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Abstract:
Nouns and verbs convey different aspects of the world and
play different roles in language (e.g., Gentner, 1981). This raises
the question of whether these different word classes are
represented differentially in the brain and/or used differentially
during on-line processing. Recent neuropsychological and imaging
data have suggested differences in where and how these items are
stored in the brain, with nouns argued to be more heavily connected
with posterior systems involved in visual object processing and
verbs more heavily connected to frontal, action- and
motor-processing regions (e.g., Damasio and Tranel, 1993). Such
differences in lexical representation would clearly have
implications for sentence processing; however, most studies
reporting these sorts of differences have examined only isolated
words, ignoring the fact that, in some languages, the same lexical
item can serve as either a noun or a verb depending on the context.
It thus remains unclear exactly what contribution representation
and processing make to word class differences.
Here, we investigated noun/verb representation and processing
differences by recording event related brain potentials (ERPs) from
individuals reading sentences one word at a time for comprehension.
We paired strictly Nouns (e.g., "beer"), strictly Verbs (e.g.,
"eat") and noun-verb class ambiguous words (Ambiguous NVs; e.g.,
"drink") with two, minimally-contrastive sentence contexts:
noun-predicting (e.g., "John wanted THE [target word] but ...") and
verb-predicting ("John wanted TO [target word] but..."). Even when
contextual information is available to completely determine whether
a word is being used as a noun or a verb, the response to class
Ambiguous NVs, relative to their unambiguous counterparts, is
characterized by a slow, frontal negativity from 200 ms into the
next word. There thus seems to be a representational difference
between word class ambiguous and unambiguous lexical items that
influences on-line processing independent of context. When placed
in inappropriate contexts, unambiguous Nouns and Verbs behave
similarly; both elicit a large central negativity (N400) followed
by a posterior late positivity, indicating that these items are
surprising and difficult to integrate under these conditions. When
used appropriately, however, the word classes differ in several
respects. For example, around 400 ms, Nouns -- as well as Ambiguous
NVs used as nouns -- elicit more fronto-central negativity than
Verbs or the same Ambiguous NVs used as verbs, respectively. This
contrast may reflect differences in the on-line predictability of
the two word classes in sentence contexts. In addition, Verbs
elicit a left, anterior positivity that is not observed to either
Nouns or to Ambiguous NVs used as verbs; this positivity is only
observed, however, when these unambiguous Verbs are used in
appropriate contexts. This suggests a clear representational
difference between the word classes, albeit one that interacts with
on-line processing constraints.
In sum, the results show clear evidence for representational
differences between nouns and verbs and between word class
ambiguous and unambiguous lexical items. The data also provide
evidence for word class processing differences and for interactions
between representation and processing.
Damasio, A. R. and Tranel, D. (1993). Nouns and verbs are
retrieved with differently distributed neural systems. Proceedings
of the National Academy of Sciences, 90, 4957-4960.
Gentner, D. (1981). Some interesting differences between verbs and
nouns.Cognition and Brain Theory, 4, 161-178.
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