportunities for students from minority groups to participate in scientific research and prepare for future careers of their own.