Table 1. The VI schedules presented on the target alternative and their associated discriminative stimuli.

Presentation group	VI (s)	Discriminative stimuli
A	6	Red light flashed on for 0.5 s and off for 0.2 s
	14	Yellow light flashed on for 1.0 s and off for 0.5 s
	55	Green light flashed on for 1.5 s and off for 1.0 s
	100	Red and yellow lights flashed on for 2 s and off for 0.5 s
	450	Red and green lights flashed on for 2 s and off for 1 s
B	10	All lights flashed on and off at 0.2-s intervals
	20	All lights flashed on and off at 0.5-s intervals
	45	All lights flashed on and off at 0.75-s intervals
	200	All lights flashed on and off at 1.5-s intervals
	350	All lights flashed on and off at 2.5-s intervals