The effect of multiple S-delta periods on responding on a fixed-interval schedule: 3. Effect of changes in pattern of interruptions, parameters and stimuli.

Pigeons pecked a key on a fixed-interval 5-min schedule. Food arrived only for the first peck after 5 min passed.

During each interval the experimenter turned the lights off for several short S-delta periods. The birds could not earn food while the lights were out.

The birds still showed the smooth scallop shape: low pecks early, fast pecks near food time. Extra dark periods did not flatten the curve.

The pattern stayed the same no matter how many or how long the S-delta breaks were. The schedule itself, not steady mediating behavior, controlled the timing.

Palya (1993) extended the idea. He mapped different colored lights to early, middle, and late parts of the same fixed interval. Early colors acted like negative reinforcers and late colors like positive reinforcers, showing that time within the interval gives stimuli their power.

O'leary et al. (1969) used second-order schedules where brief food-paired flashes marked the end of small FI parts. The flashes kept the scalloped pattern even when real food was far away, echoing DEWS (1965) that brief cues can hold the shape.

Iversen et al. (1984) looked at schedule-induced activity instead of key pecks. Visual cues signaling food versus no-food periods controlled the extra movement, broadening the rule: schedule-linked stimuli guide many kinds of behavior.

You can stop worrying that every second must be filled with reinforcement. Brief breaks, room lights off, or short extinction periods will not wreck the timing your learner has built. Use clear signals for when reinforcement is possible and when it is not, then trust the schedule to keep the rhythm.