sensation

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For more information on sensation, visit Britannica.com.

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 also 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 also 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 also Chemical senses; Pain; Somesthesis; Vision.

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A sensation is a subjective experience resulting from the stimulation of a sensory receptor (a specialized nerve cell that is excited by some physical or chemical stimulus). Sensations are presumed to arise as a result of nerve activity in certain areas of the cerebral cortex, which receive incoming signals from the sensory receptors.

Aristotle recognized only five senses — vision, hearing, taste, smell and touch, each associated with a particular sense organ (counting the skin as a sense organ). The term ‘special sense’ is still used for vision, hearing, taste and smell. In reality, there are many more sensory systems, including those that mediate the sensations of pain and temperature, those of the positions of parts of the body (proprioception), and those related to balance (conveyed by the vestibular apparatus). A more fundamental way of classifying sensory receptors is according to the types of physical stimuli to which they respond. It is remarkable that all the majesty of our sensory experiences depends only on sensitivity to light, and to mechanical, chemical, and thermal stimulation.

The experience of our own bodies, somatic sensation (from the Greek ‘soma’ meaning body), conventionally includes sensations arising from nerve endings in skin, muscle, bones, and joints. A different term, visceral sensation, is used to describe awareness (usually discomfort) arising from receptors in the internal organs (viscera). Such sensations are only vaguely localized compared to somatic sensations, and in some instances may be ‘referred’, that is, felt to be coming from a site quite different from where the excitation arises. For instance, the pain of angina, originating from sensory fibres in the muscle of the heart, is typically felt in the left shoulder and upper arm. Some visceral sensations, such as the feeling of a full bladder, are associated with normal functions; others signal abnormality, such as the pain of intestinal colic or a growing tumour.

Sensory experiences have distinct subjective qualities, such as colour, pitch, tickle, bitterness, and floral. These are sometimes referred to as ‘modalities’ or ‘sub-modalities’ of sensation, especially for sensations derived from the skin. Valiant, partially successful, attempts have been made to correlate each such mental property with a particular specialized type of sensory receptor, nerve pathway or region of the brain. In 1823, the British neurologist and anatomist, Sir Charles Bell, first described evidence for what subsequently became known as Müller's Law of ‘Specific Nerve Energies’ (after the German physiologist, Johannes Müller). Bell wrote: ‘every nerve of sense is limited in its experience, and can minister to certain perceptions only’. He and Müller cited examples of false sensations, elicited by inappropriate stimulation of particular nerves. For instance, pressing on the side of the eyeball with a finger, which causes direct, mechanical stimulation of the retina, gives rise to a ‘phosphene’ — a visual sensation in the form of a curious blob in the part of the visual field corresponding to that region of the retina. Certainly, many modalities of sensation can be identified with particular specialization of the sensory receptors involved. Touch, vibration, warmth, and coldness are indubitably associated with particular, highly specialized nerve endings in the skin.

Sensory receptors provide information about the quality of the stimuli that they detect, giving rise to what philosophers call the qualia of conscious perceptual experience. We see colour and brightness, hear pitch and timbre, and taste sweetness and sourness: we can distinguish whether an object touching the skin is sharp or smooth, hot or cold. But stimulus quality is not the only kind of information that sense organs provide. They also transmit data on the intensity, duration, and location of the stimulus. Generally speaking (though there are exceptions), the quality of a sensation is determined by which type of specialized nerve ending or receptor cell is stimulated, but the perceptual intensity (brightness, loudness, etc.) depends on how strongly the receptor is stimulated.

However, there is not perfect congruence between particular individual sensory receptors and the qualia - the units of subjective experience. For example, our retina contains just three types of cone receptor cell which have slightly different but overlapping spectral absorption. The large number of different colours that we can distinguish are somehow derived by the brain from the relative strength of the signals from these three basic detectors.

pain is usually thought of as rather different from other modalities, in that it bears no simple relationship to the physical world. It is, most simply, a perception resulting from a noxious stimulus — one associated with actual or potential tissue damage. But pain may be caused by excessive stimulation of receptors ordinarily involved with other modalities: for example heat on the skin is felt as heat, but excessive heat is felt also as pain.

Although, strictly, sensation refers only to conscious feelings, it is clear that much of the massive, unremitting inflow of information from sensory nerves does not enter consciousness. Even for the special senses, we are aware at any moment only of what we attend to, which is a tiny fraction of the information streaming in. Indeed, much sensory processing, essential for the regulation of the body, is entirely unconscious. The receptors in muscles, joints and tendons, some of which give rise to conscious proprioception, are involved in the constant, unconscious task of regulating posture and guiding movement. The heart, lungs, and major blood vessels have a variety of specialized sensory endings, conveying information to the brain about the pressure and composition of the blood, and about the stretching of the lungs. Within the brain itself, the hypothalamus and parts of the medulla contain sensory nerve cells that are specialized to detect such properties as the acidity of the blood, its temperature and the concentration of glucose, salt and other constituents. These unconscious sensory systems play an essential part in homeostasis — the maintenance of the internal environment of the body, by initiating reflex regulation of breathing, heart rate, blood vessel size, sweating and shivering, as well as in regulating essential behaviour such eating and drinking.

