Low-level Auditory Processing of Simple and Complex Sounds in Autism

Background:  Enhanced and diminished patterns of performance across visual and auditory domains are now a consensual characteristic of the autistic cognitive phenotype (e.g., Mottron et al, 2006). The results of a study by Bertone et al. (2005) suggest that patterns of performance in low-level visual processing tasks may depend on the level of neural complexity required to process stimuli. There are preliminary indications that a dissociation between enhanced and diminished performance linked to the neural complexity required to process acoustic stimuli may exist in the auditory modality as well (Samson et al., 2006). Objectives: The purpose of the current study is to assess the neural complexity hypothesis in the auditory modality.

Methods: To test this hypothesis, four discrimination experiments were designed targeting pitch, spectral envelope, vocal timbre, and loudness. A range of pure- and complex-tone stimuli, with or without frequency or amplitude modulation, varied along spectral and temporal dimensions. An adaptive procedure was used to assess the auditory discrimination thresholds of groups of high-functioning participants with autism (HFA), Asperger syndrome (ASP), and typically developing individuals (TDs). Participants were matched in full scale IQ, chronological age and sex. Our research question was whether increasing the level of spectral and/or temporal complexity would have a detrimental impact on the ability of HFA- and ASP participants to discriminate between acoustic stimuli.

Results: Preliminary results suggest that auditory discrimination performance of the autism spectrum disorders groups is not as dependent on levels of spectro-temporal complexity as originally predicted.

Conclusions: The results will be interpreted in the context of current perceptually based models of enhanced and diminished perceptual functioning in autism.