EEG Coherence and Amplitude Effects of Rhythmic Auditory and Visual Stimulation with an Emphasis in Computational Methods

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 subject’s 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 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. Two tables and eight figures are included. The Perl source code for 21 data analysis programs is provided, along with a tutorial chapter explaining how to use these algorithms in one's own research.