Tests of planning and the Bischof-Kohler hypothesis in rhesus monkeys (Macaca mulatta)

The Bischof-Kohler hypothesis posits that nonhuman animals cannot plan for future motivational states that differ from a current state. [Naqshbandi, M., Roberts, W.A., 2006. Anticipation of future events in squirrel monkeys Samiri scireus and rats Rattus norvegicus: tests of the Bischof-Kohler hypothesis. J. Comp. Psychol. 120, 345-357] found that two squirrel monkeys that were not thirsty at the time of choice reversed their preference for a larger amount of food when choice of a smaller amount alleviated future thirst. This apparent anticipation of future thirst contradicts the Bischof-Kohler hypothesis. We used the methods described by Naqshbandi and Roberts with rhesus monkey subjects and found that the monkeys did not alter their behavior in anticipation of future thirst. To assess which factors enhance and inhibit the ability to express planning, we then systematically modified the experimental design in four subsequent experiments and found that monkeys that were not thirsty acted to alleviate future thirst only when the delay between their behavior and the contingent outcome was brief Taken together these results suggest that the inability of rhesus monkeys to display planning resulted from their inability to learn behavior-outcome associations across long-delay intervals as would be expected from traditional accounts of operant learning, rather than from failure to anticipate future motivational states as posited by the Bischof-Kohler hypothesis. (C) 2008 Elsevier B.V. All rights reserved.