Asymmetric interaction between motion and stereopsis revealed by concurrent adaptation

Abstract

Although joint processing of motion and stereopsis has been suggested by contingent aftereffects, the reciprocal nature of encoding these two features has not been systematically studied. To investigate mutual influences between motion and stereopsis, we measured the processing of these features in parallel under ‘concurrent’ adaptation. In experiment 1, the adapting stimulus consisted of 110 random dots moving coherently in a single direction (left or right) at a single disparity (crossed or uncrossed 0.2°). Before and after adaptation, observers reported which one of the two sequentially presented intervals contained coherent motion or stereo signal. For motion detection, one of the intervals contained only ‘noise’ dots that were moving in random directions and the other contained both ‘noise’ and ‘signal’ dots that coherently moved either in leftward or rightward direction. All dots were at crossed or uncrossed disparity of 0.2°. For stereo detection, ‘noise’ dots were randomly dispersed over ±0.3° and ‘signal’ dots were at either crossed or uncrossed 0.2°. All dots were moving either leftward or rightward. We found a strong asymmetry between motion and stereopsis. The detection of disparity signal after adaptation was more impaired when the tester was moving in the adapted direction than in the non-adapted direction. In contrast, the test disparity hardly affected the detection of coherent motion, which is in contrary with the findings reported in contingent aftereffects. In experiment 2, we employed an adaptor that contained two groups of dots that were moving oppositely at crossed and uncrossed disparities, respectively, as in the previous studies of contingent aftereffects. Using the same testers as those in experiment 1, we observed considerable disparity dependency in motion detection. The results urge the reinterpretation of previously reported contingent aftereffects and imply an asymmetry between neural mechanisms devoted to processing motion and stereopsis in human visual cortex.