Mapping the Developmental Trajectory of Audio-Visual Integration Using High-Density Electrophysiology

Background:  Many individuals with autism spectrum disorders (ASD) find aspects of the “typical” sensory environment overwhelming.  One explanation put forth is that individuals with ASD do not integrate inputs from the various sensory systems (sight, touch, hearing) into meaningful and manageable units, and that this contributes to sensory sensitivities among other perceptual and cognitive sequelae. However there is little empirical research to date that directly tests the integrity of multisensory processing.
Objectives: The overarching goal is to establish whether multisensory deficits are present in children with ASD and to characterize the neurophysiological basis of these deficits. Here we use high-density electrical mapping to map the developmental trajectory of basic auditory-visual integration in typically developing children from ages 6 to 17 (N=51).  This will serve as a baseline against which to compare multisensory integration in individuals with autism.  Data from a group of children with ASD from a more restricted age-range is also examined.
Methods: High-density electrophysiological recordings were made while participants engaged in a simple reaction-time task in which they responded to the occurrence of an auditory, visual, or auditory-visual stimulus.  The three stimulus types were presented in an unpredictable randomized order. To assess multisensory interactions, electrophysiological responses (ERPs) to the auditory-alone condition and the visual-alone condition were summed for each participant and compared to the response to the stimulus condition in which the stimuli were presented together (sum versus simultaneous).  Data from typically developing children were divided into three age groups to begin to map the developmental trajectory of basic multisensory integration for auditory and visual stimuli.  Data from a smaller group of children with ASD were compared to age and IQ matched controls.
Results: Analysis of the data from the typically developing children indicates that there are developmental changes in how the brain integrates simple auditory and visual inputs over the course of childhood.  Earlier multisensory interactions were seen in the younger cohorts of children compared to the oldest cohort of children (~100 ms post stimulus onset), whereas later multisensory interactions were more prominent in the older groups.  Behaviorally, multisensory integration was signified by violation of the race model.  Race model violation was seen to a greater extent in older children compared to younger children, with no evidence of race model violation in the youngest group.  Preliminary analysis of data from the ASD group suggests differences in auditory-visual integration compared to an age and IQ matched group of TD children.
Conclusions: Mapping the developmental trajectory of multisensory integration is essential to testing the integrity of these processes in clinical groups such as ASD.  Here we use electrophysiology to show that multisensory integration is modified over the course of childhood.  Behavioral data from our laboratory on higher order multisensory integration indicate that such malleability is absolutely key to the optimized use of multisensory inputs in perception.  Our findings also point to clear differences between multisensory integration in TD children and children with ASD.  Continuing work in our laboratory will determine the developmental course of simple auditory-visual integration in this group.