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Abstract:
Abstract: We conducted a delayed matching to sample
experiment with 15 subjects. Stimuli were pac-men arranged to
either constitute a Kanizsa square or not. All stimuli were
presented at three different rotation angles. In a memory task,
subjects had to compare the rotation angle of the first (S1) and
second (S2) presentation. A random dot pattern was presented in the
variable delay between S1 and S2. In a perceptual control task,
subjects only had to tell whether the rotation was maxmimal for S2.
EEG was recorded from the 19 electrodes of the 10-20 system at 500
Hz. Individual frequency bands were analysed via a time-frequency
method using a wavelet approach. Alpha, beta and gamma bands were
investigated. We found increased evoked gamma activity for the
illusory figures as compared to non-illusory figures. In addition,
we found increased induced alpha activity in the delay for the
memory as compared to the control task. No differences were found
for evoked alpha. Consistent with previous findings reporting
event-related desynchronization in correlation with memory
processes (Klimesch, W.: EEG alpha and theta oscillations reflect
cognitive and memory performance: a review and analysis, Brain
Research Reviews 29, 169-95, 1999), the results suggest that the
alpha generators might be continuously active but vary in
synchrony.
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