ABSTRACT
In the literature, successful achievment of stage 6 object-concept has been reported not only for apes but also for a variety of lower primate species. The target object is surreptitiously dropped off under or behind the last screen passed, and the experimenter exposes the empty container and allows the subject to act. Searching for the target object under or behind the correct screen is scored as a successful response. A more convincing demonstration of the mental recreation of the invisible displacements of the object would be children’s ability to reproduce the path of the hider’s hand, a phenomenon that Corrigan, Uzgiris and Hunt, and others have called “systematic search.” Only the gorilla follows a systematic search pattern that consistently traces back the invisible displacements of the target object in quite a variety of different situations and, furthermore, its performance is not disrupted by the successive modifications introduced into the task.
