Mair, KR; (2013) Speech perception in autism spectrum disorder: susceptibility to masking and interference. Doctoral thesis , UCL (University College London).

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Abstract

High-functioning adults with autism spectrum disorder (ASD) frequently report difficulties with speech perception in background noise, which cannot be explained simply by an impairment in peripheral hearing or structural language ability. In spite of the apparent prevalence of this problem, however, only a handful of studies so far have evaluated speech reception thresholds (SRTs) in this group under controlled conditions, and then only with a limited range of (mainly non-speech) masking sounds. Results have indicated relatively minor deficits in some types of background noise, but not in others: at most, ASD listeners have required the signal-to-noise ratio to be around 3 dB more favourable than matched controls to report speech with 50% accuracy. This thesis describes a series of sentence in noise tasks, in which SRTs were measured for a far wider range of speech and non-speech masking sounds than before. Two groups of normally-hearing young adult participants completed the experiments: one group who had received a clinical diagnosis of Asperger's syndrome, and the other a group of neurotypical controls matched for age, verbal IQ and non-verbal IQ. The key results were that a substantial proportion of the ASD group ('ASD+') performed consistently within the normal range across the majority of target sentence types and masking conditions, whereas around half ('ASD-') tended to perform significantly poorly. When these two subgroups' results were analysed separately, it became clear that the ASD- listeners showed much greater deficits in SRT with speech maskers than with non-speech. Moreover, they were particularly affected by masking speech with similar perceptual and linguistic features to the target material, showing deficits of up to 15 dB in these conditions. This pattern of performance is strongly suggestive of an impairment in auditory stream segregation and/or selective attention to speech in a subset of high-functioning adults with ASD.

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