Table 2.

Design Summary of Experiment 2

Group	Conditioning	CS Duration (sec)	US-US Interval (sec)	Test
Acq-Long	X→US (8)	250	650	X
Acq-Partial	X→US (8) / X (72)	25	650	X
Acq-Spaced	X→US (8)	25	650	X
Acq-Massed	X→US (8)	25	65	X
OV-Long	AX→US (8)	250	650	X
OV-Partial	AX→US (8) / AX (72)	25	650	X
OV-Spaced	AX→US (8)	25	650	X
OV-Massed	AX→US (8)	25	65	X

Note—Acq, elemental acquisition control; OV, overshadowing; Long, conditioning with CS of long duration; Partial, conditioning with CS of short duration on 10% partial reinforcement schedule; Spaced, conditioning with CS of short duration; Massed, conditioning with CS of short duration with short US-US interval; X, target cue; A, overshadowing cue; US, footshock unconditioned stimulus; “→,” sequential pairing of stimuli. CS X was a click train and CS A was a complex tone for all subjects. Numbers in parentheses refer to the number of each trial type.