Perceptual effects of lexical competition on Cantonese tone categories

Abstract

Listeners use lexical information and the speech signal to categorize sounds and recognize words despite substantial acoustic-phonetic variation in natural speech. In diachronic mergers, where systematic variation acts to neutralize lexical contrasts, the role of the lexicon becomes less clear. We examined how lexical competition structures phonetic variability of (merging) lexical tone categories in Cantonese using three experiments. Listeners categorized tokens from lexical tone continua generated from minimal pairs (Experiment 1: Word identification) and categorized tokens from tone continua generated from word-nonword pairs (Experiment 2: Lexical decision). The presence of a lexical competitor at both continuum endpoints in Experiment 1 maintained more discrete categorization functions for non-merging tone pairs than in Experiment 2 where only one endpoint was a word. In the merging tone pairs, categorization was less discrete and the effect of lexical competition was different. Exploratory data from a goodness rating task, Experiment 3, suggest that lexical competition affects internal category structure for merging tones, but not non-merging tones. Overall, these data provide evidence that tone mergers affect phonetic category boundaries and internal category structure in the lexicon, and that, for non-merging tones, the range of acceptable phonetic variation is constrained by the presence of a lexical competitor.