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Divya Nigam, Arthur G. Shapiro; Contrast generated illusory motion: a parametric investigation of edge-width and contrast ratio. Journal of Vision 2017;17(15):47. doi: 10.1167/17.15.47.
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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. Here we show how this effect can be used as a non-invasive diagnostic tool to test visual acuity and contrast gain sensitivity. The stimuli consist of five physically stationary mid-luminance diamond shapes, each surrounded by a circular field. The luminance of the diamonds' edges and the surround modulate at 2 Hz. By altering the temporal phase of the edge modulation relative to the surround modulation, the diamonds can be made to move up, right, left, down, inward, or outward. We measured psychometric functions for observers' (college age students enrolled at American University, normal or corrected vision) ability to report the correct direction as a function contrast modulation, edge length and contrast gain (luminance ratio between inner and outer edges). We then measured threshold functions with the same variables were measured with a larger range of parametric manipulation. PelliRobson, ETDRS acuity and CSF measures were taken in all participants. The psychometric functions (proportion of trials with correct i.d. of motion direction vs. contrast modulation) increased monotonically with contrast modulation. Observers were most sensitive to edges at 4 min of visual angle. 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.
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