Ambiguity in sentence processing.

As listeners and readers, we rarely notice the ambiguities that pervade our everyday language. When we hear the proverb `Time flies like an arrow' we might ponder its meaning, but not the fact that there are almost 100 grammatically permissible interpretations of this short sentence. On occasion, however, we do notice sentential ambiguity: headlines, such as `Two Sisters Reunited After 18 Years in Checkout Counter', are amusing because they so consistently lead to the unintended interpretation (presumably, the sisters did not spend 18 years at the checkout). It is this consistent preference for one interpretation-and one grammatical structure-rather than another that has fuelled research into sentence processing for more than 20 years. Until relatively recently, the dominant belief had been that these preferences arise from general principles that underlie our use of grammar, with certain grammatical constructions being preferred over others. There has now accrued, however, a considerable body of evidence demonstrating that these preferences are not absolute, but can change in particular circumstances. With this evidence have come new theories of sentence processing, some of which, at first glance, radically question the standard notions of linguistic representation, grammar and understanding.