Pitch Perception in Autism Is Associated with Superior Non-Verbal Abilities

Background: Many individuals with Autism Spectrum Disorders (ASD) have atypical auditory perception and concurrent language impairments. Studies have reported enhanced abilities in ASD for both low-level pitch discrimination  (Bonnel, 2010) as well as higher-level global-local pitch processing (Heaton, 2005), resulting in heterogeneous auditory profiles.  Despite this, auditory perception in ASD remains poorly understood and it is unclear how performance on these different auditory tasks interacts with development of verbal and non-verbal cognitive abilities in ASD.

Objectives: The objectives of the present research were to examine the effect of verbal and non-verbal cognitive abilities on both low-level (pitch direction) and higher-level pitch processing (global-local pitch perception) tasks in children with ASD and typically developing (TD) controls.

Methods: Participants were 17 children with high-functioning ASD and 19 TD children who had no neurological or psychiatric history, and were recruited from the NeuroDevNet ASD Project (Zwaigenbaum et al, 2011). Groups were matched on age (mean age 13.3 years, range 9-18 years) and IQ (mean IQ 113.5, SD 13.6). Verbal and non-verbal cognitive abilities were measured using verbal IQ and performance IQ of the Wechsler's Abbreviated Scale of Intelligence (WASI). Additionally, in the ASD group ADI-R, ADOS and CELF-4 were used to assess language abilities. In the low-level pitch task (Foster et al., 2014), participants heard two tones of different frequencies on each trial and judged whether the pitch rose or fell. In the higher-level global-local task (Ouimet et al., 2012), stimuli consisted of 9-tone melodies, each comprising three triplet (3-tone) sequences. Participants discriminated between ascending and descending pitch direction at the global (across triplets) or local (within triplets) level.  In all tasks, the relationship between task performance (percent accuracy) and verbal/ non-verbal abilities was assessed using linear regression.

Results: Performance oneach of the pitch tasks was not related to verbal ability in ASD or TD (all P>0.05).  However, performance across participants on both low- and high-level pitch tasks was significantly related to non-verbal ability (both P<0.05), primarily the ‘Blocks’ subtest of the WASI (both P<0.05).  For the high-level global pitch task alone, there was a significant interaction between group and non-verbal (performance) IQ (P=0.05), predominantly for the ‘Blocks’ subtest (P=0.05).  This interaction was driven by the fact that TD showed a positive relationship between performance on global pitch judgments and the ‘Blocks’ subtest, whereas ASD showed a negative relationship between these measures (Figure 1).

Conclusions: The present findings suggest that verbal abilities do not predict performance on low or higher-level pitch tasks in TD or ASD.  However, non-verbal abilities (especially the ‘Blocks’ subtest) predict better auditory perception in general, and particularly on higher-level global-pitch tasks in TD. These findings suggest that previously reported superior auditory perceptual skills in ASD might be observed only in a subset of individuals with verbal impairments. However, in IQ-matched, high-functioning ASD individuals without a language delay, pitch discrimination abilities are comparable in ASD and controls, and more related to non-verbal rather than verbal skills.