The distinctness of speakers' /s/-/∫/ contrast is related to their auditory discrimination and use of an articulatory saturation effect

This study examines individual differences in producing the sibilant contrast in American English and the relation of those differences to 2 speaker characteristics: (a) use of a quantal biomechanical effect (called a "saturation effect") in producing the sibilants and (b) performance on a test of sibilant discrimination. Twenty participants produced the sibilants /s/ and /∫/ in normal-, clear-, and fast-speaking conditions. The degree to which the participants used a saturation effect in producing /s/ and /∫/ was assessed with a custom-made sensor that measured contact of the underside of the tongue tip with the lower alveolar ridge; such contact normally occurs during the production of /s/ but not /∫/. The acuteness of the participants' discrimination of the sibilant contrast was measured using the ABX paradigm and synthesized sibilants. Differences among speakers in the degree of acoustic contrast between /s/ and /∫/ that they produced proved related to differences among them in their use of contact contrastively and in their discriminative performance. The most distinct sibilant productions were obtained from participants who used contact in producing /s/ but not /∫/ and who had high discrimination scores. The participants who did not use contact differentially when producing the 2 sibilants and who also discriminated the synthetic sibilants less well produced the least distinct sibilant contrasts. Intermediate degrees of sibilant contrast were found with participants who used contact differentially or discriminated well. These findings are compatible with a model of speech motor planning in which goals for phonemic speech movements are in somatosensory and auditory spaces.