Apparent motion of double drift target originates from physical location at short delays but from closer to perceived location at longer delays

Abstract

In the double-drift stimulus a gabor moves in one direction in the periphery while its internal texture moves in the orthogonal direction. In this case, the perceived trajectory deviates from its physical trajectory by as much as 45° or more (Tse & Hsieh, 2006; Shapiro et al, 2010; Kwon et al, 2015; Lisi & Cavanagh 2015). We tested the effective location of the gabor at the trajectory endpoint by presenting a brief test and having observers judge the the perceived direction of the apparent motion from the point of gabor offset to the point of test onset. On each trial, a double drift gabor moved upward along a 1 dva linear path tilted 22.5° to the left or right of vertical at 8 dva in the periphery. The internal motion of the gabor was set to make the perceived path appear tilted 22.5° on the other side of vertical. At the end of the trajectory, the gabor disappeared and after a random interval of 0–350 ms, a test gabor with no internal drift appeared for 200 ms 1.5 dva vertically above the start point of the initial path, so centered horizontally midway between the physical and illusory endpoints. At short intervals, the apparent motion appeared to originate from the physical location of the endpoint, but at longer intervals, it appeared to originate from about midway between the physical and perceived locations. This result is in agreement with previous reports that immediate saccades go to the physical location of double-drift targets whereas delayed saccades go more to their perceived locations (Massendari, Lisi, Collins, & Cavanagh, 2018; Ueda, Abekawa, & Gomi, 2018).

Acknowledgement: NSF EPSCoR Award #1632738