Numerical ordering in a chimpanzee (Pan troglodytes): Planning, executing,and monitoring

Perceptual and cognitive processes underlying the skill of ordering numeral s were assessed in a female chimpanzee (Pan troglodytes) with previous expe rience in computer-assisted numerical competence tasks. The subject was req uired to order 3 numerals from the range of 0-9 into an ascending series, w ith occasional probe trials (referred to as switch trials) in which the pos itions of the 2nd and 3rd numerals were exchanged immediately after the sel ection of the 1st. On these trials, errors were scored frequently, whereas correct responses to the intermediate numeral became reliably slower. These and other data indicated that the subject had already established, before making the 1st choice, (a) the correct sequence in which she was to select the numerals and (b) the motor sequence leading to a,correct answer. These findings show that a 3-unit ordering task is supported in the chimpanzee, m uch as it is in humans, by planning, executing, and monitoring phases.