5
Transformation:
The Miracle of Sensation
Joseph McNair
Reality, according to Edmund B. Bolles is a “jumble of sensations and details” (Bolles, 1991, p. 53). Our senses bring to us a deluge of information about our world. Sensation combines several processes:
· the mechanical stimulation of sensory receptors located in the various sense organs by physical stimuli—light, sound, smell, taste or touch;
· the conversion of that stimuli by those sensory receptors into electrochemical energy and the transmission of that energy to the cerebral cortex of brain; and
· the conversion of that energy into mental images or symbols for a variety of mental manipulations beginning with analysis and interpretation.
Worchel, S and Shebilski, W. 1989, p. 142
According to Robert E. Ornstein (1985):
The senses routinely perform two miracles. First, each sensory organ acts to transform a particular kind of physical energy--the short waves of light, the molecules of sourness--into a different kind of energy, the electrochemical process of neural firing.
This process is called transduction. Each sense has specialized receptors responsible for the transduction of external energy into the language of the brain. The eye transduces light, the ear transduces sound waves, the nose transduces gaseous molecules.
Second, at some point in the sensory and brain system, there is a second transformation:
the billions of electrical explosions and chemical secretions of “neural firing” become trees and cakes, silverfish and laughter—the conscious world of human experience (Ornstein p. 34).
The miracle of seeing depends on the functions of several structures in and around the eyeball.
http://www.yorku.ca/eye/brain2.htm
Image created by author ear.jpg
The miracle of hearing begins when sound waves enter the ear.
The Anatomy of the Ear
Adapted from http://www.earaces.com/anatomy.htm#Basilar%20Membrane:
Adapted from http://www.earaces.com/anatomy.htm#Basilar%20Membrane:
http://www.colorado.edu/epob/epob1220lynch/image/figure6j.jpg
Jeff Goldberg (2003) puts it a bit more simply:
In humans and other mammals, hair cell bundles are arranged in four long, parallel columns on a gauzy strip of tissue called the basilar membrane. This membrane, just over an inch long, coils within the cochlea, a bony, snail-shaped structure about the size of a pea that is located deep inside the inner ear. Sound waves generated by mechanical forces, such as a bow being drawn across a string, water splashing on a hard surface, or air being expelled across the larynx, cause the eardrum—and, in turn, the three tiny bones of the middle ear—to vibrate. The last of these three bones (the stapes, or "stirrup") jiggles a flexible layer of tissue at the base of the cochlea. This pressure sends waves rippling along the basilar membrane, stimulating some of its hair cells.
These cells then send out a rapid-fire code of electrical signals about the frequency, intensity, and duration of a sound. The messages travel through auditory nerve fibers that run from the base of the hair cells to the center of the cochlea, and from there to the brain. After several relays within the brain, the messages finally reach the auditory areas of the cerebral cortex, which process and interpret these signals as a musical phrase, a dripping faucet, a human voice, or any of the myriad sounds in the world around us at any particular moment.
Goldberg, J. 2003, The Quivering Bundles That Let Us Hear: Signals From a Hair Cell, [online][URL] http://www.hhmi.org/senses/c110.html
THE NOSE
http://www.planregionalpress.co.uk/perspectives/images/nose.jpg
The miracle of smell begins when gaseous molecules floating on the air we breathe enter the nose. These gaseous molecules are called odorants.
adapted by author from http://info.med.yale.edu/caim/cnerves/cn1/cn1_2.html
Adapted by author from http://sun.science.wayne.edu/~wpoff/cor/sen/smelanat.html
http://www.driesen.com/olfactorysystem.jpg
Maya Pines in an article entitled “The Vivid World of Odors” writes:
After taking a mixture of mind-altering drugs one night, Stephen D., a 22-year-old medical student, dreamed that he had become a dog and was surrounded by extraordinarily rich, meaningful smells. The dream seemed to continue after he woke up—his world was suddenly filled with pungent odors.
Walking into the hospital clinic that morning, "I sniffed like a dog. And in that sniff I recognized, before seeing them, the twenty patients who were there," he later told neurologist Oliver Sacks. "Each had his own smell-face," he said, "far more vivid and evocative than any sight-face." He also recognized local streets and shops by their smell. Some smells gave him pleasure and others disgusted him, but all were so compelling that he could hardly think about anything else.
