The Temporal Resolution Needed for Speech Intelligibility Assessed with Mosaic Speech: Effects of Block Duration, Age, and Word Familiarity

Background/Objectives: Mosaic speech was used to further investigate the auditory system’s temporal resolution needed for speech intelligibility. Mosaic speech is a form of degraded speech segmented in frequency × time blocks with no discernible temporal fine structure and with degraded amplitude envelope cues. Methods: We performed a listening experiment with mosaic speech consisting of 20 frequency bands segmented into 20, 40, 80, 160, and 320 ms. Younger listeners (<25 years; n = 20), with self-reported normal hearing and having passed a limited screening test, and elderly listeners (>65 years; n = 19) with hearing thresholds ranging from normal hearing to moderate hearing loss listened to Japanese low- and high-familiarity mosaic words and wrote down what they heard. The original words were included as control stimuli. Results: Although younger listeners had significantly higher intelligibility scores, elderly listeners could integrate and parse coarse blocks of mosaic speech of 20 ms and 40 ms with intelligibility scores of 84% or higher for high-familiarity words. For longer block durations, however, the elderly listeners’ intelligibility dropped rapidly for both high- and low-familiarity words. In both the young and the elderly listener groups, intelligibility reached the floor for block durations of 160 and 320 ms. Word familiarity strongly affected intelligibility scores. For blocks up to 80 ms, intelligibility was significantly higher for high-familiarity words than for low-familiarity words in both age groups, with a 10–30% difference. Conclusions: Elderly listeners (n = 19) with normal hearing to moderate hearing loss could maintain relatively high intelligibility for mosaic words segmented in blocks of 20 or 40 ms, provided the words had a high familiarity level.