THE TIMING OF COLOR AND LOCATION PROCESSING IN THE MOTOR CONTEXT

In this study, the use of color and location as stimulus attributes ma nipulated during a simple action was aimed at comparing how dorsal (lo cation) and ventral (color) features are integrated in action and the timing of their processing. Eighteen subjects were presented with a gr een dot on a computer screen, which they were required to point at and touch. In 20% of the trials, the location or the color of the target was altered at the onset of movement to this stimulus, requiring the p articipant to modify the initially programmed response according to sp ecific motor instructions. In the 'location-go' group, the target chan ged in location and participants were instructed to reach the displace d stimulus by correcting their ongoing movement. In the 'location-stop ' and 'color-stop' groups, subjects were instructed to interrupt their movement when the target changed location or color, respectively. Res ults showed that the latency of the first responses to the perturbatio n clearly depended on the stimulus attribute and not on the motor inst ruction tested: the response to color change was obtained about 80 ms later than both conditions involving location change. It is concluded that: (1) color processing is slower than location processing, and (2) the first reactions to the location change occur after the same delay irrespective of the response required from the subject.