Concurrent fixed-ratio and avoidance responding in the squirrel monkey.

Scientists placed squirrel monkeys in a box with two levers.

One lever paid food after every 20 presses (fixed-ratio 20).

The other lever postponed a mild shock if the monkey pressed at least once every 5 s (avoidance).

The team ran both schedules at the same time and later removed one to see if the other changed.

Taking away the food lever did not speed up or slow down shock-avoidance presses.

Taking away the shock lever did not change food-lever speed.

Each schedule kept its own rate, showing independence.

FIELPREMACK et al. (1963) saw the same independence in chimpanzees juggling four schedules.

Tantam et al. (1993) found a different story with people: adding TV or reading changed how humans performed on a fixed-interval task.

The monkey data say "schedules run alone"; the human data say "concurrent activities matter." The gap is species, not science.

Najdowski et al. (2003) later showed pigeons swap preferences fast when delays change, proving concurrent schedules can talk to each other when the payoff shifts.

If you run two protocols at once—say, DTT plus escape extinction—watch each graph separately. This study says one program can hold steady while the other is paused or modified, as long as the reinforcers do not overlap. Use this to stagger changes without risking a total behavior drop.