Fig. 1. Experimental room A and apparatus in experiment I. The rectangular room (567 cmx433 cmx220 cm) contained two arenas (diameter: 220 cm) that were equipped with a peripheral nest box. The short walls were either white or black with a grey margin, and the long walls were covered with two-dimensional landmarks. Three landmark objects were located between the two arenas. Normal room lighting was provided by lamps at floor level. An infrared video camera that was surrounded by a ring of infrared diodes (peak emission, 940 nm; bandwidth, 45 nm) was mounted on an optic bench and moved above the centre of the arena where the animal was being tested.