Do Chimpanzees Have Expectations About Reward Presentation Following Correct Performance on Computerized Cognitive Testing?

Abstract

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.De Waal (1991) described behaviors in chimpanzees that reflected the chimpanzees' sense of how others should or should not behave. He defined this sense for chimpanzees as "a set of expectations about the

What counts for ‘counting’? Chimpanzees, Pan troglodytes, respond appropriately to relevant and irrelevant information in a quantity judgment task

“…The results indicated that the chimpanzees performed at a high level and showed the signature ratio effects seen in other experiments that require relative quantity judgments by these apes (e.g. Beran 2001, 2004; Beran & Beran 2004). …”

“…Beran 2001, 2004, 2012; Beran & Beran 2004). In those tests, all items that were seen were relevant to the representations that the chimpanzees formed and used to choose between sets.…”

“…These chimpanzees had a long history of making quantity judgments of visual and auditory sets (e.g. Beran 2001, 2004, 2012; Beran & Beran 2004), although they had only limited experience in judging quantities that were spread among multiple locations within an array. In another experiment (A. Garland, M. J. Beran, J. M. McIntyre & J.…”

“…The most widely studied species are the nonhuman primates (e.g. Call 2000; Beran 2001, 2004; Anderson et al 2005, 2007; Hanus & Call 2007; Tomonaga 2007; Addessi et al 2008; Evans et al 2009; Mahajan et al 2009), all of whom show competencies in a variety of tasks that involve judging quantities, including auditory quantity judgments (e.g. Beran 2012) and even judgments between sequentially presented sets of items that can take a long time to complete (e.g.…”