Subjects were seated with their hand and forearm firmly strapped in a splint using padded Velcro bands. The splint was attached to a light-weight frame over a horizontal glass surface. A system of air jets lifted the frame supporting the arm 1 mm above the glass surface, eliminating friction during hand movements. Subjects rested their forehead above the work surface, with their hand and arm hidden from view by a mirror. Targets (green selleck inhibitor circles) and hand position (indicated, when specified by the task, by a small round cursor) were projected onto the plane of the hand and forearm using a mirror. The arrangement
of the mirror, halfway between the hand’s workspace and the image formed by the projector, made the virtual images of cursor and targets appear in the same plane as the hand. The workspace was calibrated so that the image of the cursor indicating hand position fell exactly on the unseen tip of the middle finger’s location (i.e., veridical display) (Mazzoni et al., 2007). Hand position was recorded using a pair of
6 degree of freedom magnetic sensors (Flock of Birds, Ascension Technologies, Burlington, VT) placed on the arm and forearm, which transmitted hand position and arm configuration data to the computer at 120 Hz. Custom software recorded hand and arm position in real time INCB024360 datasheet and displayed hand position as a cursor on the computer screen. The same software also controlled the display of visual targets. A total of 60 healthy, right-handed subjects participated in the study (mean age = 24.7 ± 4.9, 25 males). All subjects were naive to the purpose of the study and gave informed consent in compliance to guidelines set forth by the Columbia University Medical Center Institutional Review Board. They were randomly assigned to groups in each experiment. Subjects were asked to make fast, straight, and planar movements through a small circular target displayed veridically using a mirror
and monitor (Huang and Shadmehr, 2009 and Huang until et al., 2008). At the start of a trial, subjects were asked to move the cursor to a starting circle (2.5 mm radius) situated directly in front of them. Once the cursor was in the starting circle, a green, circular target (2.5 mm radius) appeared 6 cm away from the starting circle and the computer played a short, random-pitch tone, prompting subjects to move. If applicable for the trial, a rotation centered at the starting circle was imposed on the cursor feedback. As soon as the cursor was 6 cm away from the starting circle, a small white dot appeared at the cursor position at that time and remained there for the rest of the trial. Thus, the position of the white dot indicated the angular error the subject made in that trial. Subjects were then asked to return the overshot cursor to the target. The cursor disappeared briefly at this point.