The sensory hand

Extract

We explore the world around us with our eyes and hands but, as pointed out by John Napier in Hands (1980), only one of these permits us to see around corners and in the dark. The exploratory capacity of the hand brings to the tactile sense a quality that transcends all the other senses and led Bichat in the early days of the 19th century to refer to touch as the only active sense. An inert hand receives an impoverished sensory input and is but a poor transmitter of information about an object placed in it to the centres for perception. But to observe a skilled Braille reader translating series of raised dot patterns into meaningful language at a rate of up to 100 words per min is to recognize not only the high resolution sensory capacities of the active human hand but also the capacity of the neural signals generated by the mechanoreceptors in the moving fingers to gain rapid access to the highest cognitive centres. This is on the input side. On the output side, apart from the chimpanzees who exhibit a limited capacity, humans are the only species that can communicate meaningfully with the hands. It is not without significance that in naming the individual fingers, medieval anatomists dubbed the middle finger impudicus or obscenus. (medieval lawyers, too, but that is another story).