Spatial rotations and transpositions in orangutans ( Pongo pygmaeus) and chimpanzees ( Pan troglodytes).

This study investigated the ability of three chimpanzees and three orangutans to track the position of a reward after a series of displacements. The reward was placed under one of two opaque containers resting on a platform. Experiment 1 investigated rotational displacements in which the platform was rotated 0 degrees, 180 degrees, or 360 degrees. Experiment 2 investigated transpositional displacements in which the platform remained stationary while the containers either remained stationary, or swapped their positions (in a one- two- or three-step sequence). In both experiments, the initial position of the reward was indicated either by directly showing the reward under the containers, or by placing a landmark, which had been previously associated with the reward, on top of the baited container. Subjects successfully tracked the reward through rotations and transpositions when they had seen it, but their performance substantially deteriorated when the landmark indicated the reward's initial position, even though subjects successfully used the landmark to find the reward in the absence of displacements. This decrease was especially pronounced in rotational displacements. A language-trained orangutan outperformed all the other apes and solved all problems.