CHAPTER 3 (Sensation and Perception) Michael L. Farris Psychology 101
Subliminal Persuasion • Famous Attempt at Subliminal Advertising: • New Jersey theater • “Eat Popcorn” & “Drink Coca-Cola” • Words appeared for 1/3000 of a second every 5 seconds • At that speed, they were below the normal threshold for awareness. • During the 6 weeks the messages ran, the firm claimed increases in popcorn and Coca-Cola sales. • What do you think? Did the sales increase because of the subliminal messages, or something else? Please see pages 108, 117 & 118 in your text for more information.
Backmasking • In another uproar over subliminal perception, critics charged that spoken messages recorded backward (called “backmasking”) in rock music are perceived unconsciously by listeners. • Queen (Another One Bites the Dust) • The Beatles (White Album) Experiment: Vokey and Read recorded a variety of sentences backward, including selections from Lewis Carrol’s “Jabberwocky” and the 23rd Psalm from the Bible. Their tests clearly showed that the backward sentences were not recognized. Still, shopping malls sometimes use subliminal messages embedded in the music (“Don’t Steal”, “Buy More”, Orange Julius Rules”) Conclusion: There is little evidence that subliminal messages greatly influence behavior. P.118.
Sensitivity • Sensation: The incoming flow of information from the environment. P.84. • Perception: The process by which the brain organizes sensations into meaningful patterns or representations of the world. (p.106) • Hearing is much more sensitive than taste • A voice or musical instrument that is off pitch 1/3 of 1% will be noticeable. • For taste, a 20% change is necessary to produce a JUST NOTICEABLE DIFFERENCE (p.84). • If a cup of coffee has 5 teaspoons of sugar in it, 1 more (1/5 of 5) must be added before you would notice an increase in sweetness. • Just Noticeable Difference: Any noticeable difference in a stimulus. • Absolute Threshold: The minimum amount of physical energy necessary to produce a sensation.
Absolute Thresholds Sensory ModalityAbsolute Threshold Vision Candle flame seen at 30 miles on a clear, dark night Hearing Tick of watch under quiet conditions at 20 feet Taste 1 teaspoon of sugar in 2 gallons of water Smell 1 drop of perfume diffused into a three-room apartment Touch A bee’s wing falling on your cheek from 1 cm above Please see pages 84-85 in your text for more information.
Vision Problems (P.87-93) The shape of the eye affects focusing. • Hyperopia (farsightedness): If the eye is too short, nearby objects cannot be focused, but distant objects are clear. • Myopia (nearsightedness): If the eyeball is too long, the image falls short of the retina, and distant objects cannot be focused. • Astigmatism: When the cornea or the lens is misshapen, part of the visual field will be focused, and part will be fuzzy. In this case, the eye has more than one focal point. All three visual defects can be corrected by placing glasses or contact lenses in front of the eye. These added lenses change the path of incoming light to restore crisp focusing. As people age, the lens becomes less flexible and less able to accommodate. Since the les must do its greatest bending to focus nearby objects, the result is presbyopia, or farsightedness due to aging. Perhaps you have seen a grandparent reading a newspaper at arm’s length because of presbyopia. If you now wear glasses for farsightedness (myopia), you may need bifocals as you age. (Unless your arms grow longer in the meantime.)
Accommodation • Accommodation (p.88): The process of adjusting the configuration of the lenses to bring images into focus on the retina. • Try the “cocktail sausage” demonstration. Hold both index (pointer) fingers at arms length, pointing at each other. • Leave a 6 inch gap, and focus on the wall through the gap. Slowly bring the fingers together, staring at the wall through the gap. • Stop just before your fingers touch. See the sausage? Yum!
Rods and Cones • Rods: Rod-shaped receptors in the retina which predominate in low (dim) light conditions. Species active only at night tend to have rod-only retinas. Peripheral visionis mainly rod vision, and occurs at the edges of the visual field. At night, the most visible color to our rods is blue or blue-green. That’s why police use blue lights! • Cones: Receptors in the retina that predominate in good (bright) lighting, and provide high-acuity (finely detailed) colored perceptions of the world. In dim illumination, there is not enough light to reliably excite the cones, and the more sensitive rod-mediated vision predominates. The most visible color to cones is yellowish green. That’s why some fire trucks and roadside work crew vests are this color! • An area at the center of the retina containing only cones is called the Fovea. Please see pages 88-89 in our text for more information.
