Given that syntactic analysis seems
to be part of language comprehension, the question of exactly how
the reader or listener determines the syntactic structure of a
sentence (sentence parsing) becomes a central concern.
Researchers have examined this question by presenting sentences that
contain a syntactic ambiguity, that is, a situation in which more
than one well-formed synatctic analysis can be assigned to a string
of words. Usually, subsequent words indicate the correct
analysis. For example:
(1) The lawyer
charged that the defendant was lying.
the defendant was lying.
In (1), there is little syntactic
ambiguity. By contrast, in (2) the grammatical role of the noun
phrase the defendant is temporarily ambiguous between an
"object of the verb" role and a "subject of an upcoming clause"
role. The fact that the subject role is appropriate in this
case becomes clear only after encountering the disambiguating
was. Current theories predict that in such
situations the reader will assign the object role to the
defendant. This decision will result in a processing
problem when the auxiliary verb is encountered; under the object
analysis, the auxiliary cannot be attached to the preceding sentence
material. Consequently, this theory predicts that readers
should (at least momentarily) perceive the auxiliary verb to be
syntactically anomalous. The prediction, then, is that the
auxiliary verb in (2) should elicit a P600 effect, relative to the
same word in (1). The figure plots ERPs to the final three
words in each sentence (defendant was lying). Arrows
indicate the onset of each word. Consistent with the
prediction, beginning at about 500 ms after onset, auxiliiary verbs
in sentences like (2) elicited a P600-like positive shift.
One interpretation of these results is that readers commit
themselves to a single syntactic analysis when confronted with
ambiguity, rather than building all possible structures in parallel
or waiting until disambiguating information indicates which analysis
is the correct one before assigning grammatical roels to words.
Just as importantly, these results show that the P600 effect is
elicited not only by outright ungrammaticalities, but also by
perceived ungrammaticalities that result solely due to how people
Osterhout, L. (1997). On the brain
response to syntactic anomalies: Manipulations of word position and
word class reveal individual differences.
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