sensation(redirected from Sensation disorders)
Also found in: Dictionary, Thesaurus, Medical, Legal.
A term commonly used to refer to the subjective experience resulting from stimulation of a sense organ, for instance, a sensation of warm, sour, or green. As a general scientific category, the study of sensation is the study of the operation of the senses. Sense receptors are the means by which information presented as one form of energy, for example, light, is converted to information in the form used by the nervous system, that is, impulses traveling along nerve fibers. See Sense organ
Each sense has mechanisms and characteristics peculiar to itself, but all display the phenomena of absolute threshold, differential threshold, and adaptation. Not until sufficient stimulation impinges on a receptor can the presence of a stimulus be detected. The quantity of stimulation required is known as the absolute threshold. Not until a sufficient change occurs in some aspect of a stimulus can the change be detected. The magnitude of the change required is called the differential threshold. Under steady stimulation there is a decrease in sensitivity of the corresponding sense, as indicated by a shift in the absolute threshold and in the magnitude of sensation. After the stimulation ceases, sensitivity increases. An obvious example of visual adaptation occurs when one goes from bright to dim surroundings or vice versa.
With fairly good accuracy humans can localize visual objects, sounds, and cutaneous contacts and can discriminate the spatial orientation of the body and its members. With rather poor accuracy humans can localize many of the stimuli originating within the body.
With the exception of hearing, in which sense localization depends on differences in the acoustic stimuli reaching the two ears, there appears to be a common principle involved in giving spatially separated receptors their different local signs. Stimulation at different points on the receptive surface results in peaks of electrical activity at different loci in the brain. In no sense is there anything like a private wire from each sensory cell to a corresponding point in the brain. In fact, there are so many opportunities for a signal to go astray on its way from the receptor to the brain that it is surprising that spatial discrimination is as good as it is. Nevertheless, there is clear evidence that, by a combination of anatomical and functional arrangements, spatial differences at the receptor level are translated into topologically similar spatial differences in brain activity. See Hearing (human)
The nerve fibers between receptor and brain do not serve merely as transmitters of sensory information. Their interconnections enable them to influence one another's sensitivity and to perform logical operations like those carried out inside computers. As a result the information arriving in the sensory areas of the brain is not merely a more or less faithful replica of that presented to the receptors but in addition has had certain aspects of the information selected for special signaling. See Chemical senses, Somesthesis, Taste, Vision
the reflection of the properties of things in the objective world, resulting when things act upon the sense organs and arouse the nerve centers of the cerebral cortex. Sensation is the starting point of cognition and an inseparable part of it. Pointing to the reflection of quality as the chief element in sensation, V. I. Lenin wrote that “the very first and most familiar to us is sensation, and in it there is inevitably also quality” (Poln. sobr. soch, 5th ed., vol. 29, p. 301). There are many kinds of sensations, including tactile, visual, aural, vibrational, and olfactory; there are also sensations of the muscles and joints as well as sensations of temperature, taste, pain, equilibrium, and acceleration. The special feature of each sensation is called its modality. Sensations of different modalities are not comparable with one another.
In the course of evolution, sensation arises on the basis of irritability associated with the development of a nervous system. However, specific sense organs have been developed only for a few types of energy. Many other properties of the objective world, such as form, size, and distance of objects from one another and from the observer, are sensed only when various sense organs interact.
A leading role in man’s sensory knowledge of reality is played by visual sensations, which are closely linked to tactile sensations. “Touch and sight supplement each other to such an extent that from the appearance of an object we can often enough predict its tactile properties” (F. Engels, in K. Marx and F. Engels, Soch., 2nd ed., vol. 20, p. 548). Tactile sensations include dermotactile sensations, sensations of the muscles and joints, and those of temperature and pain. Dermotactile sensations reflect touch, pressure, and the surface qualities of an object, such as smoothness, roughness, size, hardness, elasticity, and impermeability.
Vibrational sensations reflect periodic changes of pressure linked to mechanical oscillations of moving bodies in the environment; these sensations are especially keen in the blind. Hearing represents a complex of heterogeneous sensations, including pitch, volume, and timbre. The development of human hearing is most closely linked with the development of auditory language as the most important means of communication and with the development of music. The chemoreceptors of smell and taste are also important to sensation.
A characteristic of sensation is the localization of the object of sensation. In sensing color, for example, a person attributes it to a specific surface of an illuminated body occupying a specific place in space; sensing a sound, a person localizes the source of this sound.
In contrast to the sensations of animals, human sensations are mediated by man’s object-oriented practical activity and the whole process of the sociohistorical development of culture. In the words of Marx, “the human eye enjoys things in a way differently from the crude, nonhuman eye; the human ear differently from the crude, nonhuman ear, etc.” (K. Marx and F. Engels, Iz rannikh proizvedenii, 1956, p. 592). In principle, human sensations are of an intelligent and conscious nature, although unconscious sensations also exist.
The variety of sensations reflects the qualitative variety of the world. Lenin’s theory of reflection regards sensation as a copy or photograph of reality, a subjective image of the properties of the objective world. His theory stands in contrast to the views of the adherents of physiological idealism, who assert that sensations are only conventional signs or hieroglyphs for the properties of objects. It is also opposed to the mechanistic distinction between primary and secondary qualities, which leads to agnosticism, subjective idealism, and the view that things are complexes of sensations. In criticizing the adherents of Machism, Lenin emphasized that sensations give us more or less faithful images of the objective properties of things, although different sensations possess various degrees of adequacy in reproducing these properties.
A source of man’s knowledge about the surrounding world, sensation is an element in the integral process of human cognition, a process that also includes perceptions, images, and concepts.
REFERENCESLenin, V. I. “Materializm i empiriokrititsizm.” Poln. sobr. soch, 5th ed., vol. 18.
Mach, E. Analiz oshchushchenii i otnoshenie fizicheskogo k psikhicheskomu, 2nd ed. Moscow, 1908. (Translated from German.)
Anan’ev, B. G. Teoriia oshchushchenii. Leningrad, 1961.
Boring, E. G. Sensation and Perception in the History of Experimental Psychology. New York-London .
Piéron, H. La Sensation. Paris, 1953.
A. G. SPIRKIN