Fig. 2.

Active interest of chimpanzees across the movement conditions. The imitated subjects displayed active interest for significantly longer than the other subjects (two-tailed Mann–Whitney U test: U = 7.5, N = 7+6 subjects, p = 0.036). The imitated subjects also showed active interest for longer when imitated by the robot than when the robot imitated the assistant (Wilcoxon’s matched-pairs signed-ranks with Hommel–Hochberg corrections: z = −2.21, N = 7 subjects, p = 0.027). Total number of subjects is shown in brackets