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Disfluency Effects in Comprehension 2 Natural speech production often includes disfluencies, such as mid-utterance hesitations, filler words (“um”, “uh”), repeated or repaired words, and pronouncing “the” as /thiy / (rhyming with “tree”) or “a ” as /ey / (rhyming with “say”) (Fox Tree & Clark, 1997). Yet laboratory research typically ignores disfluency. We describe an on-going research program that demonstrates how disfluency information affects on-line reference comprehension. In two eyetracking experiments, listeners followed instructions like “Put the grapes below the candle. Now put {the / thiy uh} candle… ” Their eye movements at the word “candle ” in the second instruction revealed a preference for given objects when the instruction was fluent, and for new objects when the instruction was disfluent. An offline experiment supported the idea that the fluency or disfluency in the article affect listeners expectations about what the speaker is referring to. These results are discussed in terms of how disfluency affects the accessibility of referents during reference comprehension