Chapter 4

Sensation and Perception

LECTURE OUTLINE

I. Sensation and Perception: Your Ticket of Admission to the World Outside.

A. Sensation: is the stimulation of sensory receptors and the transmission of sensory information to the central nervous system.

B. Perception: is an active process in which sensations are organized and interpreted to form an inner representation of the world.

C. Five Senses:

1. Vision.

2. Hearing.

3. Smell.

4. Taste.

5. Touch.

D. Concepts that apply to sensation include: absolute threshold, difference threshold, signal-detection theory, and sensory adaptation.

E. Absolute Threshold: So, Is It There or Not?

1. Fechner founded a discipline known as psychophysics which focuses on ways in which we translate physical events such as light and sounds into psychological experiences.

2. Absolute threshold: refers to the weakest amount of a stimulus that a person can distinguish from no stimulus at all 50% of the time. Examples include:

a. Vision: a candle flame viewed from about 30 miles on a clear, dark night.

b. Hearing: a watch ticking from about 20 feet away in a quiet room.

c. Taste: 1 teaspoon of sugar dissolved in 2 gallons of water.

d. Smell: about one drop of perfume diffused throughout a small house (1 part in 500 million).

e. Touch: the pressure of the wing of a fly falling on a cheek from a distance of about 0.4 inch.

F. Difference Threshold: Is It the Same or Is It Different?

1. Difference Threshold: is the minimum difference in magnitude of two stimuli required to tell them apart 50% of the time. Similar to the just noticeable difference (jnd).

2. Weber found that for:

a. Light the fraction is 1/60^th.

b. Weight the fraction is 1/53^rd.

c. Constant pitch the fraction is 1/333.

G. Signal-Detection Theory: Is Being Bright Enough?

1. Signal-detection theory considers the human aspects of sensation, and perception and also assumes that the relationship between a physical stimulus and a sensory response is not just mechanical. Other factors include:

a. Training (learning).

b. Motivation (desire to perceive).

c. Psychological states such as fatigue or alertness.

H. Feature Detectors in the Brain: Firing on Cue.

1. Feature detectors are brain cells that respond to different aspects of features of a scene (e.g. angles, vertical, horizontal).

I. Sensory Adaptation: Where Did It Go?

1. Sensory adaptation refers to the sensory process of adjustment.

a. Becoming more sensitive to stimulation is referred to as sensitization or positive adaptation.

b. Becoming less sensitive to stimulation is referred to as desensitization or negative adaptation.

Notes:__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

II. Vision: Letting the Sun Shine In.

A. More than half of our brain’s cerebral cortex is devoted to visual functions.

B. Light: How Dazzling?

1. All forms of electromagnetic energy moves in waves.

a. Visible light at about 400 billionths of a meter in length (violet) to 700 billionths of a meter (red).

b. Radio waves extend for miles.

c. Cosmic rays: wavelengths are only a few trillionths of an inch long.

2. Sir Isaac Newton discovered the prism that could break light into different colors. Colors of the spectrum include:

a. Red, orange, yellow, green, blue, indigo, violet.

b. (Roy G. Biv)

c. The wavelength of visible light determines the color or hue.

C. The Eye: The Better to See You With.

1. Light first passes through the transparent cornea.

2. The amount of light that is allowed to enter is controlled by the muscle called the iris (the colored part of the eye).

3. The actual opening in the iris is called the pupil.

4. The lens adjusts or accommodates to the image by changing its thickness. The thickness permits a clear image of the object to be projected onto the retina.

5. The retina consists of cells called photoreceptors that are sensitive to light (photosensitive). There are two types of photoreceptors: rods and cones.

a. The retina contains several layers of cells; the rods and cones, bipolar cells, and ganglion cells. All of these are neurons.

i. The rods and cones respond to light with chemical changes that create neural impulses that are picked up by the bipolar cells. These then activate the ganglion cells.

ii. The axons of the million or so ganglion cells in our retina ultimately converge to form the optic nerve.

iii. The optic nerve conducts sensory input to the brain where it is relayed to the visual area of the occipital lobe.

6. Rods and Cones.

a. About 125 million rods and 6.4 million cones are distributed across the retina.

i. Cones are most densely packed in a small spot at the center of the retina called the fovea.

ii. Visual acuity (sharpness and detail) is greatest at this spot.

iii. Rods are most dense just outside the fovea toward the periphery of the retina.

b. Rods allow us to see in black and white.

c. Cones provide color vision.

d. In contrast to visual acuity is the blind spot which is the part of the optic nerve which leaves the eye.

e. Visual acuity: sharpness of vision

i. Nearsighted: People who have to be unusually close to a distant object to discriminate its details.

ii. Farsighted: People who see distant objects clearly but have difficulty focusing on nearby objects.

f. When a person is in their late 30s to mid 40s the lenses start to grow brittle, making it more difficult to accommodate to, or focus on, objects. This condition is called presbyopia.

