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Presentation
Abstract - Jon Frederick, Ph.D.
The photic driving response, the effect
of a flashing light stimulus on the cortical EEG, has proven to be a
sensistive neurometric that varies with differences in perception, mood,
and physiological states. The diverse effects of photic stimulation have
made commercially available "brainwave syncronizers" popular
among consumers and even among some clinicians. It is common in the
design of these devices to combine a
rhythmic auditory stimulus with the visual stimulus. However, little if
any experimental evidence supports the assumption that auditory
stimulation enhances the photic driving effect. Therefore, this study
compared the amplitude and coherence effects of three stimulation
conditions (all sinusoidally-modulated): visual stimulation alone,
auditory stimulation alone, and combined auditory and visual stimulation
(AVS) at each subject's peak alpha frequency (PAF), in 30 college
students, using the standard 10-20 19- electrode montage. An eyes-closed
baseline EEG determined each subject's PAF. The three 5-minute
stimulation conditions were then administered in a randomized,
counterbalanced order, while EEG was recorded. A four minute eyes-closed
poststimulation baseline was recorded after each stimulation condition.
Amplitude and coherence values were calculated for 1-2 Hz, 2-4 Hz, 4-8
Hz, 8-12 Hz, 13-21 Hz, and
21- 32 Hz, and for the 1.5-Hz band surrounding each subjects PAF. Visual
stimulation or combined AVS significantly increased EEG amplitude at the
PAF, 8-12 Hz, 13-21 Hz, and 21-32 Hz.
Auditory stimulation alone had
negligible effects on amplitude, and did not result in significant
differences in amplitude between the visual and combined AVS condition.
Similarly, the auditory stimulus had only chance-level effects on EEG vi
coherence, while the visual alone and combined AVS conditions evoked
significant changes in coherence across the spectrum. However, the
interaction between auditory and visual stimulation resulted in
significant differences between the visual alone and combined AVS
conditions. No residual effects of stimulation on amplitude or coherence
were observed in the four minute recordings following each of the three
stimulation sessions.
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