STIMULUS ASPECTS OF AVERSIVE CONTROLS: STIMULUS GENERALIZATION OF CONDITIONED SUPPRESSION FOLLOWING DISCRIMINATION TRAINING.

Pigeons pecked for food while tones sounded. Some birds got tone-shock pairings with no other training. Others first learned to tell two tones apart: one tone meant shock, the other did not. The team then played many new tones to map how much each bird slowed its pecking. They drew a picture of the fear spread across tone frequencies.

Birds that only heard one tone showed a smooth, symmetrical dip in pecking around that tone. Birds taught to tell tones apart showed a lopsided curve; fear bled more toward tones near the shock cue. No bird showed peak shift; the strongest suppression stayed at the trained shock tone, not beyond it.

HOFFMAN et al. (1963) showed these fear curves can last 2.5 years but keep fading with each test. The 1964 lab added the twist that teaching a discrimination skews the curve in the first place. Hoffman et al. (1966) later trained birds with two shock tones and saw a twin-peaked curve, proving the asymmetry can stack. Okouchi (2003) moved the same skewed shape to college students looking at line lengths, showing the pattern crosses species and senses. Powell et al. (1968) found more discrimination reps make the curve even steeper, giving a practical rule: extra S+/S- sessions sharpen stimulus control.

When you run punishment or fear-reduction programs, remember that prior discrimination training changes how fear spreads. If a client already tells two cues apart, new cues close to the aversive one may trigger stronger avoidance than you expect. Test generalization probes on both sides of the trained stimulus and add extra discrimination trials if you need tight stimulus control.