Contrast-Generated Illusory Motion as a Potential Diagnostic Tool

The modulation of luminance contrast at an object’s edge can create the illusory appearance that a stationary object is moving continuously in a single direction (Shapiro and Flynn, submitted). Since this motion can occur when the edges are extremely narrow less than minimum of visual angle), it is conceivable that a continuous motion phenomenon can serve as a test of visual acuity and contrast sensitivity. We have examined the feasibility of using this form of motion as a non-invasive tool. The stimuli (Motion Diamond Stimulus-MDS) consists of physically stationary diamond shapes. By altering the temporal phase of the contrast of the diamond edges, the diamonds can appear to move upward, downward, left, down, outward, or inward. Experiment 1 measured psychometric functions for observer’s ability to report correct directions as a function, while Experiment 2 measured threshold functions with a larger range of parametric manipulation. These experiments depicted psychometric functions increasing monotonically with contrast modulation with functions being flatter for higher contrast gain. Maximal sensitivity occurred at edge length 4 (width of edge 4 min of visual angle) corroborating with past literature. Initial observations also indicate a correlation of threshold sensitivity on the MDS and clinical (Pelli Robson) sensitivity values.