Categorical perception of speech sounds in adults who stutter.

Stuttering is often attributed to the impaired speech production system, however, there is growing evidence implicating issues in speech perception. Our previous research showed that children who stutter have similar patterns but slower categorical perception (i.e. the ability to categorise different acoustic variations of the speech sounds into the same or different phonemic categories) compared to the children who do not stutter. This study aimed to extend our previous research to adults who stutter (AWS) using the same categorical perception paradigm. Fifteen AWS and 15 adults who do not stutter (A WNS) were recruited to complete identification and discrimination tasks involving acoustic variations of Cantonese speech sounds in four stimulus contexts: consonants (varying in voice onset times, VOTs), lexical tones, vowels and pure tones. The results showed similar categorical perception between the two groups in terms of the boundary position and width in the identification task and between-category benefits in the discrimination task. However, there were some trends for lower discrimination accuracy (overall d' scores) and slower discrimination of the between-category stimuli versus within-category stimuli for AWS than AWNS. These results partially confirm our previous finding on children in terms of a comparable pattern of categorical perception between the two groups, but slower processing speed to access the phoneme representations in speech perception among AWS than AWNS.