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, 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, 1998; cf. Samuel and Pitt, 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.]