Interactions in multiple schedules with different responses in each of the components.

Scull et al. (1973) worked with pigeons in a two-key box.

Each key used a different schedule. One key gave food on a variable-ratio plan. The other key gave food on a variable-delay plan.

The twist: in some sessions the birds pecked the same key for both schedules. In other sessions they pecked one key for the first schedule and the second key for the other schedule.

When the birds used the same peck for both schedules, positive contrast showed up. Rates in the richer component rose above baseline.

When the birds used different pecks, most birds slowed down instead. Positive contrast almost vanished.

The form of the response—not just the schedule—decides whether you see contrast.

Kaufman (1965) first showed contrast in multiple schedules, but kept the same response. J et al. added the topography twist: change the move, change the effect.

Davol et al. (1977) later pinned negative contrast on long pauses. They kept one response and tweaked timing rules. Together the papers show contrast has two knobs: response shape and pause length.

McLean et al. (1981) tracked moment-by-moment rates. They found the biggest shifts right after a component switch. J et al. did not look at time, so the 1981 study adds a clock to the topography rule.

If you run multiple schedules in therapy—say, DRL during reading and VR during math—keep the topography alike if you want rates to rise in the richer part. Switching from tapping to vocal replies can kill the boost you expect. Check your response forms before you blame the schedule.