Abstract
We used targets in apparent motion to study the spatio-temporal integration of color and motion features. In our display, 10 stimulus patches of colored dots were arrayed in a circle around fixation. The color of the dots in each patch alternated rapidly between red and green and the dots within each patch were also moving and they changed their direction from inward to outward (although the patch itself did not move) in synchrony with the color changes. Participants reported the color or the motion of the patch that was surrounded by a ring. In the stationary attention condition, the ring was flashed on and off at a fixed location, surrounding the target color or motion on every other frame. In the moving attention condition, the ring jumped from one location to the adjacent one on each frame. Because adjacent locations alternated in counterphase, the moving ring surrounded the same target color or motion on each frame and generated the percept of a single target in apparent motion, jumping from location to location around the array. Performance for reporting the individual feature (motion or color) was greatly enhanced in the moving attention case and performance also accumulated across locations, suggesting nonretinotopic integration. To determine the spatial and temporal range over which the integration occurred, we introduced gaps in the stimulus array by deleting every second location. Now the moving ring encircled the target feature only at each second location and the intervening locations were blank. Despite the spatial and temporal gaps that this introduced, there was little loss in performance when reporting color. However, there was a significant loss in performance for reporting the motion. These results suggest that the spatial and temporal ranges for integrating color and motion are different.
Wei-Lun Chou is supported by Graduate Students Study Abroad Program of the National Science Council, R.O.C. (Taiwan).