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Abstract:
ERPs were recorded with 61 electrodes from 20 students who
verified either the correctness of one-digit multiplication
problems or the semantic congruency of sentence fragments.
Multiplication problems varied in size and sentence fragments in
cloze probability. Semantic incongruencies evoked a typical N400
effect between 330 and 510 ms with a clear parieto-central maximum.
Arithmetic incongruencies evoked a negativity between 330 and 420
ms with a similar topography, but the maximum of this arithmetic
N400 was more circumscribed and during its descending flank the
center of gravity shifted towards left posterior positions. The
distinct topography implies that arithmetic and semantic
incongruencies are processed within partially distinct cortical
cell assemblies. Varying cloze probability modulated the amplitude
of the semantic N400 at centro-parietal electrodes between 300 and
390 ms. Numerically larger problems, in comparison to smaller
problems, evoked a negativity between 390 and 570 ms whose maximum
was located over the right temporal-parietal scalp. These results
suggest that the semantic incongruency and cloze probability effect
are functionally equivalent while the arithmetic incongruency and
problem size effect are functionally distinct. It is speculated
that the arithmetic and the semantic incongruency effects are both
related to a context dependent spread of activation in specialized
associative networks while the arithmetic problem size effect is
due to rechecking going beyond basic fact retrieval.
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