Figure 1.

Summary of the experimental protocol. (a) A baboon interacting with a touch screen in one of the freely accessible automated work stations. (b) Each trial began with the display of a grid made of 12 white and four red squares (b1). After 400 ms all the red squares became white (b2) and the monkey had to touch the previously red squares (in any order). Squares became black when touched and would not respond to being touched again (b3), forcing individuals to touch four different squares to complete the trial. (c) During transmission trials, the target patterns that the monkeys attempted to reproduce came from the response of the previous individual in the chain (except for the first individual, for whom the target patterns were randomly generated grids). The monkeys had the opportunity to perform random trials both before and after performing the transmission trials. The order of the monkeys was randomized for each of the six independent chains and the order of the 50 trials was randomized at each transmission step (see §2 for further details).