Autonomic Orienting and Adaptation Patterns to Repeated Sensory Stimuli in ASD

Background: Prevalence estimates of sensory processing differences in individuals with autism spectrum disorder (ASD) range as high as 96%. Furthermore, this difficulty perceiving and integrating sensory stimuli is frequently reported by parents and individuals with ASD as one of the largest barriers to functioning in day-to-day life. One method that is used to objectively examine sensory differences in ASD is measuring autonomic reactivity and regulation to sensory stimuli. The Sensory Challenge Protocol (SCP) is a paradigm that measures autonomic reactivity to a series of highly-standardized sensory stimuli from several domains. Results from past SCP studies in ASD have varied, finding both hyperresponsivity and hyporesponsivity to individual stimuli. However, existing studies have not examined within-domain autonomic responses across trials, which would provide important information about orientation and adaptation patterns to sensory stimuli.

Objectives: The current study measured sympathetic and parasympathetic responses to sensory stimuli using the SCP. Analyses specifically focused on reactivity patterns across trials within each sensory modality to better understand how individuals with ASD react to novel and repeated sensory stimuli.

Methods: Twenty-two adolescents with ASD (12-16 yrs) and 24 typically developing adolescents matched on age, gender, and IQ completed this study. Diagnoses were confirmed/ruled out using the Autism Diagnostic Observation Schedule and cognitive abilities were evaluated using the age-appropriate Wechsler assessment. Each participant completed the SCP, where their heart rate, respiration rate, and electrodermal activity were continuously collected during a standardized presentation of the following stimuli: an 84 dB pure tone, strobe light flashed at 10kHz, 80dB siren, wintergreen oil presented under the nose, and feather drawn across the jawline.

Results: Group x trial repeated measures analyses of variance were performed to examine overall cardiac reactivity and orienting responses. There was a significant group x trial interaction when considering all trials (p<.001), suggesting that individuals with ASD are overall less reactive to stimuli across trials. A separate analysis considering only baseline and the first two sensory trials in each domain also revealed a group x trial interaction (p<.001), suggesting a decreased or absent cardiac orienting response to novel stimuli in ASD. A priori analyses were repeated within each domain, as is commonly done in the SCP literature. These revealed significant group x trial interactions for responding across all trials on Tone, Wintergreen, and Feather (p’s <.05) and for orienting responses to initial stimuli for Tone, Wintergreen, and Siren (p’s <.05; Fig 1).

Conclusions: These results support autonomic hyporesponsivity to several sensory modalities in ASD. Specifically, the reduced cardiac orienting response found in the current study suggests that individuals with ASD may attend less readily to neutral sensory stimuli. This may impact information gleaned from their environment and may contribute to both a lower registration of sensory stimuli and, potentially, a defensive response to more aversive sensory stimuli. This study is the first to examine autonomic orienting responses in adolescents with ASD to several, carefully-presented sensory stimuli. The results help to clarify sensory dysregulation and perception in individuals with ASD, including how sensory differences may impact attentional processes.