Schedule control of the vocal behavior of Cebus monkeys.

The team worked with three Cebus monkeys. They wanted to see if monkey calls could be turned into operant behavior.

Each call that met a sound goal earned a bit of applesauce. The researchers used simple FR 1 to FR 15 schedules first. Later they added VI, FI, and conjunctive schedules to one monkey.

The monkeys kept calling when calls produced food. Response rates matched the schedule rules, just like lever presses do.

One monkey even showed the classic scallop under FI and steady runs under VR. Vocal behavior, once shaped, followed the same laws as any operant.

Dews (1978) saw the same FI scallop in two monkeys working for food. Leander et al. (1972) now prove the pattern holds when the response is a call, not a lever press.

Fujita (1985) found that switching from continuous to FR kept discrimination accurate in Japanese monkeys. The new data extend that idea to vocal topography: intermittent ratio schedules also keep newly shaped calls alive.

Iversen et al. (1984) shaped grooming in vervets and showed natural behavior is not exempt from operant control. Leander et al. (1972) make the same point for vocalizations, closing the gap between instinctive calls and learned operants.

If monkey calls can be placed on FI, VR, or conjunctive schedules, so can early speech sounds in toddlers. You can treat first words like operants: reinforce close approximations on FR 1, then stretch to FR 5 or VI 10 to build endurance. The study reminds us that rate, rhythm, and wait-time are schedule effects, not mysterious traits. Pick the schedule that builds the pattern you want and shape the voice like any other response.