Tone processing and the acquisition of tone in Mandarin- and English-speaking typically developing children and children with Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is characterised by pervasive social difficulties, which partly manifest themselves in inappropriate pragmatics. It has also been hypothesised that individuals with ASD, or at least those on the lower-functioning end of the autism spectrum, may also have atypical pitch and musical perception. This thesis investigates pitch perception in autism in a domain where pitch is directly represented in the grammar: tones. Tone perception was investigated in a series of four experiments with high-functioning English and Mandarin ASD participants with and without language problems and their corresponding TD groups. The first experiment involved a tone comprehension task (only for the Mandarin participants) using picture-matching. The second experiment involved a psychoacoustic tone discrimination task using the Mandarin Tone 1-4 continuum. The third experiment was a categorical perception task involving two tasks: a naming task and a two-step identification task. The results of the experiments indicated subtle but persistent issues with the grammatical representation of tones for Mandarin ASD speakers, especially for those with language problems. Although ASD participants’ tone comprehension and tone discrimination abilities are essentially in line with their typical peers, they have different error patterns in comprehension of Tone 2-3 distinctions and they treat nonce word stimuli more like pure tone stimuli in identification, suggesting a weaker representation of abstract tones. In addition, the categorical perception task revealed that although the performance of Mandarin ASD participants in the naming task was not distinguishable from their typically developing peers, the two-step identification task revealed a less strongly categorical perception of the Tone 1-4 continuum. In addition, the performance of the ASD SLP groups was also overall worse. These results altogether constitute a significant discovery of a grammatical impairment of people living with ASD. This population might have prosodic impairments relating their pitch perception, and their ability to categorise pitch contours in a grammatical fashion, in addition to their pragmatic difficulties.