Six of the 12 animals were used for testing at each retention interval. Each animal was assigned randomly to participate in training and testing for three of the six retention intervals (+ symbols in each column). For each retention interval, the six animals that were used were assigned randomly to receive either the CS+ or the CS– training and its associated test procedure first. Two weeks after that procedure was completed the animals received the reverse training and testing procedure. At least 6 weeks passed between testing at each retention interval