Hearing-in-Noise Perception in ASD

Background:   The ability to filter relevant auditory information from background noise is critical for social communication, and impairment of such filtering abilities is a commonly cited feature of autism spectrum disorder (ASD). Parents and teachers often report that children with ASD have difficulty attending to and understanding speech in noisy environments; these observations are supported by studies using standardized questionnaires of sensory functioning.  While individuals with ASD have difficulties filtering speech in background noise, there may be variability in their abilities related to processing of the auditory target (e.g., speech vs. non-speech), the type of auditory background noise, and the ability of the auditory system to spatially separate the target from the background noise (spatial release from masking).

Objectives: We comprehensively characterized the nature of auditory filtering abilities in children with ASD compared to well matched controls, using both speech and musical tones as targets, speech-shaped noise and synthesized babble as maskers, and spatially matched or separated targets relative to background noise.  

Methods: Children with ASD (n=25) and typically developing controls (n=26), ages 6 through 17, participated in this study. Groups were rigorously characterized via ADI-R and ADOS, and matched on age, gender, and verbal ability. Exclusion criteria included diagnoses of neurological or genetic disorders, and other conditions or illnesses that could affect hearing. Hearing was evaluated via audiometry; all subjects had thresholds <20 dB SPL for 500, 100, 2000, and 4000 Hz, and <25 dB SPL for 8000 Hz.

Testing was conducted in a sound attenuated room, and included i) speech-in-noise intelligibility using the Hearing-in-Noise Test (HINT); and ii) forced-choice tonal perception-in-noise using the same protocol used for the HINT, but replacing speech with 3-4 tone differences.  Control conditions included response to similar targets in quiet (which yielded no group differences).

Results:   Children with ASD exhibited significantly impaired hearing-in-noise abilities compared to controls for speech targets (p=.003). This group difference persisted when the masking noise consisted of babble (p=.01). Importantly, children with ASD also demonstrated worse abilities relative to controls when targets were musical tones (p=.03), suggesting that hearing in noise is not specific to language. Across all three conditions, the average signal-to-noise ratio for the autism group was roughly 2 dB higher than their matched peers.  Children with ASD also showed no differences in spatial release from masking; both groups demonstrated the same pattern of better performance when the signal and noise were spatially separated.

Conclusions:   These results confirmed significant impairment in hearing-in-noise across both speech and non-speech targets. Based on our findings, a newly developed forced-choice tone-in-noise test may be used to assess auditory filtering abilities in younger populations with ASD or those who have limited verbal abilities (who would therefore not be able to be tested using traditional speech-in-noise measures).  This extension would then allow for further investigation of the specificity of auditory filtering impairment and its role in social-communicative functioning and language development across a broader age and ability span.