What is the evidence for an equivalence between objects and pictures in birds and nonhuman primates?

Abstract This paper examines the way birds and nonhuman primates process pictures of objects. After having defined three main modes of picture perception that might occur in animals (independence, confusion, and equivalence), we review the literature providing direct evidence in favor of these three possible modes of processing. This review reveals that experimental evidence for object/picture equivalence is weak and often inconsistent in birds, and even in nonhuman primates. It also underlines the role of several experimental factors in picture processing modes.