Geoffrey Bingham, Ph.D. - US grants

How do people perceive the size of objects visually? Since the size of the visual image of an object varies depending on the distance of the object from the observer, this has always been a problem for perceptual theorists. One possibility is that people know the size of familiar objects that they can recognize from their shapes. An important category of recognizable objects consists of biological objects whose sizes vary with growth. Physical laws that constrain growth processes produce subtle changes in the shape of biological objects that correspond to changes in their sizes. Specific shapes, therefore, correspond to specific sizes. Is it possible that observers can discriminate these subtle variations in shape and use them as visual information about size? This research will investigate two physically determined aspects of tree shape as information about tree height. Observers will judge computer-generated tree silhouettes appearing without any other visual information about size or distance. All silhouettes will be of the same image size. The research will use a computer model derived from biophysical studies of tree growth. The research will compare results with the computer-generated tree silhouettes to perceptual results with silhouettes of real trees and with judgments of real trees in natural viewing conditions. Tree motions also vary in ways specific to tree size, due to some of the same physical constraints determining tree shape. The research will isolate these motions in patch-light displays, in which only the tips of the branches can be seen moving, and test their role as visual information about size. Results of these studies will contribute to an understanding of scaling in space perception, especially in circumstances where distance information is perturbed, as in looking through telescopes or other imaging apparatus. Previous research has shown that motions from a variety of simple physical events appearing in patch-light displays can enable visual recognition of the events, while static images from the displays are unrecognizable. What characteristics of motions can observers discriminate and use as information about events? The second part of this research will manipulate motions in computer- generated displays via dynamical models of these simple events. The importance of using dynamical models in this way is that they capture the physical properties of events that determine the motions specific to an event. The simulations will test the ability of observers to discriminate different types of motions and to recognize different events and event properties. The results will be especially relevant to understanding visual recognition in situations where only low frequency spatial patterns are available, as in vision with cataracts or with night vision goggles.

DESCRIPTION (Applicant's Abstract): Many studies have revealed distortions in the visual perception of the distance and shape of objects. In view of this, how do people successfully reach to grasp objects? The stability of reaching is also at issue because reaching drifts without haptic feedback from contact with objects. Previously, the investigators have argued that calibration is an essential component of definite distance perception. However, studies of haptic shape perception have also revealed distortions in perceived shape. They will investigate how haptic and visual perception of egocentric distance and shape are combined to allow stable and accurate reaching and grasping. Target spheres will be viewed by participants and then removed by the experimenter before the participant performs blind reaches. Participants will reach to locations at small exocentric distances to the front, back, top, or bottom of a target sphere or reach to location on the surface of the sphere itself. In some conditions, participants will be allowed haptic feedback and in other not. They will investigate stability based on haptic information along and whether vision destabilizes reaching once haptic feedback is removed. They will investigate if the presence of a continuous visible surface facilitates generalization of haptic calibration across reach space. The investigators will examine whether grasping allows greater accuracy and stability than reaching. Finally, they will investigate monocular optic flow generated by head movement. Twenty percent of the general population is estimated to be effectively monocular. The best monocular perception of distance is achieved via optic flow generated by self-motion. They will use head mounted computer graphics displays to rescale the relation between optic flow and self-motion and use the rescaling to investigate the locus and specificity of calibration. This program of research is unique in it attention to both the perceptual and motor side of manual activity and to the inherently multimodal character of spatial behavior. By studying the integrated function of vision and haptics and motor control the investigators hope to generate fundamental understanding of functionally effective spatial behaviors.

DESCRIPTION (provided by applicant): We study space perception and reaching. How might dynamic monocular and binocular vision yield accurate and stable perception of the distance, size and shape of objects to guide reaching effectively? Distortions are found consistently in passive judgment studies. In our studies, participants moved their head to generate optic flow while they viewed a spherical target. Then, they reached to touch the front, left, right or back of the sphere. We found distortions and instability. We tested whether calibration by touching a target would correct distortions. Distance was corrected, but shape was not. Using a Virtual Reality (VR) lab, we now investigate the use of visual and haptic feedback to calibrate distance, size and shape perception. We first compare and confirm in the virtual environment the results obtained in actual environments and we establish the functional effects of accommodation/vergence and IPD variations in VR. We use VR to measure and then to eliminate the use of disparity matching and thus isolate binocular distance and shape perception with concurrent vision of a target during a reach. Participants will reach to visible targets with an invisible hand. We investigate whether distance and shape distortions reflect a single continuous transformation of reach space or are independent. We investigate whether visual feedback from a near object generalizes to a far object both without and with a visible intervening support surface. We test the calibration of newly discovered eye height scaled information about distance along a flat surface. We test how quickly errors appear after calibration is removed. Using distorted haptic feedback, we test the strength of the coupling between haptic feedback and visual information about distance, while varying the strength of visual information. Finally, we test whether calibration is limited to the limb used to obtain feedback or generalizes to another limb. Can two limbs simultaneously be calibrated in different ways by distorted haptic feedback? Next, we investigate 3 ways that accurate shape perception might be achieved. First, we test whether objects with planar surfaces might allow observers to use contour invariants to achieve correct shape. Second, we test whether a visible support surface yields accurate shape perception because it introduces wide angle structure and large internal depth structure. Third, we test whether feedback might be effective for slant perception as a form of shape perception that allows feedback about shape to be provided in a single reach.

DESCRIPTION (provided by applicant): This application requests support for a program of basic and clinical research on Developmental Coordination Disorder (DCD) and sensori-motor learning. The primary objective of this project is to understand how barriers to effective motor learning created by sensori-motor deficits can be overcome to enable children with DCD, and other developmental disorders often co-morbid with DCD, to learn to perform good compliant manual actions and especially, handwriting. The proposed research will involve behavioral studies of sensori-motor learning. Four specific aims will be studied: (1) learning with assistance; (2) generalization from assisted practice and retention; (3) passive versus active practice; and (4) task specific practice. The research findings will provide a much stronger conceptual and theoretical basis for explaining the problems faced by children with DCD and other co-morbid developmental disorders with origins in sensori-motor deficits. The results from this project will also have important direct clinical implications for design of therapeutic training for children with sensori-motor disorders. Furthermore, the results are anticipated to enable future efforts to pursue the developmental effects of sensori-motor deficits on cognitive function and emotional experience. PUBLIC HEALTH RELEVANCE: The objective of this research project is to understand how barriers to effective motor learning created by sensori-motor deficits in Developmental Coordination Disorder (DCD) can be overcome to enable children with DCD, and developmental disorders often co-morbid with DCD, to learn to perform good drawing movements and handwriting. The results will contribute to a theoretical basis for explaining the problems faced by children with DCD with direct implications for the design of therapeutic training for these children.