Apparatus
Rats were carried in individual acrylic boxes on a cart between the vivarium and one of the two experimental rooms that represented different contexts. One context consisted of 8 adjacent wire cages (20 cm long, 14.5 cm wide, 15 cm high)on steel cabinets in a dark room with a 1.67-Hz xenon strobe flasher (Sun Beamer BC-100, Taiyo Giken Co., Japan) placed 60 cm above the cages. A continuous noise (approximately 68 dB re Scale C) was delivered by an FM radio tuned away from any station. Liquid (tap water or salty water) was provided to each rat from a glass bottle with a white-painted metal spout inserted from the cage ceiling: the end of the spout was at a distance of 4 cm from the cage ceiling. The other context consisted of 8 transparent plastic cages (40.5 cm long, 24.5 cm wide, 17 cm high) with wood-shaving bedding (2 cm thick)and wire lids. They were located on the floor of a quiet room continuously lighted by fluorescent lamps on the ceiling. Fluid was supplied to each rat from a glass bottle with a black-painted metal spout inserted from the cage ceiling; the end of the spout was at a distance of 4 cm from the cage ceiling. These 2 physical contexts were counterbalanced within each group with regard to their functional roles as Contexts A and B.