The boundaries of auditory perception for within-word syllable segregation in untrained and trained adult listeners

Syllable segregation is among the core diagnostic features of both childhood apraxia of speech and acquired apraxia of speech; however, little is known about the limen of perception of syllable segregation. The purpose of this research was therefore to explore adult listeners' auditory perception of within-word syllable segregation in trained and untrained adult listeners. Two experimental design studies, each with two phases, were conducted. Study one included 40 untrained listeners (aged 18-28 years), and study two included 5 trained listeners (10-25 years of experience). Recorded audio samples of multisyllabic non-words were manipulated to insert gaps of increasing length to simulate syllable segregation. All stimuli were anchored against an unaltered control sample. In each phase, 32 stimuli were randomly presented twice in a free-field listening task with listeners making Yes/No decisions to record their perception of segregation. At a 90% accuracy threshold, the untrained listeners' limen was 90ms, while the trained listeners' was 85ms. At an 80% accuracy threshold, both sets of listeners had a limen of 80ms. Overall, there were no significant differences in accuracy between the two listening groups. Gap duration was positively correlated with accurate perception across both studies. Both groups demonstrated good intra-rater reliability and excellent inter-rater reliability, with no significant differences between the untrained and trained listeners. These findings have implications for developing a standardised criteria for rating syllable segregation in clinical contexts. No evidence was found for the hypothesis that training makes a difference in listeners' accuracy or reliability when rating syllable segregation.