Performance in concurrent interval schedules: a systematic replication.

Smith et al. (1975) ran pigeons on two side-by-side keys. Each key paid off on its own variable-interval schedule.

The birds could hop and peck either key at any time. The team logged every peck and which key paid food.

They wanted to see if the birds’ response rates and time spent on each key matched the programmed payoff rates.

Response-rate ratios did not equal reinforcement ratios. Time allocation came closer, but still missed the mark.

The mismatch held for both fixed and variable interval schedules. The classic matching equation did not fit well.

Locurto et al. (1976) ran the same VI-VI setup and saw the same undermatching. Their power-function tweak to Herrnstein’s equation caught the curve better.

Pickering et al. (1985) later let birds work all day instead of short sessions. They saw overmatching—birds leaned even more on the richer key than payoff rates predicted. Same species, same schedules, opposite direction.

Renne et al. (1976) swapped pigeons for adult humans pressing buttons for money. People showed matching, not undermatching. The difference shows species and reinforcer type can flip the outcome.

When you set up concurrent schedules, do not assume response ratios will equal reinforcement ratios. Check both response count and time spent. If the client drifts toward one option too much, shorten the richer side’s interval or add brief extinction stretches to rebalance choice.