To understand spoken language, listeners combine acoustic-phonetic input with expectations derived from context (Dahan & Magnuson 2006). Eye-tracking studies on semantic context have demonstrated that the activation levels of competing lexical candidates depend on the relative strengths of the bottom-up input and top-down expectations (cf. Dahan & Tanenhaus, 2004). In the grammatical realm, however, graded effects of context on lexical competition have been predicted (Magnuson, Tanenhaus. & Aslin, 2008), but not demonstrated. In the current eve-tracking study, participants were presented with target words in grammatically unconstraining (e.g., "The word is...") or constraining (e.g., "They thought about the...") contexts. In the grammatically constrained, identity-spliced trials, in which phonetic information from one token of the target was spliced into another token of the target, fixations to the competitor did not differ from those to distractors. However, in the grammatically constrained, cross-spliced trials, in which phonetic information from the competitor was cross-spliced into the target to increase bottom-up support for that competitor participants fixated more on contextually inappropriate competitors than phonologicallv unrelated distractors, demonstrating that sufficiently stiong acoustic-phonetic input can overcome contextual constraints. Thus, although grammatical context constrains lexical activation, listeners remain sensitive to the bottom-up input. Taken together, these results suggest that lexical activation is dependent upon the interplay of acoustic-phonetic input and top-down expectations derived from grammatical context.
