To investigate whether 2 chimpanzees had expectations regarding the outcome of their responses on a computerized task, food reward that typically was given for correct responses was withheld on some correctly completed trials. There were two types of these probe trials: those which the chimpanzees performed correctly on their own, and those during which the chimpanzees needed the experimenter's assistance to complete the trial correctly. For both chimpanzees, reward procurement behaviors directed toward the experimenter occurred significantly more often on correctly completed probe trials than on incorrectly completed trials. This indicated increased expectation of food reward on correct trials as compared to incorrect trials. For 1 of the 2 chimpanzees, reward procurement behaviors were significantly more likely to occur on probe trials on which the chimpanzee received no assistance from the experimenter than on trials in which the experimenter assisted the chimpanzee. This behavioral difference was not predicated on reinforcement history, as all correctly completed nonprobe trials were rewarded whether or not assistance was provided by the experimenter. These data indicate that this chimpanzee may have a rudimentary sense of "equity" regarding what outcome should accompany the successful completion of trials that is dependent on the level of assistance provided by an experimenter during the trial.
Beran, M. J. (2001). Do chimpanzees have expectations about reward presentation following correct performance on computerized cognitive testing? Psychological Record, 51(2), 173-183. Available at: http://opensiuc.lib.siu.edu/tpr/vol51/iss2/1/