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 highfunctioning 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 simpleand 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.A utism (1) is a severely debilitating developmental disorder, characterized by aberrant social skills, deficient language, abnormal attention, stereotyped repetitive behaviors, and often also mental retardation.One of the components of the social communication deficits in autism is peculiar attentional behavior. Individuals with autism show attentional preference to objects over people and a lack of a drive to communicate (2). Consistent with this, Swettenham et al. (3) found that 20-month-old infants with autistic features made significantly fewer attention shifts than did their controls from person to person and between a person and an object. They also spent more time looking at objects and less time looking at people. Further, 5-year-old children with autism oriented more poorly to social (both speech and nonspeech) than to nonsocial stimuli (4). Their impaired orienting to social stimuli correlated with the impairment of joint attention, one of the key features of autism.The neurofunctional deficits underlying this pattern of behavior are not yet understood, although recent research revealed disorders in many aspects of attentional behavior in autism. They include abnormalities in spontaneous looking (3), focused attention (5-11), and voluntary shifting of attention (12)(13)(14). Courchesne et al. (12) proposed that the majority of the attentional deficits observed in autism might be caused by a cerebellar dysfunction that slows down the adaptation of the neural systems to the const...

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In children, deviant sounds in an oddball paradigm elicit a mismatch negativity (MMN) indexing discrimination of sound change and late difference negativity (LDN) with unknown functional significance. Salient sounds elicit an ERP index if orienting, P3a, and a late negative component, Nc. We compared children's responses elicited by moderate sound changes and novel sounds to examine the relationships between MMN and LDN, and LDN and Nc. Two components of the Nc, the Nc1 and Nc2, were identified. The scalp topography of LDN differed from those of the MMN and Nc1. Children's early P3a appeared mature but late P3a lacked frontal predominance. The findings suggested that LDN is not linked with either the sensory or attentional processing. It might reflect cognitive, albeit preattentive, processing of sound change. The Nc1 appears to reflect cognitive attentive processing of salient stimuli and the Nc2 might reflect reorienting after distraction.