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Abstract:
It is well known that nested structures like (1a)
are much harder to understand than their right-branching
counterparts (1b):
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(1)
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a.
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The student who the professor who
the scientist collaborated with had advised copied the
article.
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b.
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The scientist collaborated with
the professor who had advised the student who copied the
article.
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One factor that has been proposed to account for
the difference in difficulty is integration distance (Gibson,
1998): Integration distances are much longer at the verbs for a
nested structure than for a non-nested structure, making the
nested structure harder. Another factor that has been
proposed to account for the difference is storage: Keeping track
of more incomplete phrase structure rules or predicted categories
could also make nested structures harder (Yngve, 1960; Chomsky
& Miller, 1963; See Gibson, 1998, and Lewis, 1993 for more
recent proposals). This paper used self-paced word-by-word
reading to test whether storage costs exist independent of
integration differences. To investigate this issue, we
compared reading times for sentence regions in which storage
costs varied but integrations remained constant. Experiment
1 manipulated the number of verbs needed to form a grammatical
sentence, using materials like those in (2):
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(2)
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a.
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The employee realized that the
boss implied that the company planned a layoff and so he
sought alternative employment.
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b.
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The employee realized that the
boss's implication that the company planned a layoff was not
just a rumor.
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c.
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The employee's realization that
the boss implied that the company planned a layoff caused a
panic.
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d.
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The employee's realization that
the boss's implication that the company planned a layoff was
not just a rumor caused a panic.
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The target region for all four sentence types is
the most embedded clause "the company planned a layoff". In
(2a), no verbs beyond the target region are needed to make a
grammatical sentence. In (2b) and (2c), one verb beyond the
target region is predicted. In (2d), two verbs beyond the
target region are required. Thus storage cost theories
predict that the target region should be read fastest in (2a),
slower in both (2b) and (2c), and slowest in (2d). The
results of the experiment confirmed these predictions.
Experiment 2 used materials like those in (3) to
investigate whether incomplete dependencies other than those
involving an expected verb also incur storage costs:
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(3)
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a.
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Complement clause
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The claim (alleging) that the
cop who the mobster attacked ignored the informant might
have affected the jury.
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b.
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Relative clause
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The claim which the cop who the
mobster attacked ignored might have affected the
jury.
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The target region consists of the embedded
material "the cop who the mobster attacked". In (3a), the
target material is part of a complement clause (CC) of the noun
"claim". In (3b), the target material is part of a relative
clause (RC) modifying "claim". Of relevance here, the RC
requires the presence of an extra NP dependency position inside
the RC (e.g., the gap NP object of "ignored" in (3b)). If
storing this expectation is associated with processing cost, then
people should read the target region slower for the unambiguous
RC structure in (3b) than for either the ambiguous or unambiguous
versions of the CC structure in (3a). The results of
Experiment 2 verified these predictions (unambiguous CC vs.
unambiguous RC: p's<.05; ambiguous CC vs. unambiguous RC:
p's<.01).
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