The impact of first and second formant variations on vowel identification among elderly Japanese listeners

Correct vowel identification is important for effective speech communication. While vowel perception largely requires accurate processing and detection of spectral information, spectral processing abilities (suprathreshold deficits such as difference limens for frequency) have been shown to degrade with age, and therefore potentially affecting elderly listeners’ vowel categorisation. The current study examined a group of near-normal hearing elderly listeners matched in age, hearing thresholds, auditory filter bandwidths and cognitive performance on their difference limens for frequency (DLFs) and vowel identification. Japanese has a five-vowel system, where/o/ and/e/ approximately differ in second formant (F2) frequencies and/a/ and/u/ approximately differ in first formant (F1) frequencies. We created two continua differing in F1 and F2, respectively, and examined elderly listeners’ identification of the vowels. We found differences in DLFs within the elderly listeners’ group, where the group with lower difference limens (LDL) to have similar DLFs to a control group of young listeners. Grouping the listeners according to their DLFs via k-means clustering with the young listeners’ results, we found the two groups to differ in their/o/ -/e/ (F2) vowel perception, where we observed a significant shift in the boundary between the two groups, but not when F1 was manipulated. This suggests that for elderly listeners, vowel identification that depends on higher formant cues may be affected by frequency discrimination abilities. However, the results did not suggest a difference in accuracy, but instead, a difference in how categories are assigned. • Japanese elderly listeners’ vowel perception varying in F1 and F2 was examined. • Listeners were grouped according to their frequency discrimination abilities (DLF). • A shift in perceptual boundary observed between the groups when F2 is manipulated. • No difference when F1 is manipulated.