Fig. 1. Sketch of apparatus with the patterned curtain in place along one side of the arena. Between each training trial, cylinders, starting pen (S) and feeder (F) were shifted en bloc to a new position along a 2.5 m line indicated by the broken line. The patterned curtain was only fixed in place during the experiment illustrated in Fig. 5. For the other experiments, all the curtains surrounding the arena were white.