Purchase this article with an account.
M Ramamurthy, HE Bedell, SS Patel; Stereothresholds for Moving Targets Separated by Vertical and Horizontal Gaps . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4677.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: One goal of this study was to assess the influence of lateral motion on stereothresholds for targets with various horizontal and vertical separations. A second goal was to use the results to yield an estimate of the extent of motion blur. Methods: The stereotargets consisted of 2 bright, 30-arc-min, thin vertical lines, separated vertically or horizontally by a gap of 5 to 50 min arc. Targets were presented centrally against a dark background for 200 ms, with horizontal velocities between 0 and 8 deg/s. The direction of motion (right vs. left) and the horizontal image disparity between the two lines 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. Results: Stereothresholds increase systematically when the velocity of target motion is greater than approximately 2 deg/s. At each velocity, the stereothresholds for horizontally and vertically separated targets are similar when the gap is large, but are higher for horizontally than vertically separated targets when the gap is small. The gap size at which the thresholds rise for horizontally separated targets increases in proportion to the target velocity, from approximately 5-8 min arc at 2 deg/s to 20-30 min arc at 8 deg/s. Conclusion: We assume that stereothresholds for horizontally separated targets increase when the gap size becomes small enough for motion smear from the leading line to overlap the trailing line and impair relative disparity processing. For the observers in our study, the extent of motion smear that impairs the thresholds for horizontally separated targets corresponds to a duration of approximately 40 - 60 ms.
This PDF is available to Subscribers Only