Early, low-level auditory-somatosensory multisensory interactions impact reaction time speed

Holger F Sperdin

doi:10.3389/neuro.07.002.2009

Abstract

Several lines of research have documented early-latency non-linear response interactions between audition and touch in humans and non-human primates. That these effects have been obtained under anesthesia, passive stimulation, as well as speeded reaction time tasks would suggest that some multisensory effects are not directly influencing behavioral outcome. We investigated whether the initial non-linear neural response interactions have a direct bearing on the speed of reaction times. Electrical neuroimaging analyses were applied to event-related potentials in response to auditory, somatosensory, or simultaneous auditory–somatosensory multisensory stimulation that were in turn averaged according to trials leading to fast and slow reaction times (using a median split of individual subject data for each experimental condition). Responses to multisensory stimulus pairs were contrasted with each unisensory response as well as summed responses from the constituent unisensory conditions. Behavioral analyses indicated that neural response interactions were only implicated in the case of trials producing fast reaction times, as evidenced by facilitation in excess of probability summation. In agreement, supra-additive non-linear neural response interactions between multisensory and the sum of the constituent unisensory stimuli were evident over the 40–84 ms post-stimulus period only when reaction times were fast, whereas subsequent effects (86–128 ms) were observed independently of reaction time speed. Distributed source estimations further revealed that these earlier effects followed from supra-additive modulation of activity within posterior superior temporal cortices. These results indicate the behavioral relevance of early multisensory phenomena.

Highlights

One consistency is that convergence and non-linear interactions occur within the initial temporal stages of cortical processing and involve belt regions of auditory cortex adjacent to primary cortices
BEHAVIORAL RESULTS On average, subjects detected 99.8 ± 0.4% of auditory right stimuli, 99.9 ± 1.3% of somatosensory right stimuli, and 99.7 ± 0.5% of multisensory right stimulus pairs
ELECTROPHYSIOLOGIC RESULTS Visual inspection of the group-averaged event-related potential (ERP) across conditions at an exemplar left-lateralized central electrode site (C3 according to the 10–10 nomenclature; American Electroencephalographic Society, 1994) suggests that over the ∼40–80 ms post-stimulus period responses to multisensory stimuli were of higher amplitude than those to all other conditions when RTs were subsequently fast

Summary

Introduction

Multisensory interactions have been documented across the animal kingdom as well as across varying pairs of sensory modalities and can serve to enhance perceptual abilities and response speed (Calvert et al, 2004; Driver and Spence, 2004; Stein and Meredith, 1993; Stein and Stanford, 2008; Welch and Warren, 1980) as well as learning (Lehmann and Murray, 2005; Murray et al, 2004, 2005a; Shams and Seitz, 2008). It is worth noting that these kinds of effects do not preclude additional effects at later stages and within higher-order brain regions (Driver and Noesselt, 2008) Despite this shift in how sensory processing is considered to be organized (Foxe and Schroeder, 2005; Ghazanfar and Schroeder, 2006; Wallace et al, 2004), a challenge remains regarding whether there are direct links between early, low-level multisensory interactions and behavioral indices of multisensory processing. One consistency is that convergence and non-linear interactions occur within the initial temporal stages of cortical processing (i.e., within 50–100 ms post-stimulus) and involve belt regions of auditory cortex adjacent to primary cortices

Methods

Results

Conclusion