Table 3.

Design of Experiment 3

Group	Phase 1	Phase 2	Phase 3	Phase 4	Test
BB–Few	4 AX→O	20 A→O	–	4 O→US	1 X
Control–Few	4 AX→O	20 B→O	–	4 O→US	1 X
BB–Many	4 AX→O	200 A→O	–	4 O→US	1 X
Control–Many	4 AX→O	200 B→O	–	4 O→US	1 X
BB–Many–Ext	4 AX→O	200 A→O	Ctx	4 O→US	1 X
Control–Many–Ext	4 AX→O	200 B→O	Ctx	4 O→US	1 X

Note—BB, backward blocking; Ext, extinction; A and B, complex tone and white noise, counterbalanced; X, click train; O, flashing light; US, footshock; –, no treatment; Ctx, context exposure for 2.5 h per session. The numbers denote the number of presentations of each trial type in each phase.