Checkerboard and interrupted speech: Critical intelligibility differences observed in factor-analysis-based checkerboard speech stimuli

Abstract

It has been shown that the intelligibility of checkerboard speech stimuli, in which speech signals were periodically interrupted in time and frequency, drastically varied according to the combination of the number of frequency bands (2–20) and segment duration (20–320 ms). However, the effects of the number of frequency bands between 4 and 20 and the ways of frequency divisions on intelligibility have been basically unknown. Here we show that 8-band checkerboard speech stimuli were more intelligible than temporally interrupted speech stimuli and 4-band checkerboard speech stimuli, irrespective of segment duration (n = 19 and 20). At the same time, U-shaped intelligibility curves were observed for 4-band and possibly 8-band checkerboard speech stimuli. Furthermore, when the frequency divisions were determined according to regular intervals on a critical bandwidth scale rather than factor analysis results of speech power fluctuations, intelligibility improved at the 160- and 320-ms segment duration. These results suggest that the factor-analysis-based frequency bands perform as speech cue channels that are essential for speech perception and that a probability summation model based on a perceptual unit of speech perception may account for the U-shaped intelligibility curves if the model is modified to include the speech cue channels.