Two eyes are identical to one: Three-dimensional motor tracking of visual targets
53.4098, Tuesday, 19-May, 8:30 am - 12:30 pm, Pavilion
Kathryn Bonnen1,2, Alexander Huk1,2,3, Lawrence Cormack1,2,3; 1Institute for Neuroscience, The University of Texas at Austin, 2Center for Perceptual Systems, The University of Texas at Austin, 3Department of Psychology, The University of Texas at Austin
The threshold for detecting stereoscopic motion is notably higher than that for detecting the equivalent fronto-parallel motion. Thus, for small excursions, an apparently stationary line can easily be seen as moving by simply closing one eye – two eyes being less sensitive than one (Tyler, 1971). Here, we used a 3D tracking paradigm to examine motion perception with a continuous motor task. Observers used a cursor to track a target as it moved in a 3D Gaussian random walk. In the main experiment, each eye saw a veridical 2D projection of a square target and cursor moving in 3D. A Leap Motion controller was used to move the cursor by simply pointing at the target location. The controller was calibrated such that there was a one-to-one mapping between finger movement and simulated cursor movement. Tracking data were analyzed by computing the cross-correlograms (CCGs) between the target and cursor velocities for each of the three cardinal motion directions, and assessing the lag, peak correlation, and width of the CCGs. Responses to the depth component of the motion were markedly weaker and more sluggish than responses to the fronto-parallel directions. Further experiments revealed that these depth responses were identical when either only horizontal disparity information was available or when a disparity-only target was viewed monocularly. Our primary finding was that depth tracking is worse than fronto-parallel tracking, but this was simply due to the much smaller amplitudes of projected fronto-parallel motion that motion-in-depth produces. We did not find evidence for the stereo-motion suppression observed with traditional psychophysics, nor did we find a need to invoke a specific disparity processing mechanism. Rather, continuous tracking behavior is parsimoniously explained by reliance on the 2D projections of 3D motion.