Sensory and Motor Functions of the Hand

Abstract

Needless to say, the hand is the principal instrument for writing and writing is one of the most fundamental things we do with the hand. It is therefore worthwhile to consider in some detail the hand in a book dealing with several aspects of writing. In this chapter I do not claim to present a complete and detailed review of the functions of the hand, but I will try to describe some fundamental sensory and motor mechanisms in an attempt to construct an overview of hand functioning. The hand is both a sensory and a motor organ, so that the sensory functions cannot be completely separated from the motor ones. When we explore the world with our hands, the tactile information arriving at our brain plays an essential role in the ongoing motor behavior. This continuous sensory inflow and motor outflow represents what has been called “active touch” (Gibson, 1962) or “haptics” (Revesz, 1950; Kennedy, 1978). Thus these terms mean the combined action of skin, joints and muscles for acquiring information from the external world. On the other hand, the movement of an object across a stationary hand represents the condition we call “passive touch.” In such a situation the hand behaves merely as a sensory organ. In contrast, when the hand performs movements such as preshaping in grasping behavior, it behaves as a motor organ. The hand can therefore be used as a sensory detector, a motor device, or both.