Recalibration of phonetic categories by lipread speech versus lexical information.

Listeners hearing an ambiguous phoneme flexibly adjust their phonetic categories in accordance with information telling what the phoneme should be (i.e., recalibration). Here the authors compared recalibration induced by lipread versus lexical information. Listeners were exposed to an ambiguous phoneme halfway between /t/ and /p/ dubbed onto a face articulating /t/ or /p/ or embedded in a Dutch word ending in /t/ (e.g., groot [big]) or /p/ (knoop [button]). In a posttest, participants then categorized auditory tokens as /t/ or /p/. Lipread and lexical aftereffects were comparable in size (Experiment 1), dissipated about equally fast (Experiment 2), were enhanced by exposure to a contrast phoneme (Experiment 3), and were not affected by a 3-min silence interval (Experiment 4). Exposing participants to 1 instead of both phoneme categories did not make the phenomenon more robust (Experiment 5). Despite the difference in nature (bottom-up vs. top-down information), lipread and lexical information thus appear to serve a similar role in phonetic adjustments.