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tion in social gaze may contribute to atypical language develop- ment in children with ASD. The tendency to avert gaze from the faces of others may lead to impoverished experience with speak- ing faces that could contribute to a reduction in detection of visual speech information. Moreover, a few studies (DeGelder et al., 1991; Massaro and Bosseler, 2003; Williams et al., 2004) sug- gest that children with ASD are less influenced by visual infor- mation for speech than are typically developing controls. Although these studies provide evidence that individuals with ASD are less influenced by some types of visible speech infor- mation, if perceivers fail to gaze at the speaker during produc- tion of speech it is impossible to determine whether perceivers with ASD actually integrate visual and auditory information less than controls do, or whether they are simply not gazing at the talking face. In particular, the tendency of individuals with ASD to avert gaze from the faces of others means that attenuated visu- al influence on heard speech in ASD may reflect reduced fixa- tion on the face of a speaker (Pelphrey et al., 2002). Alternatively, van der Geest and colleagues (2001a, 2001b, 2002) report simi- lar patterns of gaze to still images of faces and social scenes in ASD and control perceivers, suggesting that the reduction in AV speech integration is not due to a lack of gaze to the speaker’s face. Either the speaker’s face may not hold the same informa- tion for a perceiver with ASD as for a typical perceiver, with affected individuals showing difficulty in extracting phonetic information from the face, or may be due to a more fundamen- tal deficit in the capacity for AV integration.
Theories of perceptual deficits in autism
A number of theories of the perceptual deficits in indi- viduals with ASD can account for a weakness in AV integra- tion in this population. According to the central coherence theory (Frith and Happe, 1994) there is an impaired ability to perceive central coherence from individual features of a stim- ulus, such as a face (van der Geest, 2001a). The executive function theory (Ozonoff et al., 1991) explains autistic symp- tomatology as deficits in planning, inhibition, flexibility and search behaviors mediated by the frontal lobes. Problems with executive functioning may lead to atypical patterns of gaze and thus impoverished perceptual processing of visual information. An additional theoretical account, derived from the perceptual learning theory of Gibson (1969), proposes that lack of attention to a speaker’s face deprives a child with ASD of the experience necessary to develop typical sensitivi- ty to visual speech information. Experience with auditory speech has been found to be crucial in developing perceptu- al sensitivities in early development (Bergeson and Pisoni, 2004). Accordingly, there is evidence that the production of speech differs in blind individuals (Brieland, 1950; Lezak and Starbuck, 1964). Because of their tendency to avert gaze from others’ faces, individuals with ASD would have significantly limited access to visible speech information (Hobson et al., 1988; Volkmar and Mayes, 1990; Volkmar et al., 1989). Both seeing and listening to speech are essential for the develop- ment or maintenance of AV integration (Bergeson and
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