TABLE 1.

Experimental designs.

Experiment	Group		Conditioning	Retardation test
EXP1	14-2	Experimental	14A+ / 12F− / 2AX− / 2X−	10X+
		Control	14A+ / 12F− / 2BX− / 2X−	10X+
Exp2	8-8	Experimental	8A+ / 6F+ / 6F− / 8AX− / 2X−	10X+
		Control	8A+ / 6F+ / 6F− / 8BX− / 2X−	10X+
Exp3	5-11	Experimental	5A+ / 9F+ / 3F− / 11AX− / 2X−	10X+
		Control	5A+ / 9F+ / 3F− / 11BX− / 2X−	10X+

A represents tone presentation, B represents light presentation, AX represents tone-click compound presentation, F represents lever presentation and X represents click presentation. The numbers before the letters indicate the number of trials that the stimulus was presented in each session. The + symbol represents that the stimuli were followed by a food pellet and the − symbol represents that the stimuli were not followed by a food pellet.