Gradient sensitivity to within-category variation in words and syllables.

Five experiments monitored eye movements in phoneme and lexical identification tasks to examine the effect of within-category subphonetic variation on the perception of stop consonants. Experiment 1 demonstrated gradient effects along voice-onset time (VOT) continua made from natural speech, replicating results with synthetic speech (B. McMurray, M. K. Tanenhaus, & R. N. Aslin, 2002). Experiments 2-5 used synthetic VOT continua to examine effects of response alternatives (2 vs. 4), task (lexical vs. phoneme decision), and type of token (word vs. consonant-vowel). A gradient effect of VOT in at least one half of the continuum was observed in all conditions. These results suggest that during online spoken word recognition, lexical competitors are activated in proportion to their continuous distance from a category boundary. This gradient processing may allow listeners to anticipate upcoming acoustic-phonetic information in the speech signal and dynamically compensate for acoustic variability.