The ultrasound speakers in the tank are the small black spheres. There are one or two such speakers in different experiments. The speaker used in the sonic range is the light blue disc, and was not used in all of the experiments. The round light source is mounted in the center of the tank. An AC-LED is located on top of this light and id used to indicate stimulus onset and offset. The experimental tank also were the holding tanks in order not to have to move the experimental animals. Thus, there are several pieces of equipment in the tank to help maintain the animals. This included green air stones and parts of the filter. In order not to disturb the fish the filter and air stones were left in place during experiments, but they were turned off (and on) as control to assure that they did not impact the bahavior of the fish in response to sound stimuli. No difference in behavior was detectable if these items were switched on or off. Two ultrasound hydrophones were used in some experiments and they were located on opposite sides of the tank. In experiments where the two hydrophones were involved, they were in random order. The sonic speaker was used in noise experiments. To test responses to white noise we only used sonic speaker, and this was played for several minutes. During masking experiments the sonic hydrophone was placed either directly behind the ultrasound hydrophone or on the opposite side. In both cases, no difference in behavior were observed. Click on the figures below to enlarge the figures.

	Standard experiment 1 = filter outlet 2 = air supply 3 = central light 4 = ultrasound hydrophone 5 = stimulus LED (flashing)

	Directional experiment 1 = ultrasound hydrophone(2) 2 = stimulus LED 3 = central light 4 = airsupply

	Noise experiment 1 = filter outlet 2 = stimulus LED 3 = air supply 4 = central light 5 = sonic hydrophone 6 = ultrasound hydrophone