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Abstract:
During memory retrieval event-related potentials (ERPs) show
reliable positive differences between old (repeated) and new
stimuli under both intentional and incidental retrieval
instructions. Here, the electrophysiological correlates of both
types of memory retrieval were compared within a single task for
short-term repetitions of common words and famous faces.
Intentional and incidental retrieval were operationally defined as
repetitions of targets and nontargets in a modified Sternberg task.
Replicating previous work, two temporally and topographically
distinct memory potentials (revealed as difference potential
between the ERP of old and new stimuli) - a parieto-central
positivity between 300 and 600 ms and an earlier frontopolar
positivity between 200 and 400 ms - were observed. The early
frontopolar positivity was indistinguishable for both kinds of
retrieval but as compared to similar previous experiments where the
non-targets had been shown before, its amplitude was reduced. This
was caused by some ERP positivity present already at first stimulus
presentation, possibly related to encoding processes in the service
of subsequent nontarget recognition. In contrast, the late parietal
positivity was smaller for incidental than for intentional
retrieval for both words and faces. In addition, ERP
difference-waves for intentional and incidental retrieval differed
in scalp topography indicating contributions of different brain
systems. These results indicate that during the first few hundred
milliseconds after cue presentation, intentional and incidental
retrieval relate to similar neural activity; only thereafter do
they start to differ.
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