Figure 3: Results of experiment 2.

(a) In the test conditions, chimpanzees in the GO group (blue) and NO-GO group (green) released the peg at low rates across the three sessions of four trials. (b) Release rates for actors in the GO group were at ceiling in the pre-test (probe 1) and post-test (probe 2) knowledge probes, whereas NO-GO group actors never released the peg (mean±s.e.m.). Release rates—for both groups—were very low in both the test and social control.