Intact Auditory Processing but Impaired Speech Perception in Adolescents with Autism Spectrum Disorder and Early Language Delay

Background:  Language impairment and atypical sensory processing are often reported in autism spectrum disorders (ASD). In individuals with ASD, particularly in those with weak verbal abilities, an intriguing discrepancy has been observed between superior pitch processing and inferior auditory temporal and speech processing abilities. Studies in typically developing individuals (TD) have linked left hemispheric specialization for speech and language to an asymmetry in cortically auditory tuning: left auditory cortex is particularly sensitive to temporal aspects and faster modulations, whereas spectral aspects, like pitch, are preferentially processed in right auditory cortex. Against this background, it has been hypothesized that the pattern of superior pitch processing and impaired auditory temporal, speech and language processing in ASD may reflect superior right hemisphere versus inferior left hemisphere processing. Alternatively, it has been suggested that this pattern of assets and deficits could also be interpreted as evidence for the more domain-general Weak Central Coherence (WCC) or Enhanced Perceptual Functioning (EPF) theories of ASD.

Objectives:  We assessed a broad range of low-level auditory and speech processing abilities, as well as general language skill, to investigate whether the observed pattern of assets and deficits favors the evidence for the Atypical Hemispheric Specialization hypothesis or rather for the WCC or EPF theories.

Methods:  A series of psychophysical measures and language tasks were administered in 20 adolescents with ASD and early developmental language delay and 20 matched TD controls. Auditory measures were selected to preferentially target right auditory cortex (frequency discrimination, 4 Hz AM) and left auditory cortex processing (gap-in-noise detection, 20 Hz AM). Speech perception measures comprised the perception of words and sentences in various types of noise (i.e. stationary, fluctuating and babbling noise) to investigate the impact of increasing contextual information and spectrotemporal complexity of the background noise, respectively. Language measures comprised various phonological tasks and general expressive and receptive language tasks.

Results:  Preliminary analyses confirmed that the ASD group shows severe and broad language impairments, as well as deficits in speech perception, in particular for sentence perception in spectrotemporally complex background noise. There were no group differences on any of the low-level auditory measures.

Conclusions:  The pattern of superior spectral and inferior temporal auditory processing could not be replicated in this sample of adolescents with ASD and early language impairment. Given the similar performance in both groups, the obtained auditory profile could not be related to any advantageous or preferential hemispheric processing. Yet, the severe deficits in basic speech-in-noise perception are intriguing and point to an inability to efficiently integrate socially relevant auditory information.