The effects of modality dominance and accuracy on motor reaction times to unimodal and bimodal stimuli

PURPOSE: Despite limited understanding of the underlying neural mechanisms involved in merging various sensory inputs and, in turn, the construction of a unified representation of the environment, it would appear that multisensory stimuli have a facilitating effect on information processing. It was the aim of this study to investigate multisensory processing using patterns of motor reaction times (MRTs) on a simple discrimination task as a means of categorizing groups of individuals. METHOD: Twenty-six adults were presented with temporally and spatially coincident unimodal (auditory or visual) and bimodal (auditory and visual) stimuli (100 ms duration), consisting of blue flashes as invalid (Vi) and red flashes as target (Vt) stimuli, and 500 Hz tones as invalid (Ai) and 600 Hz tones as target (At) stimuli. Overall, eight stimulus conditions were used: Ai, Vi, AiVi, At, Vt, AiVt, AtVi, and AtVt. Participants were required to press a button immediately in response to target stimuli: MRTs and response accuracy were recorded. Participants were subdivided into groups of visual dominant [Vis-Dom (n=16)] where MRT for Vt < At and auditory dominant [Aud-Dom, n=10] where MRT for At < Vt. RESULTS: Both Vis-Dom and Aud-Dom groups showed similar levels of facilitation for duel target bimodal stimuli (AtVt), i.e., MRTs were approximately 60 ms faster compared to unimodal stimuli and single target bimodal stimuli. Furthermore, MRTs to single target bimodal stimuli mirrored MRTs to unimodal stimuli, i.e., Vis-Dom and Aud-Dom participants' MRT were faster to AiVt and AtVi stimuli, respectively. An increase in speed, for all stimulus conditions, was also associated with high response accuracy. CONCLUSION: MRTs are partly dependent on an individual's dominant modality and performance accuracy. Nevertheless, maximum facilitation is achieved with duel target bimodal stimuli