The Developmental Trajectories of Multisensory Integration Differ Between Autistic and Typicaly Developed Individuals

Background:  Kanner’s original description of Autism is rife with descriptions of sensory impairments. Reports of sensory impairments have become widespread in the ASD literature including impairments in multisensory integration. A major factor influencing multisensory integration is the temporal relationship between sensory signals. One measure of the temporal aspect of multisensory integration is the temporal binding window (TBW), a probabilistic construct defining the interval of time within which auditory and a visual stimuli are perceptually bound. Complementing known temporal processing deficits, recent work shows that ASD individuals have an atypical TBW. It remains unclear how this difference between ASD and typically developed (TD) children develops.

Objectives:  We achieved three aims. We measured the developmental trajectory of the TBW in children with ASD, contrasted these findings with measures taken from a cohort of TD children, and provided a correlational link between the low-level measure of the TBW and a communication-specific measure of multisensory integration, the McGurk Effect.

Methods:  Participants- 24 ASD (6-18yo) and 40 TD children matched for age, IQ, and visual and auditory acuity. To measure the TBW, participants completed a simultaneity judgment task.  Flashes of light and auditory beeps were presented at varying stimulus onset asynchronies from audio-first 500ms (AV) to visual-first 500ms (VA). Additionally, participants completed a McGurk task in which they reported their perception to congruent /ba/ and /ga/ utterances and an illusory condition with an auditory /ba/ presented with a visual /ga/ (the McGurk stimulus).

Results:  Participants were binned into three age groups, 6-9, 10-13, and 14-18 (ASD n=8 each). In the youngest TD group, the TBW was wide and symmetrical, with a high proportion of stimuli perceived as synchronous even with long SOAs. The first developmental change in the TBW was a narrowing with the AV conditions, producing an asymmetrical TBW which reflects the temporal statistics of the natural environment where auditory input lags behind visual input due to differences in the speeds at which sound and light travel. The developmental change consisted of a general narrowing of the TBW. When compared with these TD results, ASD individuals showed wider and more symmetrical TBWs, an effect that became increasingly exaggerated with age, suggesting that these developmental changes had failed to occur across age groups. Finally, there was a significant difference in perception of the McGurk illusion, with ASD individuals reporting the illusion less than TD individuals. Importantly, this measure of speech integration was significantly correlated with individual’s TBW. Thus, the narrower the TBW, the greater the McGurk Effect, a proxy for integration of audiovisual speech.

Conclusions:  The development of temporal multisensory function was severely impaired in ASD relative to TD groups. The ASD group failed to develop an asymmetrical TBW that mirrors the natural statistical relationship between audiovisual stimuli in the environment. Despite the fact that the TBW was measured using highly reduced stimuli its width was significantly correlated with the perceptual fusion of complex speech stimuli, suggesting that this low-level deficit may cascade into deficits of higher-level cognitive processes such as speech perception.