The strange symptoms disappeared after a few weeks. Stephen D. was greatly relieved to be normal again, but he felt "a tremendous loss, too," Sacks reported in his book The Man Who Mistook His Wife for a Hat and Other Clinical Tales. Years later, as a successful physician, Stephen D. still remembered "that smell-world—so vivid, so real! It was like a visit to another world, a world of pure perception, rich, alive, self-sufficient, and full...I see now what we give up in being civilized and human." Pines, M. 2003, The Vivid World of Odor, [online[URL] http://www.hhmi.org/senses/d110.html
http://www.inkwellgallery.com/images/entertainment/music/simmonsg-1a.jpg
The miracle of taste begins when molecules of substances come in contact with sensory receptor cells on the tongue called taste buds and register as sweet, salty, sour, bitter and umami.
1. Tasted substances are “broken down” –dissolved-- in saliva before they can stimulated the taste buds.
2. Saliva brings the dissolved chemicals [molecules] to the taste buds. Saliva is essential to taste buds working. In the absence of saliva, taste buds do not work well.
3. Various kinds of chemical taste buds are located below the surface of the "bumps" (called papillae) that cover the surface of the tongue. These papillae create rough surface that helps to keep food within the mouth.
4. Molecules of food or tastants interact either with proteins on the surfaces of the taste buds or with pore-like proteins called ion channels. These interactions trigger neural firings which send chemical signals via three nerves, the facial, vagus and the glossopharyngeal nerves, to the gustatory nuclei of the medulla, then to the ventral posterior nucleus of the thalamus, and finally to the primary and secondary gustatory cortex.
Adapted by author from Tutorial 29: Sense of Taste, 2003,[online][URL] http://psych.athabascau.ca/html/Psych402/Biotutorials/29/part1.html
http://psych.athabascau.ca/html/Psych402/Biotutorials/29/part1.html
David V. Smith and Robert F. Margolskee (2003) in an article in the Scientific American entitled “Making Sense of Taste” write:
Taste cells lie within specialized structures called taste buds, which are situated predominantly on the tongue and soft palate. The majority of taste buds on the tongue are located within papillae, the tiny projections that give the tongue its velvety appearance. (The most numerous papillae on the tongue--the filiform, or threadlike, ones--lack taste buds, however, and are involved in tactile sensation.) Of those with taste buds, the fungiform ("mushroomlike") papillae on the front part of the tongue are most noticeable; these contain one or more taste buds. The fungiform papillae appear as pinkish spots distributed around the edge of the tongue and are readily visible after taking a drink of milk or placing a drop of food coloring on the tip of the tongue. At the back of the tongue are roughly 12 larger taste bud–containing papillae called the circumvallate ("wall-like") papillae, which are distributed in the shape of an inverted V. Taste buds are also located in the foliate ("leaflike") papillae, small trenches on the sides of the rear of the tongue.
Taste buds are onion-shaped structures of between 50 and 100 taste cells, each of which has fingerlike projections called microvilli that poke through an opening at the top of the taste bud called the taste pore. Chemicals from food termed tastants dissolve in saliva and contact the taste cells through the taste pore. There they interact either with proteins on the surfaces of the cells known as taste receptors or with pore-like proteins called ion channels. These interactions cause electrical changes in the taste cells that trigger them to send chemical signals that ultimately result in impulses to the brain.
Smith, D.V. and Margolskee, R.F., 2003, Making Sense of Taste http://www.sciam.com/article.cfm?articleID=000641D5-F855-1C70-84A9809EC588EF21
http://www.sciam.com/article.cfm?articleID=000641D5-F855-1C70-84A9809EC588EF21
Tim Jacob adds (2003):
Taste drives appetite and protects us from poisons. So, we like the taste of sugar because we have an absolute requirement for carbohydrates (sugars etc.). We get cravings for salt because we must have sodium chloride (common salt) in our diet. Bitter and sour cause aversive [causing avoidance by using an unpleasant or punishing stimulus]… reactions because most poisons are bitter (most bitter substances are bad for you -- certainly in excess) and off food goes sour (acidic). Why do medicines all taste bitter? Because they are, in fact, poisons and if you take too much they will harm you. We have an absolute need for protein, and amino acids are the building blocks for proteins, so the "new" taste quality umami (pronounced: oo-mami), which is the meaty, savory taste drives our appetite for amino acids. This taste has been known to the Japanese for a long time - but has only recently been recognized by the West. Bacon really hits our umami receptors because it is a rich source of amino acids.