Color Blindness • A person who is color blind cannot perceive colors (the world looks like a black and white movie). How do we know? • In a few rare cases, people have been color blind in only one eye and can compare. • Two colors of equal brightness look exactly alike to the color blind individual. • The color blind person either lacks cones or has cones that do not function normally. • Color blindness is caused by changes in the genes that control red, green, and blue pigments in the cones. Please see pages 92-93 in our text for more information.
ColorblindTest • If picture A looks like number 3, and picture B looks like number 73, you're ok. If picture A looks like number 5 and picture B looks like nothing at all, you may have a deficiency in your color vision ! • Red-green color blindness is a recessive, sex-linked trait. That means it is carried on the X, or female, chromosome. Women have two X chromosomes, so if they receive only one defective color gene, they still have normal color vision. • Color blind men, however, have only one X chromosome, so they can inherit the defect from their mothers (who are usually not color blind themselves). • The red-green color blind person sees both reds and greens as the same color, usually as a yellowish brown.
Dark Adaptation Dark Adaptation (Coon, p.170) is the dramatic increase in retinal sensitivity to light that occurs in darkness. If you enter a dark movie theatre on a sunny day, you practically need to be led to your seat. After a short time, however, you begin to see the entire room in detail. Studies show that it takes about 30-35 minutes of complete darkness to reach maximum visual sensitivity. A completely dark-adapted eye is 100,000 times more sensitive to light. At that point, the human eye is almost as light sensitive as the eyes of an owl!
Blind Spot • Blind Spot (pgs.89-90): The gap in the receptor layer of the retina where the bundle of retinal ganglion cell axons leave the eye. There are no rods or cones where the optic nerve leaves the eye. • One of the most dramatic experiments to perform is the demonstration of the blind spot. The blind spot is the area on the retina without receptors that respond to light. Therefore an image that falls on this region will NOT be seen.It is in this region that the optic nerve exits the eye on its way to the brain. To find your blind spot, look at the image below or draw it on a piece of paper:
Blind Spot Demonstration • To draw the blind spot tester on a piece of paper, make a small dot on the left side separated by about 6-8 inches from a small + on the right side. • Close your right eye. Hold the image (or place your head from the computer monitor) about 20 inches away. • With your left eye, look at the +. Slowly bring the image (or move your head) closer while looking at the +. • At a certain distance, the dot will disappear from sight...this is when the dot falls on the blind spot of your retina. • Reverse the process. Close your left eye and look at the dot with your right eye. Move the image slowly closer to you and the + should disappear!
Complementary Colors • Complementary colors: Pairs of colors that produce white or gray when combined in equal measure (for example, red light and green light). • This is based on the opponent-process theory (Ewald Hering, 1878), which observes that complementary colors cannot exist together (there is no such thing as bluish yellow or reddish green). • Another observation is that the afterimage produced by staring at yellow is blue and vice versa. Blue is the complementary color to yellow. Red is complementary to green. (For more information, please see page 58 in the Pinel text.) A Demonstration follows with the next slide: Stare at the center of the red box for 30 seconds (or a slow count of 30). Then look at the next (blank) slide, or a white surface. What do you see?
Hearing • Any vibrating object (a tuning fork, the string of a musical instrument, or the vocal cords) will produce sound waves (cyclic, wave-like movement of air molecules). • Other materials, such as fluids or solids, can also carry sound. But sound does NOT travel in a vacuum (p.94). Movies that show characters reacting to the “roar” of alien starships or titanic battles in deep space are in error.
