Testing for inhibitory stimulus control with S- superimposed on S+.

Blough (1971) worked with pigeons in a lab. The birds pecked a key when a green light was on. The green light meant food would come. The team then placed a red light on top of the green light. Red meant no food. They wanted to see if the red light would stop pecking and create a smooth drop-off in responses.

The red light did stop most pecking. But the drop was all-or-none. There was no smooth gradient. The birds either pecked a lot or almost none. The red light acted like a switch, not a dial.

Winett et al. (1972) ran a near-copy study the next year. They also saw that a red extinction cue cut observing to zero. Both papers agree: S- shuts things down.

Hamm et al. (1978) later showed the opposite pattern. When they stacked two good cues, response rates added up. Good cues combine; bad cues override.

Locurto et al. (1980) extended the idea to adult humans. In their lab, people actually pressed keys to see the red extinction cue. The same red light that repelled pigeons attracted people. Species and procedure matter.

When you add a negative stimulus, expect a quick stop, not a slow fade. This tells you to check for all-or-none drops in your data. If you need a smooth reduction, use many small steps instead of one big S-. Also, watch for species differences: kids might look at the very cue that shuts down a pigeon.