Experimental paradigm designed to naturally evoke the learning of obstacle-avoidance. (A) Temporal epochs and visual stimuli in each single trial of the experiment. The monkeys were neither conditioned to end the reach at a particular time nor to reach a particular velocity peak. They moved at their own natural pace. (B) Block-design experiment to naturally evoke learning consisted of straight reaches, followed by new reaches around physical obstacles for which the monkeys had not been trained, and then straight reaches again. Red circle marks the site of maximal memory response in the visual field from a posterior parietal neuron used to guide the initial placement of the obstacle. The second placement was on the opposite side of the board.