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Divya Nigam, Laysa Hedjar, Arthur Shapiro; Contrast generated illusory motion as a potential diagnostic tool. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4218.
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© ARVO (1962-2015); The Authors (2016-present)
The modulation of luminance contrast at an object’s edge can create the illusory appearance that the stationary object is moving continuously in a single direction (alturl.com/wysdn; Shapiro and Flynn, under review). Since the motion can occur when the edges are remarkably thin (<.1 min of visual angle), it is conceivable that continuous motion phenomenon can serve as a test of visual acuity and contrast gain sensitivity. Here we examine the feasibility of using this type of motion as a non-invasive diagnostic tool.
The stimuli consisted of physically stationary diamond shapes. By changing the temporal phase of the contrast at the diamond edges, the diamond can be made to appear to move up, right, left, down, inward, or outward. In Exp. 1, we measured psychometric functions for observer’s ability to report the correct direction as a function of contrast modulation, edge length (1, 2, 4, 8 min) and contrast gain (i.e., the luminance ratio between inner and outer edges). In exp 2, we measured threshold functions with the same variables but along a larger range of parametric manipulation. Participants were college age students, primarily enrolled at American University and had normal or optically corrected vision (Exp. 1, N=28, Exp. 2 N=63). We also measured CSF, Pelli-Robson and ETDRS acuity for all participants.
In exp. 1, psychometric functions (proportion of trials with correct i.d. of motion direction vs. contrast modulation) increased monotonically with contrast modulation; the psychometric functions were flatter for higher contrast gain. Exp 2 reported threshold function of contrast threshold v.s. edge length and v.s. contrast gain. Maximal sensitivity occurred for edges of 2 and 4 min widths and for low contrast gain (i.e. when modulating were nearly matched modulation contrast). Initial observation seem to suggest a correlation be threshold sensitivity on the diamond task and Pelli-Robson sensitivity.
The results of Exp. 1 and 2 show a proof of concept that the continuous motion phenomena may be useful for efficiently measuring acuity and contrast gain sensitivity in healthy observers, as well as indicating some of the crucial variable for such tests. Since individuals with higher Pelli-Robson values were able to complete our task, the results suggest that this type of configuration may be useful for clinical populations.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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