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Abstract:
Event-related potentials (ERPs) were employed to investigate
the brain activity elicited during the anticipation of episodic
versus semantic memory tasks. At study, subjects performed a 'deep'
encoding task (sentence generation) on visually presented words,
and at test, they carried out either episodic (old/new recognition)
or semantic (animate/inanimate) judgements on a mixture of studied
and unstudied items. The test task was varied randomly from trial
to trial, its nature being indicated by a cue that signalled
whether the following item should be subjected to a recognition or
animacy judgement. At frontal electrode sites, the ERPs elicited by
these cues varied according to the nature of the signalled task,
and also whether the cue indicated the continuation of, or switch
from, the task set established on the preceding trial. Over left
frontal sites, the slow potentials developing between the cue and
the test item were more positive-going for the episodic than for
the semantic task. This effect was present regardless of whether
the same task had been performed on the previous trial. Over right
frontal sites, however, this task effect was more marked for same-
than for different-task trials. The findings are consistent with
the view that episodic and semantic retrieval are associated with
different task sets, and that these sets are supported by frontal
brain regions. In addition, the findings point to a hemispheric
asymmetry in the dynamics of set switching.
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