Figure 1.

The physical layout of the large open experimental tank is shown on Panel A. This tank contained four stimulus tanks placed adjacent to the walls. All walls of the apparatus were made of glass and were transparent. One of the stimulus tanks contained five conspecific stimulus fish during training. Behind one of the stimulus tanks a red plastic cue card could be placed. The dimensions of the experimental tank along with the dimensions of certain areas of this tank are shown on Panel B. The areas shown with different shading served as a template for quantification of the location of the single experimental subject both during training and at a probe trial. The black areas represent the target zone that is proximal to the location of the stimulus. The gray areas represent the proximity zones which correspond to the target zone but are adjacent to stimulus tanks without the stimulus. The striped areas represent the stimulus tanks, and these areas are not accessible to the experimental fish. The white areas represent locations from which the content of the stimulus tanks are not possible to see due to reflection from the glass walls of the stimulus tanks (diffraction coefficient differences between glass and water). These latter two types of areas (striped and white) are excluded from the quantification and analysis of the location of the fish.