Jacob, T., 2003, Taste - A brief tutorial, [online][URL] http://www.cf.ac.uk/biosi/staff/jacob/teaching/sensory/taste.html
http://www.wingsofknowledge.com/images/aczun5.jpg
“Touch” is the name given to sensations caused by a network of nerve endings or sensory receptor cells that reach just about every part of our body via the skin. These sensory receptor cells are located just below the surface of the skin and register light and heavy pressure and differences in temperature. There are at least six types of touch receptors. One that registers hot, one that registers cold, one that registers pain, one for pressure, one for heavy touch, and one for light or fine touch.
The miracle of touch begins when
1. physical stimuli make contact with these sensory receptor cells in the bottom layer of our skin called the dermis. The dermis is filled with several kinds of sensory receptors which encode information about the various stimuli which comes in contact with the skin into neural impulses. There are two paths to the primary and secondary somatosensory [touch, temperature, pressure, pain] cortexes
2. Fine touch sensations and kinesthetic sensations from the muscles and internal organs are carried to the spinal cord via the dorsal root nerve.
3. In the spinal cord the impulses ascend through the dorsal columns to the dorsal column nuclei in the medulla.
4. From there they go through the medial lemniscus to the ventral posterior nucleus (VPN) in the thalamus.
5. From the VPN in the thalamus, the majority of the impulses go to the primary somatosensory cortex while the remaining go to the secondary somatosensory cortex of the posterior parietal lobe.
6. Temperature and pain sensations are carried to the spinal cord via the dorsal root nerve.
7. The majority of these neural impulses ascend to the brain via the anterolateral [in front and away from the middle line] portion of the spinal cord either to the thalamus, through the mid brain, or through the brain stem to the primary somatosensory cortex and the secondary somatosensory cortex.
http://psych.athabascau.ca/html/Psych402/Biotutorials/28/part1.html
Our bodies have about twenty (20) different types of sensory receptors that all send messages to our brains. However, the most common receptors are the touch receptors, or heat, cold, pain, pressure, light and heavy touch. Pain receptors are probably the most important for personal safety because they warn the brain that our bodies are hurt or injured.
Some areas of the body are more sensitive than others because they have more nerve endings. The tips and the sides of our tongues have a lot of sensory receptor cells very sensitive to pain. The tongue, however, is not as good at sensing hot or cold. That is why it is so easy to burn our mouths when we eat something really hot.
Fingertips are also very sensitive. The fingertips can be “taught” to read Braille by feeling the patterns of raised dots on their paper.
http://users.tpg.com.au/users/amcgann/body/senses/large_skin.gif
http://newdeal.feri.org/images/t14.gif
Closely related to the sense of touch (some believe it to be a part of the touch or haptic system) is the kinesthetic sense. Kinesthesis is the ability we have to sense body position and the movement of muscles, tendons, and joints. The kinesthetic sensory receptor cells are called proprioceptors and are special nerve-cells receiving stimuli attached to muscles, tendons, and joints. They measure, for example,
· the activity of muscles,
· the stressing of tendons,
· the position of the skin, relative to the touched surface and
· the angle position of joints
Within the labyrinth, a system of cavities in the inner ear, are the receptors for the auditory and vestibular systems. The vestibular system is the part of the ear that is responsible for our sense of balance. According to Tutis Villis:
The vestibular system has two parts: the otoliths and the semicircular canals. Each has different functions. The otoliths have two functions:
The semi-circular canals sense the head’s angular motion (eg rotation to the right).
http://weboflife.ksc.nasa.gov/images/vestibularFig2.gif
According Schomaker, et al (1995:
These organs […the semi-circular canals and the otoliths…] have a radius of a little less than a millimeter. They are used by the brain to sense movement of your head. You can demonstrate this for yourself by moving your head from side to side. As you move your head the output of the vestibular organ (from the afferent nerve) is processed by the brain, and the eyes are made to move in a compensatory way such that your gaze remains fixed. This even happens when yours eyes are closed, so it is not visual clues that are being used by the brain.
