Earlier research suggests that the lexical access process in humans is highly intolerant of mismatch. When heard in isolation, a sequence such as [wikib] (wickib) is unacceptable as a token of wicked even though the mismatch is minimal. This observation is apparently inconsistent with the vulnerability of natural speech to phonological change. For example, the word wicked m a y be phonetically realised as [wikib] in the context of "wicked prank". This is an example of place assimilation, where the underlying /d/ in wicked acquires a labial character from the foUowing labial consonant. The cross-modal priming experiments reported here test the hypothesis that phonologically regular variation does not in fact create mismatch when it occurs in the appropriate context. Subjects heard tokens like [wikib] embedded in either phonologically viable context (where the following word was prank) or in unviable context (where the following word was game ) . When heard in unviable context, the distorted tokens produced a strong mismatch effect In contrast, the distorted tokens in viable context primed as strongly as the undistorted words. These results suggest that the on-line processes of speech interpretation and lexical access must perform some kind of phonological inferencing when interpreting speech at the lexical level.

Cross-modal priming experiments have shown that surface variations in speech are perceptually tolerated as long as they occur in phonologically viable contexts. For example, [klim] {cleam) gains access to the mental representation of clean when in the context of [klimpoks] (cleam parks), since the change is a natural one, reflecting the phonological process of place assimilation. This implies that speech perception involves processes of phonological inference, which recover the underlying form of speech. Here we investigate the locus of these inference processes, using the phoneme monitoring task. A set of stimulus sentences were created containing deviations that were either phonologically viable (as in cleain parks above) or unviable. In Experiment 1, subjects monitored for the segment underlying the surface change (in the above example, /n/) and in Experiment 2 the following segment (/p/) was the taiget. In addition, the lexical status of the carrier word was manipulated (e.g., clean vs threan), contrasting lexical and non-lexical theories of phonological inference. Both experiments showed stiong effects of phonological viability for real words, with weaker effects for the non-word stimuli. These results suggest that phonological inference can occur non-lexically, but that it interacts strongly with the process of lexical access.