How We Hear • The pinna (visible outer ear) funnels sound to the tympanic membrane (ear drum), which vibrates and moves three small bones (auditory ossicles). These bones link the eardrum with the cochlea. • The cochlea (p.95), a snail shaped organ that makes up the inner ear, is the organ of hearing. • There is fluid in the cochlea, and waves in the fluid are detected by tiny hair cells, which generate nerve impulses to be sent to the brain. The bristles on hair cells, called cilia, are sensitive to movement.
Deafness • Conduction Deafness (p.97): Occurs when there is poor transfer from the eardrum to the inner ear. The eardrum or ossicles may be damaged or immobilized by disease or injury. Often, a hearing aid will overcome conduction deafness. • Nerve Deafness (p.97): Results from damage to the hair cells or auditory nerve. Hearing aids don’t help, because auditory messages are blocked from reaching the brain. However, a new type of artificial hearing system is being developed that may help. • Stimulation Deafness (p.97): Occurs when very loud sounds damage hair cells in the cochlea. Each of us starts life with about 32,000 hair cells. However, we begin losing them the moment we’re born. By age 65 more than 40% are gone. • If you work in a noisy environment or enjoy loud music, motorcycling, or similar pursuits, you (we!) may be risking stimulation deafness. • Hair cells (which are about as thick as a cobweb) are very fragile and easily damaged. • Once dead, they are never replaced. When you abuse them, you lose them.
Hearing Loss • The danger of hearing loss depends on both the loudnessof sound and how long you are exposed to it. • Daily exposure to 85 decibels or more may cause permanent hearing loss. • Even short periods at 120 decibels (a rock concert) may cause a temporary threshold shift (a partial, transitory loss of hearing). • Brief exposure to 150 decibels (a jet airplane nearby) can cause permanent deafness. • Please see page 97 for more information on Hearing Loss.
softest audible sound 0 dB normal breathing 10 dB rustling leaves20 dB whispering25 dB clothes dryer60 dB normal conversation60 dB dishwasher65 dB car70 dB busy traffic75 dB alarm clock80 dB noisy restaurant80 dB average factory85 dB screaming child90 dB subway train100 dB diesel truck100 dB jackhammer100 dB helicopter105 dB power mower105 dB shouting in ear110 dB live rock music90-130 dB football stadium117 dB band concert120 dB thunder120 dB car horn120 dB jackhammer130 dB air raid siren130 dB noisy squeeze toys135 dB PAIN STARTS 140 dB gunshot140 dB jet engine140 dB rocket launching180 dB loudest sound194 dB Decibel Levels of Common Sounds
Tinnitus • Tinnitus is a ringing or buzzing sensation following exposure to loud sounds (Coon,p.176). • If you feel or hear this ringing or buzzing, chances are good that hair cells have been damaged. • Almost everyone has tinnitus at times, especially with increasing age. But after repeated sounds that produce this warning, you can expect to become permanently hard of hearing. • A study of people who regularly went to amplified concerts found that 44% had tinnitus and most had some hearing loss (Meyer-Bisch, 1996). • The next time you are exposed to a very loud sound, remember to take precautions against damage. (Earplugs are good, and fingers are always handy in an emergency!)
Smell and Taste (p.99) • Olfaction: The sense of smell. • Gustation: The sense of taste. • 1 person out of 100 cannot smell anything at all! (Total anosmia) • Smell may seem like a minor sense that we can live without. Why is this anosmia dangerous? • Smell and taste are very closely linked. One affects the other. • Sensory Adaptation: Decreases our response to a constant or unchanging stimulus (p. 86). This is why we can’t smell something as well after a few minutes of being in a room with it. • Taste buds (the receptor organs for taste) are located mainly on the top side of the tongue, but a few are found elsewhere inside the mouth. • There are 4 basic taste sensations: • Sweet (least sensitive) • Salt (a bit sensitive) • Sour (sensitive) • Bitter (most sensitive) • Why mightbitter and sour foods be most detectable?
