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Abstract:
Abstract: Leipziger Strasse 44, 39120 Magdeburg, Germany
Square, London EC1V 0HB, England Combined direct-current EEG and
MEG recordings were obtained from 9 healthy subjects during a
word-stem completion test. In the intentional condition stems were
to be completed with previously studied words. In the incidental
condition stems were to be completed with the first word coming to
mind. In both conditions subjects judged whether or not the
completed word was presented in the study list. With both EEG and
MEG a sustained (2 seconds) late right-frontal shift (positive in
EEG) distinguished intentional from incidental retrieval. This
shift occurred in comparisons involving stems corresponding to both
studied and unstudied words. Earlier posterior retrieval effects
(i.e., the parietal old/new effect) were dissociated from the
right-frontal effect either by showing no difference (unstudied
items) or a difference with opposite polarity (studied items). The
data suggest that right-frontal activity as observed here reflects
episodic retrieval mode, whereas posterior activity is linked to
retrieval success. They are separable in that they show a double
dissociation in the brain-activity pattern for studied and
unstudied items during intentional and incidental retrieval.
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