Auditory Discrimination and Lateralization In ASD

Background:  Numerous studies have shown preserved or enhanced frequency perception in individuals with autism spectrum disorders (ASD; e.g. Bonnel et al., 2003; Heaton, 2003, Järvinen-Pasley & Heaton, 2007). For perception of auditory timing, however, there is evidence of impairment (Alcántara et al., 2003; Groen et al., 2009), and Boucher (2001) proposed that impaired time perception may underlie many of the impairments in autism.  Typically, spectral information (as is used in pitch perception) is preferentially processed in the right hemisphere, and more temporally complex information is preferentially processed in the left hemisphere (Zatorre & Gandour, 2008; Zatorre & Belin, 2001). The evidence of differences in abilities between these two domains implies in individuals with ASD
that there is a lateralization difference in auditory processing in these individuals. 

Objectives:  We used psychophysical methods to investigate discrimination abilities as well as the laterality of processing of spectral vs. temporal information in children aged 10-14 with high-functioning autism or Asperger syndrome and age-matched typical controls. 

Methods:  Participants were 13 with ASD (2 females, 11 males) and 16 with typical development (TD) (7 females, 9 males). They completed a three-alternative forced-choice adaptive psychoacoustic task in two counterbalanced blocks: one tested frequency discrimination at 500, 1000 and 4000 Hz, and the other tested detection of small gaps of silence within a tone (again, 500, 1000 or 4000 Hz) or broadband noise. 

Results:  On the frequency task, the ASD group was impaired relative to the TD group. Results of an ANCOVA showed a main effect of group when IQ, scores on a task of auditory working memory, and sex were added to the model as covariates, F(1, 172) = 13.2, p < 0.01. However, a nonparametric median test of thresholds between groups showed no difference in frequency discrimination, p = .16, suggesting that this effect is small. On the gap detection task, the ASD group again showed impaired performance, F(1, 230) = 21.0, p < .001, along with a laterality difference on the 1000 Hz stimuli in the gap detection task [ear x frequency x group interaction; F(3, 227) = 6.04, p < .001]. In this case, a median test showed a significant difference between group means, p < .001. In addition, in the ASD group there was a subset of 5 poor performers on the gap detection task who performed typically on the frequency discrimination task, and only one who showed the reverse pattern, implying differential processing abilities between these two tasks. 

Conclusions:  Though the ASD group showed some impairment on the frequency task as well as the gap detection task, nonparametric tests showed that their impairment on gap detection was greater than the impairment on frequency discrimination. In addition, the ASD group showed abnormal lateralization on gap detection, but there was no evidence of this abnormality in the frequency task. This study provides further evidence of a specific impairment in time perception, possibly due to atypical lateralization of processing.