Figure 2
The top row illustrates the time course of a trial at the beginning of the session. Movement targets (a blue and a green circle) are first displayed to inform the subject about the accuracy requirement of the arm movement to execute later in the trial. The color of the targets at this stage is not informative of their color at the time of the perceptual decision. The diameter of the targets is 4 cm during the first trial of the session. Decision difficulty options are then displayed. In this example the subject chooses “5”, which corresponds to a difficult (low coherence) perceptual decision to make. The decision circle containing 100 blue and green tokens, and the blue and green movement targets then appear. The dominant color among the tokens determines the correct target to select. The subject reports the decision by moving the handle in the target whose color corresponds to her/his choice. The subject earns the amount of points she/he chose (“5” in this example) if she/he accurately reaches to the correct target. She/he loses the points if she/he accurately reaches the target corresponding to the wrong decision. After the first trial, the size of the movement targets evolves from trial to trial, being linearly and inversely indexed to the number of points accumulated during the session. As a consequence, at the end of the session (bottom row), when the subject gets close to 200 points, the target size is small (diameter close to 1 cm) and the required motor accuracy is high. As illustrated in this example, an integrated control of resources between decision and action predicts that subjects would choose in this situation an easy decision (“1”) more frequently than at the beginning of the session, when the required motor control was low. Known to the subjects at the start of the experiment, no point is deducted in case of failing to reach or stop in the chosen target (whether correct or not).
