Publication Date

Spring 2018

Advisor(s) - Committee Chair

J. Farley Norman (Director), Andrew Mienaltowski, and Matthew Shake

Degree Program

Department of Psychological Sciences

Degree Type

Master of Science

Abstract

The aperture problem describes an effect by which a contoured stimulus, moving behind an aperture with both ends occluded, appears to move in a direction perpendicular to its own orientation. Mechanisms within the human visual system allow us to overcome this problem and integrate many of these locally ambiguous signals into the perception of globally coherent motion. In the current experiment, younger and older observers viewed displays composed of either 64 or 9 straight contours, arranged in varying orientations and moving behind circular apertures. Because these lines moved behind apertures, their individual local motions were ambiguous with respect to direction (i.e., subject to the aperture problem). On each trial, motion patterns were displayed for 2.4 seconds, and observers estimated the coherent direction of motion (true motion directions ranged from 0 to 360 degrees). There was a significant effect of direction, such that cardinal directions of pattern motion were judged more accurately than oblique directions. In addition, there was a large effect of aging upon accuracy (the average errors of older observers were 46 and 30.4 percent higher in magnitude than those exhibited by the younger observers for the 64 and 9 aperture conditions, respectively). Additionally, the observers’ precision deteriorated markedly as the number of apertures was reduced from 64 to 9. Finally, a statistically significant, albeit negligible relationship was found between orientation discrimination threshold (a behavioral measure of resting gamma amino butyric acid neurotransmitter levels) and ability to accurately estimate coherent direction of motion.

Disciplines

Biological Psychology | Cognition and Perception | Psychology

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