Everything's in the task.
The standard task for studying voluntary motor control is the "center-out task," in which a monkey or other subject must move its hand from a central location to targets placed on a circle surrounding the starting position.
To plan the movement, says Daniel Moran, PhD, associate professor of biomedical engineering in the School of Engineering & Applied Science and of neurobiology in the School of Medicine at Washington University in St. Louis, the monkey needs three pieces of information: current hand and target position and the velocity vector that the hand will follow.
A variation of the center-out task with multiple starting positions allows the neural coding for position to be separated from the neural coding for velocity.
By themselves, however, the straight-path, unimpeded reaches in this task don't let the neural coding for velocity to be distinguished from the neural coding for target position, because these two parameters are always correlated. The initial velocity of the hand and the target are always in the same direction.
To solve this problem and isolate target position from movement direction, doctoral student Thomas Pearce designed a novel obstacle-avoidance task to be done in addition to the center-out task.
Crucially, in one-third of the obstacle-avoidance trials, either no obstacle appeared or the obstacle didn't block the monkey's path. In either case, the monkey could move directly to the target once he got the "go" cue.