Research InterestsHere is a description of the research that I've pursued in recent years. (My research emphasis is changing to integrate these older interests with my newer emphasis on clinical psychology.)
The broad long-term goal of my research is to understand human visual information processing and visual development. The focus of my current research is to use individual differences in psychophysical and electro-physiological data to:
(1) Develop computational models of structures and processes underlying human vision. My previous research demonstrates that individual differences in visual performance provide valuable clues about information processing. My most recent study with Teller (to examine the nature of the coarsest spatial-frequency-tuned pattern analyzers) showed roles played by individual variability in contrast sensitivity. It revealed that contrast sensitivity functions of adults contain just one statistical source of individual variability at spatial frequencies (sinusoidal stripe width) below one cycle per degree of visual angle; that this source maps well onto the coarsest pattern analyzer from existing computational models, thus enabling determination of limits of the analyzer's tuning function. Thus individual variability can be used to derive basic units of visual information processing. I've shown that it is possible to: (a) identify statistical sources of variability that clearly reflect known perceptual or physiological processes, and (b) refine computational models of these processes using information about these sources.
(2) Analyze and delineate the developing visual system. Foci of my work include: how human vision, visual perception and cognition change over the lifespan; age-related improvement and decline of performance; neural factors underlying these changes.
My dissertation experiments (with Kaplan & Werner) stressed all three foci. Designed to measure the growth of contrast sensitivity over the first eight months of life, they tested the hypothesis that cone migration in the developing retina causes pattern analyzer shifts to progressively higher spatial frequencies during infancy. The results support the hypothesis; the methodology, based on analysis of individual variability (measured longitudinally) proved effective in relating anatomical and behavioral change.
(3) Relate behavior and physiology of human vision. My work on perceptual phenomena and neurophysiological substrates stresses the following themes: delineation of physiological processes in the intact human brain by using noninvasive methods (e.g. VEPs); the search for common subsystems underlying physiology and behavior (as revealed, for instance, by simultaneous changes in the electrophysiological and behavioral performance of the developing or aging human); application of psychophysics and noninvasive electrophysiology to the assessment of diseases of the retina and visual pathways.
My VEP experiments (with Norcia and later with Kelly and Teller) examined the cortical correlates of known perceptual (behavioral) processes. They were designed to search (in normal adults, infants, and patients) for VEP analogues of perceptual analyzers of color, motion, binocular disparity, and form (previously derived from behavioral data). The experiments showed: (a) the normal development of the cortical motion-VEP is related to directionally-selective, binocularly driven perceptual analyzers, (b) these analyzers require proper eye alignment during infancy--motion processing is intimately connected with binocular vision in a way that has not been fully appreciated by either ophthalmologists or by basic scientists, (c) spatial-frequency masking with the sweep-VEP may be explained by a discrete set of pattern analyzers derived from psychophysics, and (d) spatial processing occurs independently for color- and luminance-defined patterns. Thus, the experiments were effective in linking basic perceptual processes to cortical activity.
(4) Interrelate sensory processes and cognitive performance. My work on visual cognition aims to: delineate information-processing streams and stages; determine how sensory analyzers contribute to cognitive behaviors (e.g. pattern recognition, attention, learned contingencies); relate higher level processes (e.g. decision criteria) to sensory and perceptual performance; determine the role of pattern analyzers in subsystems that have been revealed through cognitive neuropsychology.
My work in Colorado and Berkeley (with Werner, Hardyck, Kaplan, Healy, Harvey) examined the roles of spatial pattern analyzers in various types of cognitive performance. The experiments tested the hypotheses that these analyzers play roles in determining (a) "preferences" for, or attention to, complex patterns such as faces (in infants), (b) pattern confusions during reading (in adults), and (c) visual field performance asymmetries in studies of cerebral lateralization. Results indicated that analyzers influence (a) and (b) but not (c); "low-level" sensory processing contributed to "high-level" cognition.