Linking cognitive and reaching trajectories via intermittent movement control (Q2437261)

In a classical psychophysics experiment, subjects have to touch a specific part of a screen (e.g. a spot, either on the left or on the right) according to some stimulus outcome. For instance, they may have to touch the side of the screen displaying a red square, or whatever side corresponding to a dot shifting. If they are instructed to do so as fast as possible, the classical interpretation of their arm movement while reaching the spot is simple: The brain first gathers evidence about the stimulus, reaches a decision when a bound is attained, and then programs the arm movement. The time between the stimulus onset and the beginning of the movement reflects those two processes: building a decision and a motor plan. More recent accounts of arm movements noticed that the trajectory is usually not straight, but rather curved. They thus hypothesized that once a first decision is made in the perceptual and motor brain, the movement is continuously monitored. Moreover, the subject can eventually ``change his mind'', switching to another decision, leading to curve the initial movement. This paper suggests and experimentally tests a novel view, which differs from this approach in three ways. First, it assumes that the movement might begin before a decision is reached, based on partial information processing. Second, it assumes that the motor control is not continuous, but intermittent. Last, unlike other models, it posits that the initial movement, although it might begin before a decision is made (i.e. the subject doesn't still ``know'' if he should spot the left or right side of the screen), does take into account partial information. Thus, the aim of the submovement is not, as it was once believed, the center of the screen, but a point somewhere between left and right, depending on the available evidence so far. The authors give experimental arguments in favor of this model and discuss possible use of it in the future. Mainly, their account could lead to a finer description and understanding of decisional and perceptual processes.