The Somesthetic Senses • A gymnast “flying” through a routine on the uneven bars may rely as much on the somesthetic senses as on vision (soma means “body”, esthetic means “feel”). • Somesthetic senses include: • Skin senses (touch) • Kinesthetic senses (receptors in the muscles and joints that detect body position and movement) • Vestibular senses (receptors in the inner ear for balance, gravity and acceleration). • Motion Sickness: You’ve probably seen astronauts on television, playfully enjoying weightlessness. In reality, if you were to ride into space, it is about 70% likely that you would throw up! (p.104) • Space sickness is similar to sea-sickness, air-sickness, and car-sickness. It is especially intense because weightlessness drastically alters sensations the brain receives from the head, muscles, and joints.
Motion Sickness • Motion sickness is related to the vestibular system (p.104). • Fluid filled sacs in the vestibular system (called otolithorgans) are sensitive to movement, acceleration and gravity. • The otolith organs contain tiny crystals in a soft, gelatin-like mass. The tug of gravity or rapid head movements can cause the mass to shift. This stimulates hair-like receptor cells, allowing us to sense gravity and movement through space. • The best explanation of motion sickness is the sensory conflict theory (Coon, p.181): According to this theory, dizziness and nausea occur when sensation from the vestibular system fail to match information received from the eyes and body. On solid ground, the information from the vestibular system, vision, and kinesthesis usually matches. However, in a heaving, pitching boat, car, or airplane, a serious mismatch can occur-causing heaving of another kind.
Selective Attention • Selective Attention (p.106): Voluntarily focusing on a specific sensory input. • Seat of the Pants Phenomenon: As you sit in class, receptors for touch and pressure in the seat of your pants are sending nerve impulses to your brain. Although these sensations have been present all along, you were probably not aware of them until just now. The “seat of the pants phenomenon” is an example of selective attention. • The cocktail party effect: Another example of selective attention. We are able to tune in on a single sensory message (conversation) while excluding others. If you are listening to one person intently, another person nearby can talk backward and you will not notice the strange speech! (Wood & Cowan, 1995)
Sensory Gating of Pain • One type of pain will sometimes cancel another (p.103) • Gate Control Theory suggests that pain messages from different nerve fibers pass through the same neural “gate” in the spinal cord. • If the gate is “closed” by one pain message, other messages may not be able to pass through. • Messages carried by large, fast nerve fibers seem to close the spinal pain gate directly. Doing so can prevent slower, “reminding system” pain from reaching the brain. • Pain clinics use this effect by applying a mild electrical current to the skin. Such stimulation, felt only as a mild tingling, can greatly reduce more agonizing pain. • Counterirritation (Coon, p.188): Using mild pain to block more intense or long lasting pain. This explains why some of the oldest pain control techniques work (applying ice packs, hot-water bottles, mustard packs, vibration, or massage to other parts of the body). Pinching yourself or digging nails into the flesh may help at the dentist. Focus attention on the pain you are creating, and increase its intensity anytime the dentist’s work becomes more painful. It works for many people, but not all.
Acupuncture • Some researchers believe that gate control theory explains the painkilling effects of acupuncture(the Chinese medical art of relieving pain and illness by inserting thin needles into the body). P.103. • Acupuncture has an interesting side effect not predicted by sensory gating. People given acupuncture often report feelings of light-headedness, relaxation, or euphoria. Why? • To combat pain, the brain causes the pituitary gland to release painkilling chemicals called endorphins. (Endo means “within”, orphin means “opiate”). P.103. • Chemically, endorphins are quite similar to morphine.
Pain & Beta-Endorphins • The painkilling effect of placebos (fake pills or injections) appears to be based on a rise in endorphin levels (p.26). • A release of endorphins also seems to underlie “runner’s high”, masochism, acupuncture, and the euphoria sometimes associated with childbirth and painful initiation rites. • In each case, pain and stress cause the release of endorphins. These in turn induce feelings of pleasure or euphoria similar to morphine intoxication. • The “high” often felt by long-distance runners serves as a good example of the endorphin effect. In one experiment, runners were tested for pain tolerance. After running 1 mile, each was tested again. In the second test, all could withstand pain about 70% longer than before. The runners were then given naloxone, a drug that blocks the effects of endorphins. Following another 1 mile run, the subjects were re-tested. This time they had lost their earlier protection from pain. • People who say they are “addicted” to running may be closer to the truth than they realize.