Abstract
In the current investigation, task-irrelevant local features of an object were manipulated during a reach-to-grasp task. Specifically, 3 cm diameter circular discs, were grasped with surface features manipulated from trial-to-trial. Local feature conditions were a) solid white, b) solid black; lines oriented through clock positions: c) 8 and 2; d) 10 and 4; e) 12 and 6, f) 9 and 3.The lines were 1 mm thick and spaced 3 mm apart.The position of the wrist, index finger and thumb were tracked using the OptoTrak (Northern Digital Inc.). Main dependent measures were grip aperture, peak grip aperture, grip orientation; movement kinematics: Peak Acceleration and velocity. The finding most relevant to the current experiment was the sensitivity of grip formation to the presence and angle of the lines. In control conditions (i.e., solid white and black) individuals generally grasped the object at 35° from horizontal. While for conditions where line features were involved, grip angles increased as a function of line condition, to the order of i) 8 and 2: 40°; ii) 12 and 6: 41°; iii) 10 and 4: 45°; iv) 9 and 3: 49°. Therefore, orientations involving a greater angle magnitude from horizontal resulted a greater grasp angle. Overall, the findings suggest that the control of grasping may also be dictated by local features (often formed into global composites). When considered within the canon of dedicated streams for perception and action, this would suggest a dorsal stream that is 'feature tuned' to the local features of the object.Acknowledgments: NSERC, CFI, BCKDF