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Abstract:
Recent work has demonstrated that the length of
structural dependencies affects sentence complexity and reading
times (e.g., Gibson, 1998; Grodner, Watson & Gibson,
2000). Past investigations of distance have focused on
properties of words intervening between the endpoints of
dependencies, such as the amount of referential processing they
require (Warren, 2001). In this poster, we investigate an
alternative distance metric that past work has not ruled
out.
In his (1998) paper, Gibson calculated the length
of syntactic dependencies according to the distance between the
heads of the dependent clauses. But alternatively, the
length of a syntactic dependency could reflect the distance
between complete constituents rather than their heads. In
this case, distance would be calculated between the right edge of
the first constituent and the left edge of the second
constituent. One location where these distance metrics make
divergent predictions is at the matrix verb of a sentence whose
NP subject is modified by a constituent intervening between its
head and the upcoming verb. If the distance between
complete constituents affects the difficulty of integration then
including a modifier will not affect reading times at the matrix
verb, because the modifier is part of the subject NP
constituent. Alternatively, if the distance between heads
affects the difficulty of integration, then including a modifier
will cause increased reading times on the matrix verb.
Previous studies have manipulated the amount of discourse
processing required in a subject-modifying constituent and shown
that reading times on the matrix verb are longer when more
processing is required during the NP, as predicted by the
head-based distance metric. But in most of these studies,
the embedded verb and matrix verb are in consecutive positions,
so the effects observed at the matrix verb could be spill-over
from the embedded verb.
The two experiments in this poster tested
sentences like (a), where an object-extracted RC modifies the
head of the subject NP. The subject of the RC was either
new to the discourse or had previously appeared in context.
A phrase intervened between the two verbs to eliminate the
possibility of reading time spill-over.
(a) The suspect, who the/a detective had sighted
the previous Wednesday, struggled but was eventually
subdued.
Both experiments showed reliable effects at the
embedded verb, such that conditions requiring more discourse
processing in the subject modifier had longer reading
times. But neither experiment showed any differences in
reading times at the matrix verb. This finding supports a
constituent-based distance metric over a head-based distance
metric.
References
Gibson, E. (1998). Syntactic complexity:
Locality of syntactic dependencies. Cognition, 68(1),
1-76.
Grodner, D., Watson, D., & Gibson, E.
(2000). Locality effects in processing unambiguous
sentences. Talk at 13th Annual CUNY Conference on Human Sentence
Processing, San Diego, CA.
Warren, T. (2001). Understanding the Role of
Referential Processing in Sentence Complexity. Ph.D.
thesis, MIT.
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