Auditory Processing in Autism Spectrum Disorder: Probing Individual Differences with Behavioral, Audiological, and Neurophysiological Measures

Background:

Auditory processing differences including hyper- or hyposensitivity to sounds as well as aversions or unusual interests in sounds are commonly reported by individuals with autism spectrum disorder (ASD). Furthermore, past studies of auditory perception have revealed difficulty listening under noisy conditions, reduced responsiveness to speech, impaired prosody and voice emotion perception, and enhanced pitch perception in individuals with ASD. Atypical physiological responses have also been documented, including otoacoustic emissions (OAE), auditory brainstem responses (ABR), as well as cortical event-related potentials. However, the findings reported are variable across studies and are dependent on the stimuli presented and the age of participants. Thus, the etiology of auditory processing differences in ASD is currently not well understood. One likely contributor to these inconsistent past findings is the heterogeneity of ASD itself.

Objectives:

This pilot study investigates individual differences in auditory processing by combining behavioral, audiological, and neurophysiological measures to create Auditory Processing Profiles for each participant. We hypothesize that this assay of auditory function, in contrast to previous measures of a single neurophysiological response, will reveal replicable patterns of neurophysiological differences across individuals with ASD.

Methods:

Twenty-four participants age 21-22 years (ASD n=12; TD n=12) were recruited from a larger longitudinal study conducted at the University of Washington Autism Center and the community. Speech perception, otoacoustic emissions, electrophysiological responses, and standardized assessments of cognition, language, and adaptive function were conducted. The Autism Diagnostic Observation Scale was administered to confirm diagnosis. Speech perception was assessed by estimating target-to-masker ratios at 50% correct for speech targets (0° azimuth) presented with two spatially separated (±45° azimuth) simultaneous speech maskers. The electrophysiological battery used to characterize the transmission and representation of sound included: (1) a click-evoked supra-threshold auditory brainstem response, (2) an envelope following response (EFR) recorded to a 400-ms-long 4 kHz pure tone carrier amplitude modulated at 100 Hz at two modulations depths (0 and -6 dB) and (3) a binaural evoked interaural phase difference (IPD) threshold.

Results:

Preliminary analyses revealed that as a group, ASD participants demonstrated difficulty with speech perception in a multi-talker situation with poorer thresholds than controls. However, individuals with ASD did not show the same deficits on electrophysiological measures. Some individuals with ASD showed reduced EFRs and poorer IPD thresholds while other individuals showed EFRs and IPD thresholds comparable to controls.

Conclusions:

Preliminary analyses suggest that although overall, individuals with ASD in this study showed decreased speech perception under complex conditions, we also found distinct patterns of neurophysiological differences that may underlie this deficit. Some individuals showed differences in temporal representation (i.e., reduced EFRs) or binaural integration (i.e., poor IPD thresholds) while others did not. Together, these measures provide a robust and promising assay of auditory function with the potential to further our understanding of the mechanisms underlying auditory abnormalities in individuals with ASD by leveraging individual differences.