Perceptual distinctiveness of dental vs. palatal sibilants in different vowel contexts

This paper reports a similarity rating experiment and a speeded AX discrimination experiment to test the perceptual distinctiveness of dental vs. palatal sibilants in different vowel contexts. The stimuli were pairs of CV sequences where the onsets were [s, ts, tsh ] vs. [ˆ, tˆ, tˆh ] as in Mandarin Chinese and the vowels were [i, a, o]; the durations of the consonants and vowels were set to values close to those in natural speech; the inter-stimulus-interval was set at 100ms to facilitate responses based on psychoacoustic similarity. A significant effect of vowel contexts was observed in the similarity rating by 20 native American English speakers, whereby the dental vs. palatal sibilants were judged to be the least distinct in the [i] context. A similar pattern was observed in the speeded AX discrimination, whereby the [i] context introduced slower “different” responses than other vowels. In general, this study supports the view that the perceptual distinctiveness of a consonant pair may vary with different vowel contexts. Moreover, the experiment results match the typological pattern of dental vs. palatal sibilants across Chinese dialects, where contrasts like /si, tsi, tsh i/ vs. /ˆi, tˆi, tˆh i/ are often enhanced by vowel allophony.