Figure 4

An example trial in the final testing stage. (a) At the beginning of each trial, a starting key appeared in the bottom center of the screen. (b) After chimpanzees touched the starting key, an image of a chimpanzee body with all body parts at a slight distance from each other appeared in one location on the screen. (c) The same picture with the targeted body parts highlighted in a yellow hue quickly took turns to appear with the image in (b), create a flashing visual effect for three rounds. (d) Chimpanzees were trained to touch the flashing part, and the other parts subsequently turned gray. (e) At the same time, another image of a chimpanzee body appeared in another location on the screen. Here, a different chimpanzee picture is used as an example, although the second pictures were sometimes the same as the first. (f) Chimpanzees touched one part of the second picture, and the other body parts turned gray. This example depicts them touching the arm area. This screen remained visible for a short period of time before all images disappeared and the starting key appeared again for the next trial.