Figure 1.

Screenshots (a,c) of apparatus and schematic representations of individual arenas (b). (a) The set-up consists of a single arena. Ethovision detects the presence of a subject in the left or right zones (indicated by shaded boxes), which sit 1 cm in front of the stimulus windows. (b) The arena is divided into three adjoining compartments. The central compartment is 8 cm long and 6 cm wide, with the 8 cm sides being clear for viewing the stimulus compartments. Each stimulus compartment is divided into eight 1.5 cm long and 1 cm wide opaque sections. At the beginning of the trial, the subject is held in a removable transparent cylinder with a 2 cm diameter. A removable opaque barrier was present between the stimulus fish and test fish. (c) Schematic of ‘controlled space’ conditions with the white dots representing the positions of the outermost zebrafish in a controlled 2 versus 4 contrast. (Online version in colour.)