Lexical information affects identification of ambiguous phones (Ganong, 1980). Contrary to interactive models of auditory word recognition, recent evidence suggests that this effect is not due to feedback from a lexical to a phonemic processing layer. A phone ambiguous between /s/ and /S/ identified as /s/ following /dZu/ (making "juice" rather than "joosh") does not engender compensation for coarticulatiory effects of /s/ on a following /t/ or /k/ (Pitt & McQueen, 1998). However, compensation for coarticulation by phones identified bottom-up does occur. Because compensation is assumed to be prelexical, these results imply distinct phonological and lexical processing stages linked by a feedforward-only relation.
Lexical information also affects phoneme identification when optical and acoustic information for speech gestures are discrepant (Brancazio, 1998): optical /d/ dubbed onto acoustic /b/ leads to fewer /b/ percepts preceding audiovisual /Ens/ (bense-dense) than preceding /EntS/ (bench-dench). Audio-visual integration also fosters compensation for coarticulation; a visual /l/ dubbed onto an ambiguous acoustic signal increases identification of a following /g/ (Fowler, Brown & Mann, in press). This suggests that audiovisual integration is prelexical.
Our question now is where the lexical effect on audiovisual integration occurs. Does it occur at a lexical stage of processing after audiovisual integration produces bottom-up ambiguity? Or is the effect due to feedback from a lexical level of processing to one at which audiovisual integration and compensation for coarticulation occur?
We are currently running experiments to address this issue. We are testing whether an audiovisually-induced compensation for coarticulation effect will be modulated by a lexical influence on audiovisual integration. A finding that the magnitude of the compensation effect shifts with lexically-induced variation in the visual influence in audiovisual integration would imply that lexical information feeds back onto audiovisual integration. A lexical effect on audiovisual integration that had no effect on compensation for coarticulation would be consistent with a feedforward-only account.
Brancazio, L. (1998). Contributions of the lexicon to audiovisual speech perception. Ph.D. dissertation. University of Connecticut, Storrs, CT.
Fowler, C. A., Brown, J. M., & Mann, V. A. (in press). Contrast effects do not underlie effects of preceding liquid consonants on stop identification in humans. Journal of Experimental Psychology: Human Perception and Performance.
Ganong, W. F. (1980). Phonetic categorization in auditory word perception. Journal of Experimental Psychology, 6, 110-125.
Pitt, M. A., & McQueen, J. M. (1998). Is compensation for coarticulation mediated by the lexicon? Journal of Memory and Language, 39, 347-370.