Korean listeners' identification and discrimination of lengthened /s/ as prolongations

This study aimed to examine Korean listeners' judgement of sound duration as prolongation and the mode of perceiving prolongation, whether discrete or continuous. A total of 75 Korean undergraduate students listened to the Korean segment /s/, each of which was lengthened by 0-380 ms (ranging from the original 205 to 585 ms) in 20-ms increments. Then, the participants were asked to complete two different primary tasks: determine whether the sound was normal (0) or abnormal (1) and rate each version of the sound based on a rating of 1 to 100 (the closer to 100, the less fluent). The minimum duration for the Korean sound to be perceived as abnormally prolonged was calculated by analysing the receiver operating characteristic (ROC) curves using Youden's index. To examine whether listeners perceived durational variations for the fricative segment discretely or continuously, a curve was estimated using the best fitting regression model for the observed data with the highest adjusted R-squared value. The minimum duration identified as abnormal prolongation for the Korean lenis fricative /s/ was 375 ms, corresponding to 182.9% of the original, unaltered sound's length. The mode of perceiving durational variations for the segment was continuous (or gradient) rather than discrete. No gender difference was found in the minimum durational threshold and the mode of perceiving prolongation. The findings of this study were further discussed in relation to the existing body of research, and some clinical implications for the assessment of stuttering were also presented.