Do Sensory Processing Deficits Impact on Speech Encoding in ASD? Evidence from an Experimental Study of Intellectually High-Functioning Adults

Background: Whilst sensory disturbance is well documented in ASD, relatively little is known about the impact of atypical auditory processing on speech perception in intellectually high-functioning adults.  Previous research carried out with children with ASD has revealed enhanced sensitivity to the psychoacoustic qualities of speech but the extent that this is characteristic in adults has yet to be investigated. 

Objectives: To determine whether the spectral and temporal characteristics of speech influence recall of grammatically simple and complex sentences.

Methods: 50 sentences with either subordinate or non-subordinate clauses were utilized to assess the effect of grammatical complexity on sentence recall. In order to isolate perceptual as well as higher-order speech processing deficits, speed and pitch manipulations were carried out on the stimuli. 19 HFA adults and intelligence and age matched typically-developing controls participated in the study. ANOVAs were conducted to analyse the main effects of grammatical complexity, perceptual manipulation, and group.  Correlational analyses were then used to examine the extent to which sensory processing abnormalities and scores on standardised measures of language and communication were associated with reduced performance in response to perceptual and higher-order changes in the experimental stimuli.

Results: Results showed that whilst the ASD group obtained significantly lower scores than controls on standardised measures of language and communication, the effects of grammatical complexity on sentence recall did not differ across groups. Whilst sensory abnormalities across all modalities including the auditory domain were observed in the ASD group, reduced sentence recall, in response to speed manipulations, was not significantly different to that of controls.

Conclusions: We conclude that memory for speech is unaffected by grammatical complexity in ASD and that this effect is robust enough to be sustained when speech stimuli are distorted. The associations between sensory processing abnormalities, level of symptom severity and speech perception will be further discussed