Recent findings substantiate the view that electroencephalographic (EEG) al
pha rhythm (7-13 Hz) is functionally involved in cognitive stimulus process
ing. Our previous results have shown that enhanced alpha responses to audit
ory task stimuli can be well synchronized with stimulus until 800-1000 ms.
The present study analyzed the effect of perceptual uncertainty and difficu
lty in decision making on event-related alpha oscillations in single audito
ry event-related brain potentials (ERPs). EEG was recorded from Fz, Ct and
Pt electrodes in 10 subjects participating in two experimental sessions, in
which auditory stimuli with equal physical parameters were presented under
passive and task instructions. Separate measurements of single alpha respo
nse amplitude and phase-locking were performed and statistically analyzed f
or consecutive time windows in the post-stimulus epoch. Major results show
that, during the cognitive task, the phase-locking of alpha oscillations at
the frontal site is significantly increased in the time window of 500-1000
ms after stimulation. Thus, the involvement of enhanced and synchronized f
rontal alpha activity in higher brain processes is strongly emphasized. (C)
2001 Elsevier Science B.V. All rights reserved.