Comparisons between variable-interval and fixed-interval schedules of electric shock delivery.

Scientists compared two ways of giving mild electric shocks to rats. One group got shocks on a fixed-interval schedule. The other got shocks on a variable-interval schedule.

They also tested what happens when a 5-second light comes on before each shock. They measured how much the rats kept pressing a lever for food during these schedules.

Fixed-interval shocks stopped the rats from lever-pressing more than variable-interval shocks. The light warning helped reduce this suppression.

The warning worked differently on fixed versus variable schedules. Fixed-interval schedules with warnings still suppressed more responding than variable ones.

Byrd (1972) looked at fixed versus variable intervals too, but with food rewards instead of shocks. They found choice patterns that set the stage for this shock study.

Renne et al. (1976) and Winett et al. (1991) both tested variable-interval schedules with humans getting money or warmth. Their results show these schedule effects work across species and reinforcer types.

Locurto et al. (1976) found pigeons undermatch reinforcement rates on variable-interval schedules. This helps explain why variable shocks suppress less - the timing is harder to predict.

This tells us predictable aversive events suppress behavior more than unpredictable ones. When you must deliver corrections or negative consequences, make them less predictable in timing. Add warning stimuli when you need to reduce the suppressive effect. This matters for behavior reduction procedures and compliance training.