Figure 1: Setup for memory studies.

(a) In Study 1 (Long Delay), apes first learned that one location was consistently baited with food in initial learning trials, and then were tested on their memory for that location in test trials after a one-week delay. Experimenter 1 (E1) baited the locations, and Experimenter 2 (E2) centered the ape at the starting position on each trial. (b) In Study 2 (Multiple Locations), apes observed an experimenter hide four test pieces of food in a large enclosure; four control pieces were hidden at matched locations. Apes could then search in the enclosure following a 10-min delay. Study 3 (Motivational Control) had a similar setup, but the food pieces were placed directly on the ground, thus removing the memory demands associated with the task while still requiring motivation to search for the food.