Objectives: To investigate the regional functional specialization of the neural responses to sounds varying in spectral and temporal complexity and to test if atypical allocation of neural resources in autism extends to audition.
Methods: Using a 3T MRI system and echo-planar imaging, we studied autistics and controls, matched on FSIQ, sex and age, while they listened to auditory stimuli that varied parametrically in spectral ( two harmonic modulation levels) or temporal (four frequency modulation levels) complexity. Participants were asked to detect the presence or absence of the modulations. We used ANOVA to identify group, task and group by task interaction effects.
Results: We observed between-group differences in sensitivity to temporal complexity in bilateral non-primary auditory areas, with a stronger linear effect of increasing frequency modulation in controls. In contrast, we did not observe between-group differential sensitivity to spectral complexity, as assessed by harmonic stimulus content.
Conclusions: Consistent with predictions of the complexity hypothesis, increasing temporal complexity results in stronger modulation of non-primary auditory areas in controls than in autistics. In contrast, harmonic modulation does not. These results suggest that the complexity hypothesis holds for temporal, but not spectral, domains of auditory perception in autistics.