Search

Eye movements of adult hemiplegics (11 right- and 9 left-brain-damaged patients) and 11 nonimpaired controls were recorded as they viewed selected cards of the Motor-free Visual Perception Test. The major finding was that neither group of patients exhibited an asymmetry of visual exploration (unilateral visual neglect) as they viewed the cards. Their scanning strategies were, however, unsystematic and irregular. In addition, both groups of patients scanned the cards longer and made more errors than controls. Use of the Motor-free Visual Perception Test as an appropriate measure for the general assessment of visual-perceptual processing abilities of adult brain-damaged patients who lack severe clinical manifestations of neglect is discussed.

Two experimental approaches examined observers' ability to characterize shape symmetry based upon the information obtained within a single fixation. Exp. I tested observers' ability to discriminate among three levels of symmetry on the basis of a 25-msec. presentation. Results indicated that identification accuracy was higher for symmetrical and asymmetrical shapes than for mixed shapes, which contained both symmetrical and asymmetrical components. Exp. II tested observers' ability to detect a given level of symmetry by means of a signal-detection approach. Symmetrical shapes were detected better than asymmetrical shapes. Detectability of mixed shapes was lower than that for both symmetrical and asymmetrical shapes. The results of Exps. I and II demonstrate that observers can characterize shape symmetry on the basis of information available within a single fixation. The data are supportive of the hypothesis that a global response to the over-all configuration of the shape serves to facilitate form perception.

The influence of amount and type of exploratory activity upon 3 male and 5 female undergraduates' ability to detect the symmaterical or asymmetrical characteristics of individually presented plastic nonrepresentational shapes was examined. A decrease in scanning time and number of identification errors between the first and fourth days of testing indicates that extended perceptual experience plays a major role in the efficient pick-up and utilization of haptic information. A signal-detection analysis demonstrated that the use of a simultaneous-apprehension scanning strategy resulted in greater sensitivity to asymmetrical shapes than did the use of a simultaneous-apprehension scan. The data support the hypothesis that experience, the form parameter of symmetry, and the type of scanning strategy used to explore a stimulus function together to influence haptic perception of nonrepresentational shapes.

Sighted subjects (n = 15) assembled 6-piece jigsaw puzzles under four conditions of visual-haptic perception which both separated these perceptual systems and required the simultaneous use of vision and touch. The time required and haptic scanning strategies used to assemble the puzzles in each of the four conditions were examined to determine the influence of type of visual involvement upon haptic encoding processes and the degree to which the visual and haptic systems are linked. Results indicate that a cognitive component is involved during visual-tactual form perception which affects how the perceptual modalities work together and how information is selected, encoded, and processed. When vision and touch were used simultaneously to examine the same stimulus, and visual information was adequate for responding, vision dominated touch. However, in conditions of visual-haptic perception in which visual input was inadequate for responding or when haptic perception was independent of vision, subjects relied upon a form of information which was specifically tactual in nature and independent of visual or verbal recoding.