Perception and Action interactions (New)
The influence of experience on visually- and haptically-guided grasping.
Because the visuomotor system must update information, moment to moment, as the body and the visual world moves, it has been considered to operate ?online,? and its computations are performed without conscious awareness. Some studies however, have shown that reach-to-grasp movements are susceptible to the influence of practice or experience. In one study we showed that awkward grasps (grasps made using the thumb and ring finger) are initially sensitive to a visual illusion. One hour of practice with the awkward grasp for three consecutive days reduced the effect of the illusion on the grasp to an extent where it resembled the more common pincer grasp (i.e. thumb and index finger). Cavina-Pratesi et al. explored the effects of long-term training on grasp kinematics by using professional magicians with years of experience and asking them to either pick up or pretend to pick up an object. In control participants the two types of grasped differed considerably in their kinematics, but they were strikingly similar in the group of magicians. The authors concluded that prolonged practice may enable the visuomotor system to calibrate actions based on visual inputs displaced from the action. We have begun to investigate the effects of short-term practice on visually- and haptically-guided grasping. The proposed project will specifically address the following question: Can a short grasping experience modify body size representation? Recently it has been shown that although we are very accurate in estimating the length of our own body this representation is remarkably plastic. The perception of the length of our arm is significantly greater after 15 minutes of practice with a tool (i.e. rake) that extends the arm?s capability for reaching. We will investigate if this remarkable experience-dependent plasticity of body representation extends to the hand and whether it occurs without the use of a tool. Estimates of hand size will be recorded before and after participants continuously grasp objects for 15 minutes. Objects (spheres) will be either, large, affording a full extension of the hand, or small, affording a pincer grasp. If this experience can modify body representation then we expect participants? perceptions of their hands to be larger after they had practiced with the large objects and the opposite for the small objects.
