Modeling spatial effects in visual-tactile saccadic reaction time.

Saccadic reaction time (SRT) to visual targets tends to be shorter when nonvisual stimuli are presented in close temporal or spatial proximity, even when subjects are instructed to ignore the accessory input. Here, we investigate visual-tactile interaction effects on SRT under varying spatial configurations. SRT to bimodal stimuli was reduced by up to 30 msec, in comparison with responses to unimodal visual targets. In contrast to previous findings, the amount of multisensory facilitation did not decrease with increases in the physical distance between the target and the nontarget but depended on (1) whether the target and the nontarget were presented in the same hemifield (ipsilateral) or in different hemifields (contralateral), (2) the eccentricity of the stimuli, and (3) the frequency of the vibrotactile nontarget. The time-window-of-integration (TWIN) model for SRT (Colonius & Diederich, 2004) is shown to yield an explicit characterization of the observed multisensory spatial interaction effects through the removal of the peripheral-processing effects of stimulus location and tactile frequency.