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Abstract:
Investigations of regular and irregular morphology have been
central to the question of whether distinct systems subserve
grammar and lexicon (Pinker, 1991). On a dual-system view, regular
forms are computed by the application of a suffixation rule,
whereas irregular forms are retrieved from lexical memory. On a
single-system view, regulars and irregulars are computed in an
associative memory. Neurological double dissociations link regulars
to left frontal regions and irregulars to temporal/parietal regions
(Ullman et al., 1997). Magnetoencephalography (MEG) provides a
method to investigate the real-time spatio-temporal dynamics
associated with the production of regular and irregular past tense
forms. We asked seven right-handed men to produce past tenses,
given stems of 64 regular and 64 irregular verbs, while recording
from a whole-head 64-channel magnetometer. Satisfactory solutions
to the inverse problem of dipole fitting for data averaged over all
subjects were found at a number of 10 millisecond time-slices
following stimulus presentation. Dipoles in both the regular and
irregular verb conditions were localized to a left
temporal/parietal region (250 to 310 milliseconds). Dipoles in left
frontal regions were found only for regular verbs, for time-slices
immediately following the left temporal/parietal dipoles (310 to
330 milliseconds). The results are consistent with a dual-system
model in which temporal/parietal-based memory is searched for an
irregular form, whose successful retrieval blocks the application
of a frontal-based suffixation rule (Ullman et al., 1997).
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