Conditional discrimination of electroencephalogram alpha amplitudes in humans.

Conditional discrimination of high and low alpha amplitudes of electroencephalogram by humans was demonstrated in the 1950s. Despite several attempts, the original finding was only replicated once, but discrimination accuracy in the replication was only slightly above chance level and confounds may have contributed to it. Potential confounds included a systematic difference in time to exceed thresholds for high and low amplitudes (i.e., temporal cue), unequal numbers of high- and low-amplitude trials, and short trial durations that allowed for correct choices in a preceding trial to serve as a cue for the next trial due to gradual shifts in alpha amplitude. In the current study, we modified the procedure for eliminating these confounds: Participants observed a bar motion corresponding to changes in alpha amplitude for a constant duration. The direction of the bar motion (up and down) was positively or negatively correlated with the amplitude depending on the trial, and the participant's task was to discriminate the two types of trials. Three of five evaluable participants (60%) showed alpha discrimination without the above confounds, and this success rate was similar to that reported in the original study. Thus, alpha discrimination appears to be a replicable phenomenon.