ELECTROPHYSIOLOGICAL AND BEHAVIORAL MEASURES OF TACTILE AND AUDITORY PROCESSING IN CHILDREN WITH AUTISM SPECTRUM DISORDER
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Touch plays a key role in facilitating social communication and is often presented in conjunction with auditory stimuli such as speech. Individuals with autism spectrum disorder (ASD) frequently show atypical behavioral responsivity to both tactile and auditory stimuli, which is associated with increased ASD symptomatology. However, as discussed throughout Chapter 1, the neural mechanisms associated with responsivity to tactile and auditory stimuli in ASD are not fully understood. For example, some have argued that differences in responding to tactile and auditory stimuli may be attributed to sensory and perceptual factors, whereas others suggest that these differences could be related to atypicalities in allocation of attention to incoming stimuli. In Chapter 2, I address these competing hypotheses by examining early and late ERP components (indicative of perceptual and attentional processing respectively) in response to tactile and auditory stimuli. Next, despite the evidence suggesting that touch plays a role in modulating attention in typical development (TD), it is unclear whether touch cues affect the response of the phasic alerting network – a subcomponent of attention – in ASD and TD, and whether the alerting response may be atypical in children with ASD. In Chapter 3, I address this gap in the literature by examining whether tactile cues presented at different intervals before auditory targets facilitate reaction times differently in children with ASD and TD. Lastly, because prior research has shown associations between sensory and attentional processes and ASD symptomatology, in Chapters 2 and 3, I examine the associations of neural and behavioral indices of tactile and auditory processing with ASD symptomatology and language skills in children with ASD and TD.
In Chapter 2, I show that children in both the ASD and TD groups do not exhibit differences in both early and later neurological responses to tactile and auditory stimuli, suggesting that under certain experimentally-controlled conditions, behavioral differences to tactile and auditory stimuli may not be attributable to atypicalities in perceiving or attending to the incoming sensory input. However, neural responsivity to tactile and auditory stimuli is linked with sensory responsivity and social skills in all children. Specifically, reduced early contralateral activation to tactile stimuli is related to increased tactile symptoms, and reduced early amplitudes to auditory oddball stimuli are associated with impairments in reciprocal social communication in children with ASD as well as when examined across all children, and greater tendency of overall sensory hyper-reactivity. Additionally, in the TD group, greater later amplitudes to touch and auditory oddball stimuli are related to differences in reciprocal social communication and sensory reactivity respectively, indicating that patterns of allocation of attention may be related to ASD-like traits in typical development. Lastly, there is an association between greater sensitivity to changes to a stream of auditory stimuli and expressive language skills in all children. These results suggest that, although there are no group differences between neurological responses to tactile and auditory stimuli in ASD and TD, individual neural differences may be related to sensory and socio-communicative skills in all children.
In Chapter 3, I show that although children with ASD responded more slowly than children with TD, both groups displayed faster reaction times as a result of tactile cues before auditory targets, suggesting equivalent phasic alerting in response to tactile stimuli. Longer intervals between cues and targets benefitted children in both groups resulting in faster reaction times. Contrary to my hypotheses, touch-related behavioral facilitation was not associated with ASD symptomatology and language skills.Taken together, the results of these studies suggest that, at least in certain contexts and with certain cues, children with ASD may show typical neurological processing in response to tactile and auditory stimuli, and that touch may facilitate the response of the alerting network similarly in ASD and TD. Therefore, everyday behavioral differences in response to tactile and auditory stimuli may be related to the specific nature of the stimuli as well as social contexts in which such stimuli are more likely to be encountered. Differences between processing rich and dynamic sensory stimuli experienced in the outside world vs experimentally-controlled sensory stimuli presented in the laboratory settings are discussed in Chapter 4. Additionally, I argue that individual responses expected in social vs non-social experimental settings may affect neural and behavioral responses in individuals with ASD. Finally, future research directions are discussed.