The [s -- > ʃ] sound change in /str-/ contexts: how temporal changes in the acoustic spectrum affect fricative percept

Abstract

Studies have documented a sound change in some English dialects whereby /s/ in the context /strV/ surfaces as [ʃtrV]. This can be interpreted as /s/ rounding for the rhotic being re-analyzed as [ʃ]. We recently measured F;M, the frequency of the main peak in mid-fricative spectra, in seven adults producing words with /s/ and /ʃ/ across phonetic contexts and compared the acoustics to perceptual rankings on an [ʃ] to [s] scale. One speaker exhibited a perceived sound change; two, partial sound changes. It was shown that F;M was correlated with the perceptual rankings for /strV/ words. However, in all speakers, lowered F;M for /s/ in labial contexts did not affect percepts. The time course of lip rounding and tongue-tip retraction in /strV/ could help differentiate coarticulation versus a phonemic change. Interestingly, however, X-Ray Microbeam data [Iskarous, K. et al. (2011) Articulatory-acoustic kinematics of /s/, J. Acoust. Soc. Am. 129, 944-954] showed that / s/ constriction location was constant over time except in /str-/ context. This study will assess the amount and timing of F;M lowering, its perceptual consequences and likely articulatory causes, to gain more insight into the [strV] -- > [ʃtrV] sound change.