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Abstract:
Neuropsychological research showing that the regular
(jump-jumped) and irregular (drive/drove) past tense inflectional
morphology can dissociate following brain damage has been important
in testing claims about the cognitive and neural status of
linguistic rules. These dissociations have been interpreted as
evidence for two different computational systems - a rule-based
system underlying the processing of regulars and the irregulars
being individually listed in the mental lexicon. In contrast,
connectionist accounts claim that these dissociations can be
modelled within a single system. Combining behavioural data from
patients with detailed information about their neuropathology can,
in principle, provide strong constraints on accounts of the past
tense. In this study, we tested 5 Broca patients, all of whom had
extensive LH damage involving L inferior frontal gyrus and
underlying structures, and 4 HSE patients with semantic deficits
who had extensive damage to L inferior temporal cortex. These
patients were tested in experiments probing past tense processing.
In a large priming study, the Broca patients showed no priming for
the regular past tense but significant priming for the irregulars
(whereas controls show priming for both). In contrast, the HSE
patients showed significantly impaired performance for the
irregulars in an elicitation task. These patterns of behavioural
data and neuropathology suggest that two separable but
interdependent systems underlie processing of the regular and
irregular past tense.
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