| |
Abstract:
We examined psychophysiological parameters (ERP, fMRI) in a
number reduction task. The task was to reduce an eight digit string
to a seven digit string by applying a set of given rules.
Participants were asked to enter seven digits one by one, or enter
the final relevant digit. The hidden rule was that the last digit
in the reduced string was always identical to the second entered
digit. Participants performed 7 blocks of 36 trials. 10 subjects
("explicit group") developed explicit access to the hidden rule
indicated by an abrupt change in the number of responses (i.e.
entered the final digit after the second one). The performance of
the remaining 10 subjects improved only by implicit learning
indicated by RT decreases for all responses. ERPs were calculated
for whole trials and for each input. For the trial-locked ERP,
parietal and frontal P3 amplitudes decreased over blocks. The
explicit group showed a larger frontal P3 from the beginning of the
experiment on, i.e. even before changing their strategy. Further
analyses of single input ERPs revealed larger frontal positive
components in the explicit group for the first inputs which
determined the final result, especially in the block preceeding the
strategy change. These results suggest that explicit memory was
generated independently of an implicit learning process.
|
