In 1935, Durup and Fessard1 reported studies on the response of alpha waves to visual stimulation. They used a camera to photograph changes in alpha activity at the appearance of a bright light. The click associated with opening the camera shutter had no effect by itself on the alpha activity. When, however, the click was presented in conjunction with light, after a few such temporal associations the click began to cause disappearance of alpha activity, just as had the light. If the click were then presented several times without visual reinforcement, it ceased to affect the alpha activity. Durup and Fessard interpreted this observation to indicate the development of a conditioned reflex—i.e., an auditory stimulus (the conditioned stimulus), which previously had no effect upon the alpha activity, had by its temporal association with the light (the unconditioned stimulus) acquired the ability to effect disappearance of the alpha activity. A