STEREO AND VERNIER ACUITIES FOR MOVING LINE STIMULI AT A RANGE OF VELOCITIES

Mahalakshmi Ramamurthy

Abstract

PURPOSE. A previous study reported little effect of lateral motion on line stereoacuity, but the velocity of the targets was restricted to 2.5 deg/s or less. The goal of this study was to examine the influence of lateral target motion on stereo acuity for a wider range of velocities, and compare the results to those obtained for moving Vernier targets with the same configuration.

METHOD. The stereotargets were composed of 2 bright vertical lines, separated vertically by 5 or 20 min arc. The targets were presented foveally for 200 ms, at a horizontal velocity of motion that ranged from 0 to 12 deg/s. Both the direction of motion (right vs. left) and the horizontal image disparity varied randomly from trial to trial. Thresholds corresponding to 84% discrimination were determined by probit analysis from forced choice responses obtained with the method of constant stimuli. Vernier thresholds were measured under identical conditions, except that the horizontal offset between the top and bottom lines was always identical in the dichoptically presented Vernier stimuli.

RESULTS. Data for two normal subjects show that stereo and Vernier acuity worsen similarly with image velocity. An equivalent blur analysis indicated that stereo and Vernier thresholds each tolerate lateral image motion of 1.5 to 2 deg/s without degradation. At higher velocities, stereo and Vernier thresholds both increase in proportion to the speed of the target.

CONCLUSIONS. Substantial evidence indicates that stereo and Vernier acuity are mediated by different neuronal mechanisms. Our finding that lateral motion degrades both forms of acuity similarly suggests that the effect of motion occurs at a relatively early stage of visual processing.

Details

Year: 2001

Program Number: 2:00 pm

Author Affiliation: University of Houston

Co-Authors: Harold Bedell, Saumil Patel, Michael Ukwade

Co-Author Affiliation: University of Houston, University of Houston, University of Houston

Room: Room 108