ABSTRACT
For successful manipulation using the precision grip, the motor commands have to be precisely tuned to the relevant physical properties of the manipulated objects. This appears to primarily take place on the basis of previous manipulative experiences with the current object or similar objects, that is, the relevant information related to various objects we have experienced are internally represented in sensorimotor memories. If an erroneous internal model results in inappropriate motor programming, somatosensory signals may automatically trigger compensatory actions and update relevant parameters of the internal model. Tactile afferent innervation, which conveys information about mechanical events particularly at the interface between the hand and the manipulated object, plays a crucial role in this context. This chapter specifically addresses (a) how tactile afferent units innervating the skin of the fingers actually respond during manipulative movements, and (b) the significance of those responses for the control of the manipulation. These questions are considered in relation to a fairly simple but fundamental manipulative task: to lift, hold in the air, and replace a small test object using the precision grip formed between the tips of the thumb and an opposing finger. It is shown how tactile afferent signals may be utilized in the adaptation of the motor commands to the weight of the object and its frictional characteristics in relation to the skin.
