Responses to quantity: Perceptual versus cognitive mechanisms in chimpanzees (Pan troglodytes).

Abstract

Two chimpanzees were trained to select among 2 different amounts of candy (1-6 items). The task was designed so that selection of either array by the active (selector) chimpanzee resulted in that array being given to the passive (observer) animal, with the remaining (nonselected) array going to the selector. Neither animal was able to select consistently the smaller array, which would reap the larger reward. Rather, both animals preferentially selected the larger array, thereby receiving the smaller number of reinforcers. When Arabic numerals were substituted for the food arrays, however, the selector animal evidenced more optimal performance, immediately selecting the smaller numeral and thus receiving the larger reward. These findings suggest that a basic predisposition to respond to the perceptualmotivational features of incentive stimuli can interfere with task performance and that this interference can be overridden when abstract symbols serve as choice stimuli. Evaluation of numerical capabilities in animals in recent years has expanded the range of skills previously demonstrated in nonhuman species, provoked new questions regarding possible processing mechanisms that might subserve these capacities, and encouraged new directions for research (Boysen & Capaldi, 1993; Thomas & Lorden, 1993). Findings from our laboratory have indicated that the chimpanzee is an apt subject for the study of numerical competence and, with appropriate training, can demonstrate facility with counting, basic summation abilities, symbolically mediated summation, and an understanding of

Do cleaner fish learn to feed against their preference in a reverse reward contingency task?

“…Does the reverse reward task test for "self control"? Initially, studies on impulse control were mainly performed with humans (Mischel et al 1989;Russell et al 1991) and primates (Boysen and Berntson 1995;Boysen et al 1996;Silberberg and Fujita 1996;Kralik et al 2002;Genty et al 2004). Some authors have suggested that success in the reverse reward task may be interpreted as a form of "self control" thereby implying that in order to solve the task, some "awareness of self" needs to be involved (e.g.…”

“…Finally, after the surprising Wnding that many primates have diYculties in refraining from the larger amount in order to obtain a small one (Boysen and Berntson 1995), many subsequent studies focussed on procedures that help the test subjects to overcome this problem. However, this approach may distract from an important question, i.e.…”

“…When the subject reaches or points towards one quantity, the non-selected quantity is given as the reward. Many species such as chimpanzees, Pan troglodytes (Boysen and Berntson 1995), Japanese macaques, Macaca fuscata (Silberberg and Fujita 1996), squirrel monkeys, Saimiri sciureus (Anderson et al 2000), cottontop tamarins, Saguinus oedipus (Kralik et al 2002), rhesus macaques, Macaca mulatta (Murray et al 2005) and two species of prosimians, black and brown lemurs, Eulemur fulvus and E. macaco (Genty et al 2004) showed an initial preference for the larger quantity of food. Such discrimination between two quantities of food could also be shown in red-backed salamanders (Plethodon cinereus) (Uller et al 2003).…”

“…Given that other complex cognitive abilities including numerical skills, symbolic representation, and other higherorder information processing capacities had already been shown in chimpanzees, failure in the reverse reward test was especially surprising in the initial study in chimpanzees (Boysen and Berntson 1995). As a result, many subsequent studies focused on developing procedures that could overcome the problem of failure in this task.…”

“…As a result, many subsequent studies focused on developing procedures that could overcome the problem of failure in this task. In some species that failed to choose the non-preferred reward in order to obtain the preferred one, cues such as Arabic numerals for chimpanzees and colour cues for cottontop tamarins associated with the two quantities of food enabled the species to succeed (Boysen and Berntson 1995;Kralik et al 2002). DiVerences in performance when testing the subjects with food only or with Arabic numerals have been interpreted to result from a conXict between an associative disposition to select the smaller reward in order to obtain the large one and the intrinsic features of the food reward, which could be removed by using symbols (Boysen et al 1996;Boysen et al 1999).…”