Table 2. Design Summary of Experiment 2.

Group	Phase 1	Phase 2	Phase 3	Baseline	Test X
Inhib-AX	32 AC/32 BC	12 A-US/12 B-US	6 AX-US	7.75	cr
Inhib-ABX	32 AC/32 BC	12 A-US/12 B-US	6 ABX-US	8.00	cr
None-AX	32 AD/32 BC	12 A-US/12 B-US	6 AX-US	6.92	cr
None-ABX	32 AD/32 BC	12 A-US/12 B-US	6 ABX-US	8.50	Cr
Excite-AX	32 AB/32 CD	12 A-US/12 B-US	6 AX-US	7.67	cr
Excite-ABX	32 AB/32 CD	12 A-US/12 B-US	6 ABX-US	7.75	CR

Note—CSs A, B, C, and D were white noise, tone, flashing light, and buzzer presentations, counterbalanced within groups as completely as possible. CSs A, B, C, and D were 10 sec in duration during Phases 2 and 3, but 60 sec during Phase 1. CS X was a 10-sec click train. The US was a 0.5-sec, 1.0-mA footshock. Slashes denote interspersed trials within sessions. On the basis of simulations of ECH, CR, Cr, and cr denote strong, intermediate, and weak levels of expected conditioned responding. Baseline = mean number of leverpresses emitted across the 30-sec, pre-CS period prior to the first target stimulus presentation during the test session.