Differences in the Multisensory Temporal Binding Windows of TD and ASD Individuals As a Function of Stimulus Complexity

Background:   

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder characterized by deficits in three core domains: communication, social behavior, and restricted/repetitive interests. Kanner also described sensory processing abnormalities in ASD individuals, and there have been a number of studies describing sensory deficits that span multiple modalities. While these sensory and multisensory deficits are interesting on their own, their connection to the core domains of autism dysfunction remains poorly defined.

Objectives:   

One area of critical importance for effective multisensory processing is the temporal structure of the stimuli that are being combined. Given the known changes in temporal function in autism, deficits in multisensory integration could occur if temporal processing mechanisms associated with combining cues are abnormal. An effective way to measure multisensory temporal function is the temporal binding window (TBW), the interval within which a stimulus pair is perceptually bound into a unified event. The goals of this project were to investigate and compare the multisensory TBWs of typically developed (TD) and ASD individuals as a function of stimulus complexity. Specific hypotheses include the expectation that individuals with ASD will have wider TBWs, and that more complex stimuli will be associated with wider TBWs. As a corollary of this, we expect as stimulus complexity increases, between-group differences in TBWs will increase as well.

Methods:   

40 TD and 24 ASD individuals (4-18 yo) completed a simultaneity judgment task to measure their TBWs using three levels of stimulus complexity: low-level visual and auditory stimuli (simple flashes and beeps), complex inanimate objects (handheld tools), and complex animate stimuli (speech). In all cases, the auditory and visual components were paired with parametrically varied levels of asynchrony, which varied from 0-500 ms in both auditory-leading and visual-leading configurations. The participants’ task was to report whether the events occurred simultaneously.

Results:   

We observed a main effect of group with ASD individuals having a wider TBW than TD individuals. That is, collapsing across levels of complexity, ASD individuals were more likely to report that asynchronous stimuli were synchronous compared to their TD counterparts. Also, we observed a main effect of stimulus complexity, with increasing stimulus complexity being associated with a wider TBW. Most importantly, a significant group by complexity interaction was measured, such that as the stimuli became more complex, ASD individuals’ TBWs widened to a greater extent than for TD individuals’. Additional analyses also revealed that the TBW of ASD individuals was more symmetrical than for TD individuals’.  

Conclusions:  

These findings demonstrate that ASD individuals have deficits in the temporal processing of multisensory stimuli, and this effect grows with increasing stimulus complexity. Such results have important implications for better understanding how (multi)sensory deficits contribute to the changes in higher-order domains such as communication and social interactions seen in ASD. Perhaps most importantly, the hierarchal nature of the changes seen here suggest important mechanistic links between the differing levels of multisensory integration and binding – links that could potentially be capitalized upon in the development of remediation tools and methods to improve sensory function in ASD.