Psychologists and philosophers often draw a distinction between sensation (said to have a raw, unprocessed quality) and perception, the interpreted meaning of sensory activity. This view can be traced to Immanuel Kant's ‘transcendental’ philosophy, namely to the view that knowledge of the world arises from sensory experience, furnished by the mind with such ‘archetypal’ properties as space, time, relation, and causality.

The distinction between sensation and perception is hard to defend on the basis of what we now know about how sensory receptors and their associated brain areas work. At each stage, even at the sensory receptors themselves, the particular, selective characteristics of the nerve cells impose expectation and order on sensory signals. The detection of stimuli and their cognitive interpretation, to provide knowledge of the world, are inextricably linked within our sensory systems. Effortless though our perceptions seem, they involve immense ‘computational’ tasks. More than half of the human cerebral cortex is devoted to analysing sensory signals.

‘Common sense’, meaning native intelligence, derives from the medieval term sensus communis. This described the place in the fluid-filled chambers of the brain at which signals from all the sense organs were supposed to mix together, to provide the ingredients of imagination and rational thought. The near-miraculous process that intervenes between the irritation of the membrane of a sensory receptor and our perception of the world is arguably the most intelligent thing that we do.

— Colin Blakemore

See also cerebral cortex; cerebral ventricles; hearing; pain; perception; proprioception; sensory receptors; somatic sensation; taste and smell; vestibular system; visceral sensation; vision

noun

1. The capacity for or an act of responding to a stimulus: feeling, sense, sensibility, sensitiveness, sensitivity, sentiment. See awareness/unawareness.
2. A condition of intense public interest or excitement: brouhaha, stir¹, uproar. Informal to-do. Slang hoo-hah. See excite/bore/interest.
3. One that evokes great surprise and admiration: astonishment, marvel, miracle, phenomenon, prodigy, stunner, wonder, wonderment. Idioms: one for the books, the eighth wonder of the world. See good/bad.

Sensations are things like tickles, itches, pains, felt cold and heat, etc. The occurrence of a sensation is the most fundamental modification of consciousness, and shares all the problems of that concept. It is usually thought of as a primitive inner event distinguished only by its raw feel to the possessor. Sensations are distinguished from thoughts and perceptions, which carry a content with them, although the relation between the bare occurrences that make up sensations and these cognitive states is intensely debated. The private language argument of Wittgenstein is one attempt to overthrow the idea that our knowledge of our own sensations is private, infallible, and a foundation of all the rest of our knowledge. See also perception, qualia.

An irreducible sensory experience such as might occur when a sensory receptor is stimulated. Theoretically, a sensation is devoid of conscious meaning until the process of perception has taken place.

A feeling or impression that enters the consciousness from an applied stimulus. Various receptor sites are located throughout the body and react to these stimuli. Nerve impulses pass through neurons and eventually send most of the information to the sensory areas in the cerebral cortex, eliciting a conscious response. One exception is olfaction. The nose first sends impulses to the limbic system, a ring-shaped area in the center of the brain correlating with autonomic functions (breathing, heartbeat, glandular secretions), emotions, and the sense of smell. For this reason, the sense of smell seems to be the most fundamental of all of the five senses in that it is hot-wired into our most basic maintenance mechanisms. By comparison impulses relaying the sensation of taste and texture go through the brain stem to the thalamus then on to the sensory area of the cerebral cortex.

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An impression produced by impulses conveyed by an afferent nerve to the sensorium. Includes cold, distention, hunger, itch, pain, taste of various kinds, thermal, thirst, tickle, touch, warmth and some psychological and emotional experiences which animals obviously experience but cannot describe. See also sense.

• s. disturbance — cutaneous sensation errors include paresthesia, hyperesthesia, anesthesia. See also blindness, deafness.

(sensā′shən)
n

An impression conveyed by an afferent nerve to the sensorium commune.

For a list of words related to sensation, see:

• Mental States, Processes, and Behavior - sensation: sense impression of sight, sound, smell, taste, or touch and resultant feelings
• Affectionate Reference

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  See crossword solutions for the clue Sensation.

Dansk (Danish)
n. - sansefornemmelse, fornemmelse, sanseindtryk, sensation, opsigt

Nederlands (Dutch)
sensatie, gewaarwording, gevoel, opschudding

Français (French)
n. - sensation, sentiment, perception, personne formidable

Deutsch (German)
n. - Gefühl, Sensation, Aufsehen

Ελληνική (Greek)
n. - αίσθηση, σάλος, πάταγος, ντόρος

Italiano (Italian)
sensazione

Português (Portuguese)
n. - sensação (f)

Русский (Russian)
ощущение, восприятие, сенсация

Español (Spanish)
n. - sensación, sentimiento, percepción

Svenska (Swedish)
n. - uppseende, sensation, förnimmelse, känsla, sinnesförnimmelse

中文（简体）(Chinese (Simplified))
感觉, 知觉, 轰动, 激动, 感觉能力, 知觉作用, 轰动的事件

中文（繁體）(Chinese (Traditional))
n. - 感覺, 知覺, 轟動, 激動, 感覺能力, 知覺作用, 轟動的事件

한국어 (Korean)
n. - 감각, 느낌, 센세이션

日本語 (Japanese)
n. - 感覚, 知覚, 感情, 感動, 興奮, 大評判, 大騒ぎ

العربيه (Arabic)
‏(الاسم) أحساس, , شعور‏

עברית (Hebrew)
n. - ‮הרגשה, תחושה, חישה, התרגשות, הפתעה גדולה, סנסציה‬