Absence of Motor Coactivation in Bimodal Divided Attention: Two Case Studies

When attention is divided across vision and hearing, participants typically respond faster when a visual and an auditory target are presented together as compared to when only one of the visual or auditory targets is presented alone. Coactive models of divided attention account for this so-called bimodal advantage by positing a brain architecture whereby the neural activity inspired independently by concurrently presented auditory and visual targets is first processed in parallel and then pooled into a common resource. However, it remains unclear whether such pooling of activation occurs in the perceptual/cognitive processing of targets or later in the physical (motor) execution of the response. Here, two empirical case studies are reported examining the locus of coactivation in bimodal divided attention by way of planned theoretically driven analysis of each individual’s response times (RTs) and peak response forces (pRFs) to weak and energetic pulses of sound and light. Individually for both participants, RT was found to decrease with increased stimulus intensity and to be faster when both auditory and visual targets were presented together than the fastest RTs obtained when either target was presented alone. In contrast, pRF remained unaffected by either experimental manipulation. The results support current theoretical accounts of the bimodal advantage which posit an early or central locus of coactivation, with a subsequent motor component that ensues in a relatively invariant manner