The inner ear also lets your brain compensate for movements of the body in visual processing. As you move your head (and your eyes with it - for example when walking), even though the image on your retina is moving, your mind correctly perceives that you are moving, and that the world is fixed. A large part of the information about your movement is taken from the vestibular organ. To see this in play, try moving your eye gently with your finger, as your eye moves (with no compensating signal from the vestibular organ), it seems as if the world is shaking. Without feedback from the vestibular organ, your visual perceptions fail.
Kinesthesis supports the perception of the sense organs. If some informations delivered by a sense organ and by kinesthesis are contradictory, the brain will prefer the information coming up from the sense organ.
Schomaker, L., Nijtmans J.,Camurri, A., Lavagetto, F., Morasso , P., Benoît, C., Guiard-Marigny, T., Le Goff, B., Robert-Ribes, J., Adjoudani , A., Defée, I. Münch, S., Hartung, K., Blauert, J., 1995, A Taxonomy of Multimodal Interaction in the Human Information Processing System http://hwr.nici.kun.nl/~miami/taxonomy/node21.html
Beth Azar (1998) writing for the American Psychological Association “Monitor” tells of how one man’s loss of sensation provides answers to questions about touch and movement:
Until Ian Waterman was 19, he, like most every one else, thought little about his ability to sense the position and movement of his body. What 19th-century neuroanatomist Sir Charles Bell called the 'sixth sense' and what psychophysicists call proprioception and now consider a part of the haptic, or touch system, is so unconscious that few people realize it’s there.
Waterman’s obliviousness to that sense ended when a viral infection destroyed the nerves that control his sixth sense as well as those for feeling light touch. He’s lost all feeling below the neck and is unable to tell without looking how his body is positioned.
That was 1972 and even Waterman’s doctors had a hard time understanding the extent of his disability.
Through trial and error over three years, Waterman, who lives in Hampshire, England, taught himself how to move again by consciously controlling and visually monitoring every action. To this day, if the lights go out unannounced, he crumples to the floor, unable to budge until they come back on. It’s almost impossible for most people to imagine his condition, he admits.
'How can one explain a total loss of proprioception—a sense most people don’t even know they have?' he is quoted as saying in 'Pride and a Daily Marathon' (MIT Press, 1995), the book neurophysiologist Jonathan Cole, MD, wrote about his condition.
Cole, of Poole Hospital, Poole England and Southampton University, met Waterman in 1986 and was the first physician to take a true interest in the case and Waterman’s plight. 'Before I met Jonathan, I often thought I might be mad,' says Waterman. 'No one understood what was wrong or why life was such a struggle.'
Now, many researchers, including psychologists, are fascinated not only by Waterman’s physical disorder but also by his ability to compensate for his loss. His case brings to life the critical importance of the sense of proprioception and touch, says psychologist Michael Turvey, Ph.D, who studies touch at the University of Connecticut … 'The haptic senses underlie almost everything we do that involves movement,' he says. 'At the same time, Waterman is able to do more than many theories of touch and movement would predict.'
The case represents a unique opportunity to test theories of touch, proprioception and movement that would be impossible otherwise, say researchers. They are able to examine how a total lack of feedback from the outside world affects how a person moves about in and interacts with the environment.
Cases like Waterman’s are remarkable in the precision of the damage: Waterman lost none of the nerves that control muscle movement and he is still able to feel temperature, pain, deep pressure and muscle fatigue (see chart on page 20). He has lost all of the cutaneous nerves that provide the skin with the sense of touch and all of the nerves attached to muscles and tendons that provide a sense of joint and limb position.
His recovery is equally unique. Although his movements can look mechanical, it’s often hard to tell there’s anything wrong unless something unexpected happens and he’s thrown off balance, say those who have met him.
Azar, B., 1998. Why can’t this man feel whether or not he’s standing up?, [online][URL] http://www.apa.org/monitor/jun98/touch.html
We have made a cursory examination of six (6) sensory systems. It should be clear that sensation is the “input” phase of a larger information processing process. Referring back to Essay #4, "Transformation: Awareness and Consciousness", to be conscious means in part to be able to mentally select individual sensations, combine them into individually distinct phenomena (people, objects, events) and to discover their identity. This act of selecting, combining and identifying sensations is the second miracle routinely performed by the senses, a part of the process we call perception.
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