Stimulus

views updated

Stimulus


A stimulus (plural, stimuli) is any event that triggers a response in an organism. When an organism reacts, or changes, its behavior because of some environmental change, it is responding to a stimulus. An ability to respond to what is going on around them is one of the characteristics of living things.

In order to survive in a world full of constant change, activity, and motion, organisms have developed a wide range of receptors that react to particular types of stimuli. If organisms are not immediately aware of changes in their environment, they may not be able to adapt. Therefore, an organism must be able to detect change and to adjust itself. The organism must respond to change in an appropriate way, or it will not live long. Vertebrates (animals with a backbone) have developed elaborate and sensitive nervous systems that enable them to know what is going on about them. This system enables them to react quickly to each new situation.

Vertebrates have five main senses. Each have specialized receptors that respond to certain types of stimuli. A person's eyes have receptors that detect light, while ears detect sound; the skin detects pressure and temperature; the tongue detects dissolved chemicals; and the nose detects airborne chemicals. Although each type of receptor reacts to only one particular type of stimulus, they all work on the same principle. A sense receptor is activated by a certain type of energy change. Therefore, when a certain energy change, or stimulus, occurs in the external environment, the appropriate cell, or nerve ending, reacts and converts this into a nerve impulse. The nerve impulse is carried to the brain by sensory neurons. The brain decodes the signal and tells a person what he or she is sensing. It also transmits any necessary signals to the muscles or glands (organs in the body that produce a special substance like hormones or enzymes) to carry out a particular action.

Organisms also have rapid or immediate responses to certain stimuli that are built into their nervous systems. These are called reflex actions and are usually geared to matters of well-being and survival. As a result, a person will instantly pull his or her hand away from a hot stove without thinking. The heat sensed by the person's skin is the stimulus and the hand jerking back is the response. Such an instantaneous reaction is called an unconditioned response because it occurs with no learning or experience involved. The idea of stimulus is closely associated with that of life or living, since all organisms, from the simplest to the most complex, are geared to receive and react to stimuli.

[See alsoBrain; Hearing; Integumentary System; Sight; Smell; Taste ]

Stimulus

views updated

Stimulus

Resources

The term stimulus has many meanings; very generally, it is any occurrence (be it an external event, or anything perceived or thought) that causes a detectable response. Stimulus is often used with qualifying terms to further specify its meaning, for example, conditioned stimulus and neutral stimulus.

Various fields of study use the term stimulus in different ways. In psychology, it is most often used to describe energy forms that reach sense organs and cause a response. For example, the visual sense using the eyes responds to photic radiation or light. Because human sense organs respond to a limited number of energy forms, and even then to only limited amounts of that energy, some energy reaching the sense organs is not detected and does not cause a response. The energy reaching the sense organs but not causing a response may be deemed a stimulus to a physiologist, but for psychologists it would not be considered a stimulus unless it had been responded to or detected by the organism. A stimulus may also be an internal mental evnt that causes a response.

Stimulus is the primary term in stimulusresponse theory, which refers to a number of learning theories that are theoretically based on conditioned bonds or associations between a stimulus and response. The associative bonds are formed through the repeated pairing of certain stimuli and certain responses. Most of these theories are also behavioristic in that they focus on behaviors and do not look at mental processes, and they see the environment as the most important determinant of human behavior. Indeed, these theories view the bond between stimulus and response as the basis of behavior and believe that psychologys primary goal should be to discover rules governing how stimuli and responses interact. The two dominant stimulusresponse theories are classical and operant conditioning theories.

See also Perception.

Resources

BOOKS

Friedrich, M.J. A Bit of Culture for Children: Probiotics May Improve Health and Fight Disease. Journal of the American Medical Association. No. 284 (September 2000): 13651366.

Stimulus

views updated

Stimulus

The term stimulus has many meanings; very generally, it is any occurrence (be it an external event, or anything perceived or thought) that causes a detectable response. Stimulus is often used with qualifying terms to further specify its meaning, for example, conditioned stimulus and neutral stimulus.

Various fields of study use the term stimulus in different ways. In psychology , it is most often used to describe energy forms that reach sense organs and cause a response. For example, the visual sense using the eyes responds to photic radiation or light . Because human sense organs respond to a limited number of energy forms, and even then to only limited amounts of that energy, some energy reaching the sense organs is not detected and does not cause a response. The energy reaching the sense organs but not causing a response may be deemed a stimulus to a physiologist, but for psychologists it would not be considered a stimulus unless it had been responded to or detected by the organism . A stimulus may also be an internal mental event that causes a response.

Stimulus is the primary term in stimulus-response theory, which refers to a number of learning theories that are theoretically based on conditioned bonds or associations between a stimulus and response. The associative bonds are formed through the repeated pairing of certain stimuli and certain responses. Most of these theories are also behavioristic in that they focus on behaviors and do not look at mental processes, and they see the environment as the most important determinant of human behavior . Indeed, these theories view the bond between stimulus and response as the basis of behavior and believe that psychology's primary goal should be to discover rules governing how stimuli and responses interact. The two dominant stimulus-response theories are classical and operant conditioning theories.

See also Perception.

Resources

books

Atkinson, R.L., R.C. Atkinson, E.E. Smith, and D.J. Bem. Introduction to Psychology. 10th ed. New York: Harcourt Brace Jovanovich, 1990.

Masin, S.C., ed. Foundations of Perceptual Theory. New York: Elvesier Science, 1993.

periodicals

Friedrich, M.J. "A Bit of Culture for Children: Probiotics May Improve Health and Fight Disease." Journal of the American Medical Association no. 284 (September 2000): 1365-1366.

stimulus

views updated

stim·u·lus / ˈstimyələs/ • n. (pl. -li / -ˌlī/ ) a thing or event that evokes a specific functional reaction in an organ or tissue: areas of the brain which respond to auditory stimuli. ∎  a thing that rouses activity or energy in someone or something; a spur or incentive: if the tax were abolished, it would act as a stimulus to exports. ∎  an interesting and exciting quality: she loved the stimulus of the job.ORIGIN: late 17th cent.: from Latin, ‘goad, spur, incentive.’

stimulus

views updated

stimulus Any change in the external or internal environment of an organism that provokes a physiological or behavioural response in the organism. In an animal specific receptors are sensitive to stimuli.

stimulus

views updated

stimulus (stim-yoo-lŭs) n. (pl. stimuli) any agent that provokes a response, or particular form of activity, in a cell, tissue, or other structure.