Stimulus control of temporally spaced responding in second-order schedules.

Rees et al. (1967) asked a simple question. If you break a DRL schedule into two parts, does it matter where you place extra lights or sounds?

They ran rats on second-order DRL. Each cycle had an early half and a late half. The team tried three set-ups. In the tandem version, nothing changed. In the chained version, a new light came on only for the early half. In the brief-stimulus version, a quick flash marked the end of the early half.

The extra cues did not just decorate the box. They moved the response rate.

Chained light = fewer presses in the early half. Brief flash = more presses in the early half. Same food at the end, but the middle looked very different.

Hamilton et al. (1978) later copied the brief-stimulus set-up and also saw higher early rates. They added an unpaired control and proved the flash works because it is paired with food. The 1967 mixed result now makes sense: the flash acted like a tiny conditioned reinforcer.

Berler et al. (1982) showed the same process in plain DRL. A 20-s tone that only signaled upcoming food lifted pressing that the schedule had suppressed. Together, the three papers show external cues can either brake or gas pedal DRL behavior depending on how they link to payoff.

MOLLIVER (1963) had already sharpened DRL timing by inserting a separate lever that produced its own click. The 1967 study widened the idea: you can insert cues instead of extra responses and still move the pattern.

When you chain or mark parts of a schedule, you are not just being fancy. You are adding mini reinforcers that can speed or slow the next response. If a client rushes through a wait period, try inserting a brief praise or token at the halfway point and watch the pace. If they drag too slowly, remove the midway cue or keep the room neutral until the final reinforcer. One small stimulus move can flip the whole rate.