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Sensation and Perception. Importance of sensory systems of the organism and their role in behavior. Sensitivity training.
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Sensation and Perception. Importance of sensory systems of the organism and their role in behavior
Sensitivity training • The techniques employed by Kurt Lewin at the National Training Laboratoriesin Maine and hiscolleagues, collectively known as sensitivity training,were widely adopted for use in a variety of settings. • Initially,they were used to train individuals in business, industry,the military, the ministry, education, and otherprofessions. In the 1960s and 1970s, sensitivity trainingwas adopted by the human potential movement, whichintroduced the “encounter group.” • Although encountergroups apply the basic T-group techniques, they emphasizepersonal growth, stressing such factors as self-expressionand intense emotional experience.
Vision is the process of transforming light energy into neuralimpulses that can then be interpreted by thebrain.
The rods an cones • The retina, lining the back of the eye, consists of tenlayers of cells containing photoreceptors (rods and cones)that convert the light waves to neural impulses through aphotochemical reaction. Aside from the differences inshape suggested by their names, rod and cone cells containdifferent light-processing chemicals (photopigments),perform different functions, and are distributeddifferently within the retina. • Cone cells, which providecolor vision and enable us to distinguish details, adaptquickly to light and are most useful in adequate lighting.Rod cells, which can pick up very small amounts of lightbut are not color-sensitive, are best suited for situations inwhich lighting is minimal. Because the rod cells are activeat night or in dim lighting, it is difficult to distinguishcolors under these circumstances. Cones are concentratedin the fovea, an area at the center of the retina, whereasrods are found only outside this area and become morenumerous the farther they are from it. Thus, it is more difficultto distinguish colors when viewing objects at theperiphery of one’s visual field.
Processing the visual information • Branches ofthe optic nerve cross at a junction in the brain in front ofthe pituitary gland and underneath the frontal lobescalled the optic chiasm and ascend into the brain itself.The nerve fibers extend to a part of the thalamus calledthe lateral geniculate nucleus (LGN), and neurons fromthe LGN relay their visual input to the primary visualcortex of both the left and right hemispheres of the brain,where the impulses are transformed into simple visualsensations. • Objects in the left visual field are viewedonly through the right brain hemisphere, and vice versa.The primary visual cortex then sends the impulses toneighboring association areas which add meaning or “associations”to them.
The field of vision • A human has a field of vision that covers almost 180°, although binocularvision is limited to the approximately 120° common to both eyes. The fieldextends upward about 60° and down about 75° • Because the nerve fibers from the left half of the retina of the left eye go tothe left side of the brain and fibers from the left half of the right eye crossthe optic chiasm and go to the left side of the brain as well, all theinformation from the two left half-retinas ends up in the left half of the brain. • And because the lens of the eye reverses the image it sees, it is informationfrom the right half of the visual field that is going to the left visual cortex.Likewise, information from the left half of the visual field goes to the rightvisual cortex.
Binocular vision • Binocular depth cues are based on the simple factthat a person’s eyes are located in different places. • Onecue, binocular disparity, refers to the fact that differentoptical images are produced on the retinas of both eyeswhen viewing an object. • By processing informationabout the degree of disparity between the images it receives,the brain produces the impression of a single objectthat has depth in addition to height and width.
Hearing • Hearing is the ability to perceive sound.The ear, the receptive organ for hearing, has threemajor parts: the outer, middle, and inner ear. The pinna orouter ear—the part of the ear attached to the head, funnelssound waves through the outer ear. • The sound wavespass down the auditory canal to the middle ear, wherethey strike the tympanic membrane, or eardrum, causingit to vibrate. These vibrations are picked up by threesmall bones (ossicles) in the middle ear named for theirshapes: the malleus (hammer), incus (anvil), and stapes(stirrup). • The stirrup is attached to a thin membranecalled the oval window, which is much smaller than theeardrum and consequently receives more pressure.
Hearing • As the oval window vibrates from the increasedpressure, the fluid in the coiled, tubular cochlea (innerear) begins to vibrate the membrane of the cochlea (basilarmembrane) which, in turn, bends fine, hairlike cellson its surface. • These auditory receptors generate miniatureelectrical forces which trigger nerve impulses thatthen travel via the auditory nerve, first to the thalamusand then to the primary auditory cortex in the temporallobe of the brain.
Touch sensation • Touch is the skin sense that allows us to perceive pressureand related sensations, including temperature andpain. • The sense of touch is located in the skin, which iscomposed of three layers: the epidermis, dermis, and hypodermis. • Different types of sensory receptors, varyingin size, shape, number, and distribution within the skin,are responsible for relaying information about pressure,temperature, and pain.
