the ability of animals and man to sense environmental factors by means of receptors in the skin; in the locomotor system, which includes the muscles, tendons, and joints; and in some mucous membranes, such as those on the lips and tongue.
The tactile process is based on stimulation of various types of receptors: mechanoreceptors that perceive contact, pressure, and tension; thermoreceptors that perceive heat and cold; and pain receptors. This information then reaches and is transformed by the central nervous system, including the cerebral cortex. The sensation of touch can be quite varied because it results from a complex perception of different properties of a stimulus acting on the skin and subcutaneous tissues. The perception of environmental objects by touch permits evaluations to be made concerning their shape, size, surface properties, consistency, temperature, dryness or wetness, and position and movement in space. At the cellular level, touch breaks down into several different receptor processes: there is no single morphological type of tactile cell.
The sense of touch greatly broadens the organism’s impressions of its surroundings and plays an important role in its vital activity. In many lower animals the sense of touch, together with chemical sensitivity, is the principal means of perceiving the environment. To some extent, touch substitutes for the sensory organs of sight and hearing when they are injured. Touch permits blind persons to read, perform a variety of delicate manual operations, and orient themselves in space. In persons who are both blind and deaf, touch is the main source of information about the outside world and can be developed to an exceptionally high degree. The term “touch” is becoming less common because of increasing knowledge of the receptor processes’ cellular mechanisms; the mechanisms of mechanoreception, thermoreception, and pain are usually considered independently.
O. B. IL’INSKII
a performer’s particular manner of producing sound on the piano through various ways of pressing and striking the keys. Each pianist has his own individual touch, which depends on his physiology and artistic intent. J. Field and S. Thalberg produced a soft, “velvety” tone; S. V. Rachmaninoff and A. G. Rubinstein played with a deep, rich tone; and K. N. Igumnov elicited a tender, lyric sound.