Purchase this article with an account.
Harold E. Bedell, Thao C. Lien, Jianliang Tong, Patricia M. Cisarik, Saumil S. Patel; Motion sensitivity and fixation variability along individual meridians. Journal of Vision 2005;5(8):137. doi: 10.1167/5.8.137.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose. Murakami (VR, 2004) reported a relationship between motion sensitivity and the variability of fixational eye movements in normal observers and concluded that retinal image motion during fixation is discounted perceptually. In this study, we investigated whether sensitivity to motion along specific meridians is limited by the variability of fixation in the corresponding meridian. Methods. Random-dot motion was presented in an array of 8 blurred patches, spaced equally around an imaginary circle with a 10-deg diameter. The observer fixated monocularly at the center of the circle. On each trial, all of the random dots in each patch translated for 500 ms in a common direction: right, left, up, down, clockwise, or anti-clockwise. Motion thresholds were defined as the velocity of horizontal, vertical, or rotary motion that yielded 50% correct judgments. Variability of fixation was specified as the SDs of horizontal, vertical, and torsional eye velocity for 168 half-sec samples, measured using a search coil. Results. In agreement with Murakami, the average thresholds for horizontal and vertical motion in 11 normal subjects correlated significantly (r = 0.67, p = 0.025) with the average SDs of horizontal and vertical eye velocity. However, no correlation existed between motion thresholds and the SDs of eye velocity when the results were not averaged across meridians (r = 0.019). Further, no relationship existed within subjects between motion thresholds and the SDs of eye velocity in corresponding meridians. Conclusions. One explanation of our results is that the visual system discounts retinal image motion produced by normal fixational eye movements, based on the average variability of eye velocity across meridians. If so, then discounting the retinal image motion from eye movements cannot account for the anisotropic motion thresholds in congenital nystagmus, unless the discounting process operates differently in subjects with meridionally impaired fixation.
This PDF is available to Subscribers Only