Speech-sound-selective auditory impairment in children with autism: they can perceive but do not attend

Abstract

In autism, severe abnormalities in social behavior coexist with aberrant attention and deficient language. In the attentional domain, attention to people and socially relevant stimuli is impaired the most. Because socially meaningful stimulus events are physically complex, a deficiency in sensory processing of complex stimuli has been suggested to contribute to aberrant attention and language in autism. This study used event-related brain potentials (ERP) to examine the sensory and early attentional processing of sounds of different complexity in high-functioning children with autism. Acoustically matched simple tones, complex tones, and vowels were presented in separate oddball sequences, in which a repetitive "standard" sound was occasionally replaced by an infrequent "deviant" sound differing from the standard in frequency (by 10%). In addition to sensory responses, deviant sounds elicited an ERP index of automatic sound-change discrimination, the mismatch negativity, and an ERP index of attentional orienting, the P3a. The sensory sound processing was intact in the high-functioning children with autism and was not affected by sound complexity or "speechness." In contrast, their involuntary orienting was affected by stimulus nature. It was normal to both simple- and complex-tone changes but was entirely abolished by vowel changes. These results demonstrate that, first, auditory orienting deficits in autism cannot be explained by sensory deficits and, second, that orienting deficit in autism might be speech-sound specific.

Figure 1

The auditory sensory ERPs elicited by the repetitive “standard” sounds in the children with autism and in the controls in the vowel (Top), complex-tone (Middle), and simple-tone (Bottom) conditions. There was a tendency for the P1 peak to be smaller in children with autism as compared with that of the controls.

Figure 2

The deviant-minus-standard difference waves in children with autism and in the controls, obtained in the vowel (Top), complex-tone (Middle), and simple-tone (Bottom) conditions. There were no significant group differences in the MMN amplitude. In contrast, the P3a response was absent in children with autism, but in the vowel condition only.