Sensation (redirected from psychologic effects of sensation)

sensation

Mental process (such as seeing, hearing, or smelling) due to immediate bodily stimulation, usually as distinguished from perception. When a stimulus impinges on a sense organ and the organism responds, it is said that the stimulus has been sensed. See also psychophysics, sense-data.

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Sensation

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