Perceptual and articulatory factors underlying the typology of sibilant place contrast

In a sound sequence, the coarticulation between adjacent segments may lead to context-specific quality of a segment, such that the acoustic and perceptual properties of a consonant may vary in different contexts (Liberman et al. 1952, Kewley-Port 1982, Sereno et al. 1987, Mann & Soli 1991, among others). For two consonants in a phonological contrast, therefore, it is sometimes the case that the contrast is present in one context but not in another (Steriade 1999, 2008). For sibilant place contrasts, typological studies on geographically distant languages revealed a tendency to avoid a three-way place contrast in the [_i] context (Lee-Kim 2014), e.g., *[si-ɕi-ʂi], while allowing the contrast in other vowel contexts, consistent with the results of perceptual experiments that the [_i] context may introduce a reduced accuracy in identifying the place of a sibilant (Lee-Kim 2014) or discriminating two sibilants at different places (Li & Zhang 2017). For this typological pattern, what remains unclear is if the tendency to avoid sibilant place contrast in the [_i] context is modulated by sibilant inventory, i.e., if it applies to languages with sibilants at two places vs. three places alike. A natural hypothesis could be that the tendency is more likely to apply to languages with a three-way place distinction (e.g., [s-ɕ-ʂ]) than those with a two-way place distinction (e.g., [s-ɕ]) as the space of sibilant inventory in the former is expected to be more crowded than that in the latter.
This study examines the phonotactics of sibilants and the vowel [_i] across 159 Chinese dialects, including (i) 62 dialects with sibilants at three places (e.g., [s-ɕ-ʂ]) and (ii) 97 dialeccts with sibilants at two places (e.g., [s-ɕ]). It turns out that, in both groups, there is a clear tendency to avoid sibilant place contrasts in the [_i] context. While the pattern in group (i) confirms the tendency observed in the literature (Lee-Kim 2014), the pattern in group (ii) suggests that it is not necessarily modulated by the size of sibilant inventory. This study argues that perceptual and articulatory factors both underlie the typology. First, the avoidance of sibilant place contrasts in the [_i] context might be more relevant to the phonetic similarity between sibilants at two particular places than to the overall crowdedness of a sibilant inventory. A speeded AX discrimination experiment was conducted to examine the potential interaction of sibilant place difference and vowel context in the perceptual distinctiveness of sibilant place contrasts. The results suggest that [si-ɕi] is perceptually less distinct than [sa-ɕa] but [si-ʂi] is as distinct as [sa-ʂa], indicating that the [_i] context may not necessarily lead to a reduced perceptual distinction for sibilants across different places. Second, for the dialects with a three-way place distinction of sibilants, the general avoidance of a retroflex sibilant plus a vowel [i] (e.g., *[ʂi]) is likely to be rooted in the incompatibility of the articulatory gestures in a retroflex sibilant vs. those in a high front vowel [i] (Pulleyblank 1984, Hamann 2003). The results from ultrasound investigation confirms that, while not necessarily having a curling back of tongue tip, a retroflex [ʂ] usually involves a low tongue blade, which would conflict with a high front vowel and would require more articulatory effort in producing a [ʂi] sequence than a [si] or [ɕi] sequence. In general, the analyses support the contention that perceptual and articulatory factors may take effect in shaping the typology of speech sounds.
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