Figure 1.

Stimuli sets (a) gorillas’ stimuli set; (b) Migwan’s summer set; (c) Migwan’s fall set. For each set, the three stimuli on the left are the training stimuli used to create the NA and PA sets (N, P, and A) while the two stimuli on the right are the novel stimuli introduced during probe trials. On each trial, the subject would see only two stimuli displayed next to each other on the screen according to which stimuli were designated as A, P and N for that subject.