Integration of visual and tactile stimuli: top-down influences require time

In a visuotactile congruency task, a distracting flash of light presented near a tactile target can influence speeded judgments of tactile location. Localization of the tactile target is more rapid when the elevation of the visual distractor is congruent with the tactile stimulus than when it is incongruent. The goal of the present study was to examine the degree of control that can be exerted on the process proposed to integrate the visual and tactile stimuli. To this end, the proportion of spatially congruent items was manipulated across blocks of trials. A robust congruency effect was observed across three experiments. There was no effect of proportion congruency (varied between 75 and 11% congruent) when the visual event was presented only 30 ms prior to the tactile event. When this lead-time was increased to 100 ms there was a significant increase in the congruency effect, for errors, in the high proportion congruent conditions (experiment 3). We conclude that with sufficient lead-time, top-down influence can be exerted in this task, however, when presented at near simultaneity, visuotactile integration is independent of top-down effects.