Electrophysiological Assays of Multisensory Integration and Sensory Processing in Autism Spectrum Disorders
The development of ordered interactions among inputs to the different sensory systems is a necessary component of normal functioning and plays a fundamental role in our ability to successfully navigate the environment. Examples of multisensory influences on normal perception are manifold. For example, seeing someone speak can have profound effects on what is heard, and the perceived location of a sound is affected by the location of a co-occurring visual event. It has been proposed that failure to develop normal integration of sensory inputs is at the root of some childhood neuro-behavioral disorders, a notion that has been especially applied to autism. This notion led to the formulation of the Sensory Integration Theory in the late 70’s, a theory that has attracted a large following over the intervening years.
Psychometric tests and questionnaires indicate profound differences in sensory processing in individuals with autism. However, the neural underpinnings of these sensory processing differences remain elusive. One promising line of research suggests that differences in connectivity may be involved. It has been argued that in autism, perhaps as a consequence of reduced long-range connectivity, typical perception and cognition are disrupted when information must be integrated across sensory and cognitive domains. A breakdown in long-range connectivity would of course lead to impoverished integration of sensory information across modalities.
1) To use objective neural and behavioral metrics of sensory processing and multisensory integration (MSI), in order to probe the integrity of multisensory integration processes in ASD.
2) To develop biomarkers that can be used to assay normalization of function due to treatment.
High-density electrophysiological scalp recordings served to measure the brains response to unisensory and multisensory stimuli (basic visual, auditory, and somatosensory stimuli presented alone or simultaneously). Parallel behavioral reaction-time measures assessed perceptual enhancement due to multisensory stimulation. In an additional, purely behavioral paradigm, the consequence of impaired MSI for speech processing was examined. Here participants identified spoken words-in-noise that were sometimes accompanied by videos of the speaker saying the word. Improved performance on the auditory-plus-video condition compared to the auditory-alone condition indexed MSI.
Basic unisensory processing was relatively intact in ASD, especially for somatosensory and visual stimulation. In contrast, integration of audiovisual multisensory inputs was significantly impaired in this group, as evinced by both neurophysiological and behavioral measures. The audiovisual speech-in-noise task further revealed profound MSI deficits in children with autism that impacted their ability to discern words in a noisy environment.
The ability to integrate multiple sensory cues incurs major advantage to decoding the social and communicative milieu. The impaired MSI that we observe in children with an ASD puts them at significant disadvantage in such complex situations where a fine weighting of multisensory cues is required. The protracted development of MSI offers a window of opportunity for intervention to remediate MSI. Here we present measures of MSI that can be used to assess the impact of interventions on these fundamental processes.