Fig. 1.

Behavioral tasks. A: an example schematizing the continuous tracking task. The subject’s hand (dashed line) follows a “tracked target” (white circle with a red border), which moves around the screen at 6 cm/s. In the actual display, only the circle and a cross indicating hand position are visible. When the tracked target is at point 2, a “choice target” appears (circle 3), offering a potential new movement (gray dotted arrow), but the subject ignores it and continues to track the current target. At point 4, a new choice target appears (circle 5) and the subject switches to it, so it now becomes the new tracked target. Individual “trials” are defined by the colored segments, each of which presents the subject with a single decision scenario, and dotted gray lines indicate the options not taken. B: three variations of the continuous tracking task. In the “distance block,” the choice target always appears in a direction orthogonal to the current tracking direction, but at 5 different distances (only 3 shown). In the “angle block,” the target always appears at a distance of 4.8 cm, but at 1 of 5 angles with respect to the current tracking direction. In the “size block,” the tracked target is gradually shrinking and the choice target always appears orthogonal to the current tracking direction and at a distance of 4.8 cm, but can be either larger or smaller than the currently tracked target. C: the discontinuous tracking task. The tracked target (red circle) jumps by 4.8 cm every 900 ms, and the subject tracks it with point-to-point movements. At time 1, the next target (2) is displayed along with 2 gray circles (3 and X), foreshadowing future targets. These turn red (not shown) 900 ms after the subject moves into target 2. Now the subject can make a choice and, in this example, chooses to go to target 3, which is “aligned” with the previous point-to-point movement. At time 5, the subject chooses to go to target 6, which is “unaligned” with the previous point-to-point movement. D: the replay task. The task is broken into individual trials, each starting when the subject places the cursor in the red circle, at which time 2 cues appear (gray circles). After 900 ms they turn red, indicating the GO signal, when the subject can freely choose either target. Importantly, the placement of the start and target circles is a replay of choice scenarios previously experienced when performing the discontinuous tracking task (in this example, from time 2 in C).