Each of 4 aquariums was housed in a small room that was acoustically and visually isolated from the handle equipment. Ambient light in the room was programmed on a 12 hr light/dark cycle. During each consultation, the ambient light was on. Temperature and humidity in the room were held constant. An instance of the equipment is diagrammed in Figure 1 all letter references during this description are to this figure. Each aquarium was 20.