Prediction of illusory motion direction from eye tracking data
26.4030, Saturday, 16-May, 2:45 pm - 6:45 pm, Pavilion
Oliver Flynn1,2, Arthur Shapiro1,2; 1Department of Psychology, College of Arts and Sciences, American University, 2Center for Behavioral Neuroscience, American University
The perception of motion can be generated by modulating the contrast relationships among objects, backgrounds, and thin lines separating them (Gregory and Heard, 1983; Shapiro et al. 2005; and others). This motion can be called “illusory” since no elements in the image physically change location. Here we examine a variant of this type of motion to see the extent to which it produces eye movements and whether we can predict the direction of illusory motion by examining only the eye movement data. The stimulus consisted of a large mid-luminance colored diamond (visual angle 16 degrees) bordered by thin (0.07 deg) edges and surrounded by a background (19 deg). Both the edges and background modulated in luminance between light and dark at 2 Hz; due to differences in timing between these elements, the diamond appeared to move continously in one direction (up, down, left, or right, depending on condition) though the diamond itself did not change position (Flynn and Shapiro, 2012). An eye tracking camera (50 Hz, Cambridge Research Systems) mounted to a chin rest tracked the gaze of naive observers (n = 30) who were asked simply to “watch” the stimulus on a computer monitor. Each observer saw 50 3-second trials presented in ranomized blocks of 5 conditions (up, down, left, right, no motion). An analysis of the slope of the eye movements’change in position shows that observers’ eye movements drift in the direction of perceived motion. Additionally, an anylsis of the eye postion following saccades shows that observers’ gazes center around the leading edge of the stimulus in each motion condition. We conclude that illusions of motion appear to create reliable patterns of eye movements which resemble responses to real motion. Eye tracking data can be used to predict the direction of illusory motion perceived by the observer.