Enhanced Perception of Pitch Direction In Young Adults with Autism Spectrum Disorder

Background:  

Enhanced pitch perception has been previously documented in autism spectrum disorders (ASD), particularly in the context of discrimination and categorization tasks (e.g., Bonnel et al., 2010).  However, to our knowledge, no one has yet specifically examined higher-order perception such as pitch change direction in ASD, and if individuals with ASD maintain superior pitch processing even under challenging experimental conditions.

Objectives:  

The objectives of the present research were to: 1) test whether perception of pitch direction is enhanced in ASD individuals relative to typically-developing controls; 2) to test if ASD individuals maintain enhanced pitch perception under conditions in which they are often found to be impaired, such as at fast temporal rates of presentation (e.g., Gepner and Feron, 2009), 3) to investigate whether ASD individuals with and without delayed speech onset show different performance profiles on a pitch direction task.

Methods:

We tested three subject groups: 1) 10 autism spectrum individuals (ASD) with delayed speech onset (DSO) (defined as first words after 24 months and/or first phrase after 33 months old), 12 ASD with typical speech onset (TSO), and 12 typically developing individuals (TYP).  All groups were matched on IQ, age (mean 21), gender and manual preference.

In a pitch change direction task (Gougoux et al, 2004), subjects heard two pure tones of different frequencies on each trial and had to decide whether the pitch rose or fell. Task difficulty was parametrically manipulated from a reference condition, in both the temporal and spectral domains, either by successively dividing tone duration by two (temporal series), or by dividing the frequency spacing between the tones by two (spectral series). Subjects heard stimuli through headphones binaurally and reported the pitch-change direction by pressing a key.

Ethical approval for the present work was obtained in accordance with the National Institute of Health guidelines.

Results:

For all groups, performance was best in the reference condition and was significantly reduced when either the tone duration, or the frequency difference between the tones was decreased.  The ASD-DSO and TSO groups combined showed significantly better performance relative to CTR overall, even at the fast temporal rates.  Each of the ASD-DSO and ASD-TSO groups alone performed better than CTR overall.  However, the ASD-DSO showed more significant enhanced performance and at all of the spectral and temporal difference levels.

Conclusions:  

We extend previous findings in ASD by demonstrating novel results of enhanced pitch change direction judgement in ASD. Thus, the pitch processing superiority in ASD extends to higher levels than just simple pitch discrimination tasks.  These findings contribute to a better understanding of the cognitive architecture of perceptual processing in ASD with respect to the theory of Enhanced Perceptual Functioning (Samson et al., 2006).  Importantly, enhanced pitch direction perception was found in ASD even when the pitch changes were presented at fast temporal rates.  These findings are provocative since they are in contrast to the view that ASD individuals are generally impaired in processing information at fast temporal rates of transition.