Leonard Matin - US grants

The fundamental problem to which a strabismic must adapt centers about dealing with two disparate pieces of information regarding the location of an object from a visual system whose geometry, anatomy, and physiology indicate that it was designed to yield only one perceived location for each point in three-dimensional space. There is a paucity of systematic work aimed at the primary aspect of perception that relates to visual localization in the frontal plane. The present proposal is aimed at measuring binocular and monocular visual localization in the frontal plane. Monocular visual localization will be measured with each eye using auditory/visual matching of locations. The monocular judgments will be compared with localizations made by dichoptically matching two visual targets simultaneously. Previous work informs us that extraretinal eye position information (EEPI) will play a major role in controlling monocular egocentric and intersensory localization through the Cancellation Mechanism; but we have reason to believe that this will not be so in the dichoptic match, where it is anticipated that the mode of control of the mechanism generating visual localization will itself be different. Thus, intransitivities among the different measurements are anticipated. These intransitivities will throw light on anomalous retinal correspondence (ARC). Since we have already shown that flexibility in EEPI is involved in localization by the strabismic, the present work will build on that. Some of this work is aimed at uncovering the main basis for ARC. A model for control of visual localization that is derived from and closely tied to previous experiments on normal and curarized observers and strabismics will guide the research. The model extends the classical Cancellation Mechanism in new directions.

This continuing grant for three years supports research on how visual information is used for human spatial orientation. One of the three main spatial dimensions basic to spatial location, direction, and orientation is "elevation." Cues about the direction of "up" and "down" are usually present in the visual world. For the brain to evaluate these visual cues, there needs to be "extra.retinal" information on the position of the eyes within the head. In addition, information about head and body position comes from internal position receptors in the body, called proprioceptors, including the gravitational receptor system of the inner ear and joint and stretch receptors in the body. The relative role of these different systems has not been worked out, but there is some evidence that in humans vision makes a larger contribution than those non.visual cues. A theoretical approach is developed for the principles by which visual field structure influences the perception of elevation. Quantitative predictions from the theory will be tested on subjects placed in a room which can be pitched forward or back, using visual stimuli that are erect or pitched relative to the observer who will be erect or pitched at one of several angles. Measurements will be made on how pitch of the visual field influences perceived eye level, or perceived elevations of visual objects, or perceived slant of the visual field, or perceived pitch of the subject's body. These influences will be tested under conditions that produce substantial distortions of perception. The importance of central and peripheral vision, and perception of size constancy also will be assessed. This work will clarify how we establish the relative spatial orientation between objects and self, which is a fundamental issue of perception, and an issue of how input from several senses is integrated. This research is likely to have application to the design and operational criteria for visual guidance of machines such as industrial cranes and piloted vehicles.

DESCRIPTION: The proposed research involves a series of experiments aimed at delineating the mechanisms controlling egocentric visual orientation with particular emphasis on (a) visual perception of elevation, (b) visual perception of orientation in the frontal plane (c) visual localization in the horizontal dimension, and (d) the relationships between these three. The experiments are organized around a model (the Great Circle Model) which deals with how influences of oriented lines in the visual field combine to determine three perceptual norms: visually perceived eye level, visually perceived vertical, and visually perceived straight ahead. Other experiments concern the way in which body related and visual information combine. Eight sets of experiments are proposed. The first set extends previous findings on visually perceived eye level to measurement of influences on visually perceived vertical, and asks whether these influences are retinotopic or not. Other experiments examine how the effects of various oriented lines combine, and how sets of linearly arrayed points summate to affect visually perceived eye level. A fourth set of experiments deals with the rise and decay of the influence of the visual field. The fifth set explores the effect of body orientation on visually perceived eye level and visually perceived straight ahead. Two sets of experiments examine the role of binocular stimulation and other information about surface orientation. A final set looks at the role of eye position information.

A primary means by which humans interact with the physical world is by coordinating the hands with the eyes and the body. We reach out to manipulate objects, and often those objects are manipulated relative to the body (like when one reaches out for food while eating). The visual and motor systems have evolved in the context of such task demands, resulting in an intimate coordination between these and other sensorimotor systems. When the inputs to each system go out of alignment, either due to natural circumstances or manipulations in the laboratory, the result can be a perceptual illusion. Perceptual scientists have examined such illusions for over a hundred years as sources of evidence about the underlying sensorimotor mechanisms.

With support of the National Science Foundation, Dr. Matin will investigate a newfound illusion that arises from the interaction of visual and motor systems. Under certain conditions, a person will visually misperceive the location of an object at arm's length, even though the person can point to it accurately with a fully extended arm. Dr. Matin's research project will examine this illusion from an action-oriented perspective. The results promise to advance our understanding of the coordination between perception and action, and may provide basic knowledge that is useful for understanding perceptual-motor dysfunctions that can occur as a result of injury or disease.