Figure 2. Proportion of exchanges through the picture frames in the Test Phase.

The proportion of the chimpanzees’ exchanges in which the chimpanzees returned the token through the picture frame in the Test Phase in each of the four conditions (when tested as the subject) in order to obtain the high-value reward (a grape). Also shown are the responses of the chimpanzees in the Different condition when tested in the role of the partner (for which, like subject chimpanzees in the High-value Same condition, they received a high-value grape regardless of whether they exchanged their tokens directly through the mesh, or through the picture frame, Table 1).