OBJECT PERMANENCE OF CAPUCHIN MONKEYS - A STUDY OF INVISIBLE DISPLACEMENTS

Object permanence OP is a cognitive capacity whose function is to attribute continued existence to disappearing objects and to localize physical and social objects in space (Etienne, 1984). According to Piaget (1937), OP develops in a six-stage sequence. At the end of that sequence (i.e. Stage 6), the infant is able to mentally represent the movements of an object that is absent from his or her perceptual field; that is to infer movements of the object that have not been perceived. In doing so, the infant master problems with invisible displacement. In a typical invisible displacement, a target object is first hidden in a small movable container (e.g., hand, cup) and both are moved behind another screen. Then the object is dropped from the container and left behind the screen so that the subject cannot perceive the transfer. Finally, the container is moved out from behind the screen and is shown to be empty. The subject must deduce that the object is behind the screen although he/she did not perceive the transfer. Research showed that apes and dogs solve invisible displacements whereas monkeys and cats fail such problems. However, there are contradictory results regarding the capacity of capuchin monkeys to solve object permanence tasks with invisible displacements (ID). Mathieu et al. (1976) and Schino, Spinozzi, and Berlinguer (1990) concluded that capuchin monkeys mastered ID, but Natale and Antinucci (1989) reached an opposite conclusion. Methodological differences may account for this discrepancy. Mathieu et al administered ID with a logical procedure whereas Natale and Antinucci and Schino et al. used a comprehensive procedure. In a logical procedure, the container is shown to be empty or not after each screen visited whereas in the comprehensive procedure it is shown to be empty only after the last screen is visited (the object having been left behind any one of the screens visited). In the present research capuchin monkeys were administered a multiple ID task (Exp. 1, N = 3) and a simple ID task (Experiment 2, N = 2) with both procedures. Results showed that capuchins failed both ID tasks whatever the procedure used. These results suggest that capuchins do not possess mental representation (at least as measured in Piaget's theory) which is in agreement with previous research that reached a similar conclusion regarding tool use in this species. In addition, a detailed analysis of behaviour suggests that the typical Piagetian task appears to be unsuited to the attentional and behavioural characteristics of this species. More specifically, it is argued that in the natural environment invisible displacement involve social objects (i.e., mobile and autonomous organisms) rather than physical objects as in the typical Piagetian task. The discussion emphasizes the need to design more ecologically relevant tasks in order to assess representational capacities in animals.