Figure 2.

a. Rats preferentially revisited the chocolate location when it was about to replenish in Experiment 1. The probability of a revisit to the chocolate location in the first four choices of a test phase is plotted for replenishment and non-replenishment conditions. b. Rats used time of day, rather than information about remoteness, to adjust revisit rates in Experiment 2. The figure shows the difference between observed and baseline revisit rates. For the bar labeled interval, the baseline is the probability of revisiting chocolate in the afternoon. The significant elevation above baseline shown in the figure documents that the rats did not use remoteness or an interval mechanism. For the bar labeled time of day, the baseline is the probability of revisiting chocolate in the morning. The absence of a significant elevation above baseline is consistent with the use of time of day. The horizontal line corresponds to the baseline rate of revisiting the chocolate location in Experiment 1. Positive difference scores correspond to evidence against the hypothesis shown on the horizontal axis. c. and d. Rats preferentially revisited the replenishing chocolate location when the study, but not the test, time of day was familiar in Experiment 3. The probability of a revisit to the chocolate location in the first four choices of a test phase is shown for first replenishment and first non-replenishment sessions (c; initial) and for subsequent sessions (d; terminal). e. Rats remembered the time of day at which the study episode occurred in Experiment 4. Rats treated the novel study-test sequence as a late-session test phase, documenting memory of the time of day at study rather than discriminating time of day at test. The figure shows the difference between observed and baseline revisit rates. For the bar labeled test time, the baseline was the probability of revisiting chocolate in the test phase of the early session in Experiment 3. The significant elevation above baseline documents that the rats did not use the time of day at test to adjust revisit rates. For the bar labeled study time, the baseline was the probability of revisiting chocolate in the test phase of the late session in Experiment 3. The absence of a significant elevation above baseline is consistent with memory of the time of day at study. The horizontal line corresponds to the baseline revisit rate to the chocolate location from Experiment 3 (terminal). Positive difference scores correspond to evidence against the hypothesis indicated on the horizontal axis. a–e. Error bars indicate SEM. a, c, and d. The probability expected by chance is 0.41. Repl = replenishment condition. Non-repl = non-replenishment condition. a. * P < 0.001 difference between conditions. b. * P < 0.04 different from baseline. c and d. * P < 0.04 and ** P < 0.0001 difference between conditions. e. * P < 0.001 different from baseline. Reproduced with permission from Zhou, W., & Crystal, J. D. (2009). Evidence for remembering when events occurred in a rodent model of episodic memory. Proceedings of the National Academy of Sciences of the United States of America, 106, 9525–9529. ©2009 National Academy of Sciences, U.S.A.