Sequential contrast or compensation for coarticulation?

Abstract

English listeners identify a stop ambiguous between /t/ and /k/ more often as ‘‘k’’ after [s] than [sh] (Mann and Repp, J. Acous. Soc. Am. 69, 548–558, 1981). Judgments shift similarly after a fricative ambiguous between [s] and [sh] when its identity is predictable from a transitional probability bias but perhaps not from a lexical bias (Pitt and McQueen, J. Mem. Lang. 39, 347–370, 1998, cf. Samuel and Pitt, J. Mem. Lang. 48, 416–434, 2003). In replicating these experiments, we add a discrimination task to distinguish between the predictions of competing explanations for these findings: listeners respond ‘‘k’’ more often after [s] because they compensate for the fronting of the stop expected from coarticulation with [s] or because a stop with an F3 onset frequency midway between [t]’s high value and [k]’s low value sounds lower after the [s]’s high-frequency energy concentration. The second explanation predicts listeners will discriminate [s-k] and [sh-t] sequences better than [s-t] and [sh-k] sequences because sequential contrast exaggerates the spectral differences between [s-k]’s high-low intervals and [sh-t]’s low-high intervals and distinguishes them more perceptually than [s-t]’s high-high intervals and [sh-k]’s low-low intervals. Compensation for coarticulation predicts no difference in discriminability between the two pairs because it does not exaggerate differences between the two intervals. [Work supported by NIH.]