Conditioned reinforcement in chimpanzees.

Abstract

After training 2 chimpanzees to lever-press on a 5-minute fixed-interval schedule of food reinforcement, they were trained to obtain food by inserting poker chips through a slot. Given opportunity to lever-press on the same reinforcement schedule for poker chips (exchanged for food at end of each hour) both animals responded to initial low rates and eventually failed to respond. In a second experiment the animals were required to accumulate groups of chips before exchange, the number being gradually increased (2, 3, 4, 6 and 8 chips). Response rates were directly related to temporal proximity of exchange for food, becoming irregular when 6 chips were required and extinguishing when 8 chips were required.