Do animals understand invisible displacement? A critical review.

The ability to mentally represent the movement of hidden objects (i.e., invisible displacement) is of theoretical importance due to its generally accepted status as an indicator of the development of a powerful type of representational capacity in human children. Over the past few decades, the understanding of invisible displacement has been claimed for a variety of animal species as well. However, a careful review of these studies finds that: (a) many were not properly blinded, (b) many did not properly control for lower-level associative strategies, and (c) success on simplified versions of the tasks can be explained by a simple attentional mechanism rather than by conceptual understanding. Indeed, when lower-level factors are controlled, evidence of understanding invisible displacement remains only for great apes.