RESUMEN
The effects of visual information about object size on grip force programming were investigated. Fifteen subjects (26.1±7.6 yrs) repeated lifts of a cube-like grip apparatus (30×30×30 mm, 30g) using a thumb and index finger, while three boxes of different sizes but equal weight (small : 10×10×60 mm, medium : 30×30×60 mm, large : 60×60×60 mm, 25g) were pseudorandomly presented by attaching beneath the grip apparatus. Lifting tasks were performed in two visual conditions. In the full-vision condition, subjects could perceive the box size prior to the lift-off of the grip apparatus, similar to normal everyday conditions. In the obstructed-vision condition, subjects could not perceive the box size due to the placement of a screen during the initial lifting phase, and only the grip apparatus were visible over the screen. The grip apparatus measured grip and load forces during the trial and we found that the grip and load force applied to the grip apparatus in the full-vision condition significantly increased with box size regardless of equal weight. In contrast, when the size information was removed in the obstructed-vision condition, the force applied for a given box of any size was always that adequate for the largest box, suggesting that the scaling of fingertip force by utilizing size information may be achieved by reducing forces for the smaller boxes on the basis of the force output applied for the largest box, but not by increasing forces on the basis of the force output applied for the smallest box.