Roger Levy

Roger Levy of the UCSD Linguistics Department will speak at the UCSD Linguistics Department Colloquium on October 12, 2009, at 2:00 pm in AP&M 4301.

The Processing of Extraposed Structures in English

In most languages, most of the word-word dependency relations found in any given sentence are projective: they do not cross other word-word dependencies in the sentence. Some dependencies, however, are non- projective, crossing other dependencies in the sentence. Crossing dependencies are both rarer and more computationally complex than projective dependencies; hence, it is of natural interest to investigate whether there are any processing costs specific to crossing dependencies, and whether factors known to influence processing of conventional dependencies also affect crossing- dependency processing. We report four self-paced reading studies, together with corpus studies, investigating the comprehension difficulty associated with the crossing dependencies created by the extraposition of relative clauses in English. We find that extraposition over either verbs or prepositional phrases creates comprehension difficulty, and that this difficulty is consistent with probabilistic syntactic expectations estimated from corpora. Furthermore, we find that manipulating the expectation that a given noun will have a postmodifying relative clause can modulate and even reverse the difficulty associated with extraposition. Our experiments rule out accounts based purely on derivational complexity and/or dependency locality in terms of linear positioning. This is the first demonstration that comprehenders maintain probabilistic syntactic expectations that persist beyond projective-dependency structures, and suggests that it may be possible to explain observed patterns of comprehension difficulty associated with extraposition entirely through probabilistic expectations.