Comprehension of object permanence and single transposition in gibbons

Abstract

Gibbons have been historically overlooked in the field of comparative social and physical cognition. This study investigated the cognitive abilities of lesser apes in two object permanence tasks. Five gibbons (two Symphalangus syndactylus and three Hyloblates leucogenys) participated in an object permanence task and a single transposition task. The first experiment consisted of a simple visible displacement object permanence task, in which the experimenter placed a food reward under one of three cups placed on a board while the subject observed. The cups were flipped over the food reward and the subject was then asked to gesture towards the correctly baited cup. The second experiment was similar to the first, only a single transposition condition was added. The food reward was placed under one of three cups placed on the same board while the subject observed. The experimenter then switched the cup containing the food reward with one of the two empty cups. The experimenter did not touch the third cup. Once the cups were moved, the subject was asked to gesture towards the correctly baited cup. All gibbons performed significantly above chance in both tasks. There was some variability across subjects in a learning effect and side bias, however, all demonstrated they were capable of identifying an object once unseen and able to track that object once unseen.