Conflicting results in EEG alpha feedback studies

Success or failure of EEG feedback training for alpha enhancement can depend on how alpha activity is quantified and fed back. Alpha-enhancement failures usually employ a percent time(%) technique; successes typically use amplitude integration(e). To dramatize the differences between percent and integration techniques, we derived both measures simultaneously from left occipital(O 1 ) and left central(C 3 ) sites for 16 male subjects who were given 5.6 hours of integrated alpha feedback from the midline occipital(Oz ) site. At both the O 1 and C 3 sites the integrated and percent measures were not equivalent and not linearly related. Statistically significant differences in the(integrated, percent) correlation coefficients(z-transformed) were observed under the different recording conditions: alpha enhancement, alpha enhancement, alpha suppression, and baselines. Theoretical discussion of integration and percent techniques is given and the adoption of amplitude integration measures and feedback stimuli is strongly advocated.