Table 1.

Design of Experiment 1

	Phase 1		Phase 2
Group	Training (Context A)	ITI	Extinction (Context B)	ITI	Test (Context B)
Control	4 X→US	120	context only		X
Massed	4 X→US	120	20 X	6	X
Intermediate	4 X→US	120	20 X	120	X
Spaced	4 X→US	120	20 X	600	X

Note—X was a clicker CS, and US was a footshock. Numbers next to pairings denote the numbers of trials. ITI, intertrial interval, in seconds, for acquisition and extinction trials. The massed and intermediate groups were subdivided into subgroups that experienced trials early or late in the extinction session, which was 220 min long.