On some causes of behavioral contrast.

Researchers worked with pigeons on a two-part schedule. In one part the birds earned food on a low-rate DRL. In the other part they earned food on a variable-interval schedule.

The team added bright lights and noise each time a pigeon pecked too soon on the DRL. They wanted to see if this extra feedback would stop the early pecks and also create behavioral contrast.

The feedback cut the pigeons’ early pecks and earned them more food in the DRL part. Yet their peck rate still rose in the unchanged VI part.

Contrast showed up even though the DRL now delivered more reinforcers, not fewer. This told the field that contrast can happen without a drop in reinforcement.

Thomas et al. (1974) later showed the opposite: when they kept response rates the same but lowered reinforcement in one part, contrast still appeared. Together the two studies prove that neither lower reinforcement nor lower response rate is required for contrast.

Rogers-Warren et al. (1976) looked like they disagreed. They equated reinforcement across parts and saw no contrast. The gap is explained by method: S et al. added stimulus feedback, which may have worked like a mild punisher. That extra variable let contrast emerge even with richer reinforcement.

Hineline et al. (1969) added that the next schedule part matters. Contrast grows if the upcoming part switches to extinction. Clinicians should watch both the current and the upcoming contingencies.

If you run multiple schedules or DRL with clients, remember that adding feedback can boost reinforcement in one activity yet still drive contrast in another. Track response rates across both settings, not just the one you changed. When you see a sudden jump in the unchanged part, check whether extra feedback or richer reinforcement in the other part is acting like a punisher or a distractor.