Autistic Traits and Auditory Perceptual Discrimination

Background: The Enhanced Perceptual Functioning model (Mottron & Burack, 2001; Mottron, et al. 2006) suggests that persons with ASD have enhanced low level processing of basic perceptual information. In the auditory modality enhanced discrimination for pitch is found in children (Bonnel et al. 2003; O’Riordan & Passetti, 2006). Jones et al. (2009) found a subset of an adolescent ASD group to have enhanced ability to discriminate frequency. Memory for basic pitch stimuli is enhanced in ASD (Heaton, 2003). Whether enhanced low level processing occurs in ASD for all basic stimuli, and whether this model holds across the broader autism phenotype has not been tested. Traits or features of ASD are present both in relatives of those with ASD and in the general population (Autism-Spectrum Quotient, AQ Baron-Cohen et al., 2001a; Dawson et al., 2007; Hurley, et al. 2007). These traits are predictive of behaviours similar to those observed in ASD (Bayliss & Tipper, 2005; Baron-Cohen et al., 2001b; Stewart et al., 2009).

Objectives: We assess whether autistic traits predict performance on basic, low level auditory perceptual discrimination tasks of pitch, timing and loudness, by measuring individual thresholds in a reliable, adaptive fashion.
Methods: Participants were recruited from a database who had completed the AQ in order to achieve a range of scores in the sample (Mean AQ Likert scoring total=114.0, range=77 to 150) from Heriot-Watt University (n=24; mean age=22.3, s.d.=3.9; 12 males, 12 females). Ethical approval was obtained from the Ethics Committee of Heriot-Watt University. Participants were asked to discriminate tonal stimuli based on frequency, intensity and timing. The frequency and intensity tasks used a fixed tone reference; the timing task was conducted with a variable and a fixed time interval reference. IQ was assessed by a shortened version of Raven’s Advanced Progressive Matrices (Raven et al., 1998).

Results: AQ scores correlate with thresholds for pitch discrimination (r=-0.51, p<0.05) and the fixed timing task (r=-0.45, p<0.05); as AQ scores increase there is enhanced discrimination of pitch, and timing on the fixed interval task. No correlation was found between AQ and intensity discrimination thresholds or the variable timing task. There was no relationship with AQ and the Raven’s task, nor was there any relationship between the Raven’s task and any of the perceptual tasks.

Conclusions: Autistic traits are predictive of pitch discrimination in a similar way to ASD, suggesting that features normally associated with ASD are also present in the Broader Autism Phenotype. This is the first study to show this relationship, and to show a relationship with timing. This study gives some indication as to the locus of the enhancement, suggesting that a stable representation of the stimuli may be formed. Both timing and pitch are important aspects of understanding aspects of language such as prosody. The literature suggests that basic perceptual processing may be related to language processing (Jones et al., 2009; Heaton et al, 2008), it remains to be tested whether this is the case.