IN THE NORMAL electroencephalogram the alpha potential is a fairly regular 8- to 13-cps rhythm, which is best obtained from the occipital leads and is most prominent in the waking, but resting, state. It is normally promptly suppressed by visual attention, such as is produced by flashing a light in the subject's eyes. It can also be blocked by any sufficiently forceful stimulus requiring alertness and attentiveness, such as a loud sound or the solving of a difficult mathematical problem. However, except for these forceful stimuli, the blocking of the alpha potential is fairly specific for visual effects and does not normally respond, for example, to sounds of low intensity. Therefore, at least within a certain range of intensity, the alpha blocking to visual stimuli is a specific inborn, or unconditioned, response.
Study of the conditioned alpha rhythm in man began in 1936, when Loomis, Harvey, and Hobart,1 as