Sensory receptors encode various types of informationabout objects withwhich the skin comes in contact.We can tell how heavy an object is by both thefiring rateof individual neurons and by the number of neuronsstimulated. (Boththe firing rate and the number of neuronsare higher with a heavier object.)Changes in the firingrate of neurons tell us whether an object is stationaryor vibrating, and the spatial organization of the neuronsgives us information about its location.
Pain • Pain is physical suffering resulting from some sort of injuryor disease, experienced through the central nervoussystem. • Pain is a complex phenomenon that scientists arestill struggling to understand. Its purpose is to alert thebody of damage or danger to its system, yet scientists donot fully understand the level and intensity of painsometimes experienced by people. Long-lasting, severepain does not serve the same purpose as acute pain,which triggers an immediate physical response. • Painthat persists without diminishing over long periods oftime is known as chronic pain. It is estimated that almostone-third of all Americans suffer from some formof chronic pain.
Spreading of pain information in the body • Pain signals travel through the body along billionsof special nerve cells reserved specifically for transmittingpain messages. These cells are known as nociceptors. • The chemical neurotransmitters carrying the messageinclude prostaglandins, bradykinin—the mostpainful substance known to humans—and a chemicalknown as P, which stands for pain. Prostaglandins aremanufactured from fatty acids in nearly every tissue inthe body. Analgesic pain relievers, such as aspirin andibuprofen, work by inhibiting prostaglandin production.
Spreading of pain information in the body • As they travel, the pain messages are sorted accordingto severity. Recent research has discovered that thebody has two distinct pathways for transmitting painmessages. • The epicritic system is used to transmit messagesof sudden, intense pain, such as that caused by cutsor burns. The neurons that transmit such messages arecalled A fibers, and they are built to transmit messagesquickly. • The protopathic system is used to transmit lesssevere messages of pain, such as the kind one might experiencefrom over-strenuous exercise. The C fibers ofthe protopathic system do not send messages as quicklyas A fibers.
The smelland the taste • Olfaction is one of the two chemical senses: smelland taste. Both arise from interaction between chemicaland receptor cells. • In olfaction, the chemical is volatile,or airborne. Breathed in through the nostrils or taken invia the throat by chewing and swallowing, it passesthrough either the nose or an opening in the palate at theback of the mouth, and moves toward receptor cells locatedin the lining of the nasal passage. As the chemicalmoves past the receptor cells, part of it is absorbed intothe uppermost surface of the nasal passages called the olfactoryepithelium, located at the top of the nasal cavity.
The smelland the taste • When a person eats, chemical stimuli taken inthrough chewing and swallowing pass through an openingin the palate at the back of the mouth and move towardreceptor cells located at the top of the nasal cavity,where they are converted to olfactory nerve impulses thattravel to the brain, just as the impulses from olfactorystimuli taken in through the nose. • The olfactory and gustatorypathways are known to converge in various partsof the brain, although it is not known exactly how thetwo systems work together.
Sensory deprivation • Sensory deprivation experiments of the 1950s haveshown that human beings need environmental timulationto function normally. In a classic early experiment,college students lay on a cot in a small, empty cubiclenearly 24 hours a day, leaving only to eat and use thebathroom. • They wore translucent goggles that let in lightbut prevented them from seeing any shapes or patterns,and they were fitted with cotton gloves and cardboardcuffs to restrict the sense of touch. • The continuous humof an air conditioner and U-shaped pillows placedaround their heads blocked out auditory stimulation.
Sensory deprivation • Initially, the subjects slept, but eventually they becamebored, restless, and moody. They became disorientedand had difficulty concentrating, and their performanceon problem-solving tests progressively deterioratedthe longer they were isolated in the cubicle. • Some experiencedauditory or visual hallucinations. Althoughthey were paid a generous sum for each day they participatedin the experiment, most subjects refused to continuepast the second or third day. • After they left the isolationchamber, the perceptions of many were temporarilydistorted, and their brain-wave patterns, which hadslowed down during the experiment, took several hoursto return to normal.
Sensory deprivation • The deterioration in both physical and psychologicalfunctioning that occurs with sensory deprivation has beenlinked to the need of human beings for an optimal level ofarousal. • Too much or too little arousal can produce stressand impair a person’s mental and physical abilities. Thus,appropriate degrees of sensory deprivation may actuallyhave a therapeutic effect when arousal levels are too high. • A form of sensory deprivation known as REST (restrictedenvironmental stimulation), which consists of floating forseveral hours in a dark, soundproof tank of water heatedto body temperature, has been used to treat drug andsmoking addictions, lower back pain, and other conditionsassociated with excessive stress.
