Figure 2.

Extinction training as a function of stimulus length, repetition, and predictability. A, Experimental schedule depicting that B6N mice received a single tone–shock pairing at d0 and were subsequently exposed to one of three tone presentation protocols at d1 and d2, followed by a final 20 s tone presentation at d3 (n = 10 per group). B, Development of the total freezing responses over the course of repeated extinction training. C, Development of the freezing responses over the course of tone presentations per day (note that freezing to the 200 s tone was analyzed in 20 s bins). D, Development of the freezing responses to the initial 20 s of tone presentations per day. The duration of freezing was normalized to respective observation periods and presented as the mean ± SEM. Results of the two-way ANOVA for repeated measurements with the main factors protocol (P) and time (T) are shown in the graphs (for the sake of clarity, we do not report the results of post hoc analyses).