7. Light Adaptation.

a. Dark adaptation: the process of adjusting to lower lighting conditions.

b. Adaptation to brighter lighting takes place much more rapidly.

D. Color Vision: Creating an Inner World of Color.

1. The wavelength of light determines its color or hue.

2. The value of color is its degree of lightness or darkness.

3. Saturation refers to how intense a color appears.

4. Warm and Cool Colors.

a. Colors on the green-blue side of the color wheel are considered to be cool in temperature.

b. Colors on the yellow-red side are considered to be warm.

5. Complementary Colors.

a. The colors across from one another on the color wheel are complementary. These include:

i. Red-green.

ii. Blue-yellow.

iii. If the complementary colors are mixed they dissolve into gray.

iv. (remember we are mixing lights not pigments).

6. Afterimages.

a. Persistent sensations of color are followed by perception of the complimentary color when the first color is removed.

E. Theories of Color Vision.

1. Our ability to perceive color depends on the eye’s transmission of different messages to the brain when lights with different wavelengths stimulate the cones in the retina.

F. CONTROVERSY IN PSYCHOLOGY: What Happens In The Eye And In The Brain When Light With Different Wavelengths Stimulate The Retina?

1. Trichromatic Theory.

a. Young found that he could create any color from the visible spectrum by simply varying the intensities of three lights: red, green, and blue-violet.

b. Helmholtz suggested that the retina in the eye must have three different types of color photoreceptors or cones.

c. The trichromatic theory is known as the Young-Helmholtz theory.

2. Opponent-Process theory.

a. Hering proposed that there are three types of color receptors but they don’t respond just to red, green and blue-violet.

b. They are pairs including red-green; blue-yellow; and a type that perceives differences in brightness.

c. These pairs of receptors are what make afterimages possible.

3. Research suggests that each theory of color vision is partially correct.

a. The cones may be as Helmholtz claimed.

b. The transmission of the signals to the brain are as Hering proposed.

G. Color Blindness: What Kind of “Chromat” Are You?

1. If you can discriminate among the colors of the visible spectrum, you have normal color vision and are labeled a trichromat.

2. People who are totally colorblind are called monochromats.

3. Partial color blindness is a sex-linked trait that affects mostly males. Partially color-blind people are called dichromats as they can discriminate only among two colors-red and green or blue and yellow-and the colors derived from mixing these colors.

III. Visual Perception: How Perceptive?

A. Visual perception is the process by which we organize or make sense of the sensory impressions caused by the light that strikes our eyes.

1. Visual perception involves our knowledge, expectations, and motivations.

2. Visual perception is an active process through which we interpret the world around us.

3. Gestalt psychologists refer to closure as being the integration of disconnected pieces of information into a meaningful whole or the tendency to perceive a complete or whole figure even when there are gaps in the sensory input.

a. This reflects the principle of closure.

B. Perceptual Organization: Getting It Together.

1. Gestalt psychologists are interested in the way we integrate bits and pieces of sensory stimulation into meaningful wholes.

a. Wertheimer discovered many rules that we use to do this called the laws of perceptual organization.

2. Figure-Ground Perception.

a. When figure-ground relationships are ambiguous, or capable of being interpreted in various ways, our perceptions tend to be unstable, shifting back and forth.

b. Examples include the Rubin vase and the Necker Cube.

3. Other Gestalt Rules for Organization include proximity, similarity, continuity, and common fate.

a. Proximity: nearness.

b. Similarity: we perceive similar objects as belonging together.

c. Continuity: we perceive a series of points or a broken line as having unity.

d. Common Fate: elements seen as moving together are perceived as belonging together.

4. Top-Down Versus Bottom-Up Processing.

a. Top-Down processing: use the larger pattern to guide subordinate tasks.

b. Bottom-Up processing: begin with bits and pieces of information and become aware of the pattern formed only after you’ve worked on it awhile.

C. Perception of Motion-Life on the Move.

1. The visual perception of movement is based on change of position relative to other objects.

2. Psychologists have studied several types of apparent movement (illusions of movement). These include: autokinetic effect, stroboscopic motion, and the phi phenomenon.

a. The Autokinetic Effect is the tendency to perceive a stationary point of light as moving in a dark room.

b. Stoboscopic Motion is what makes motion pictures possible.

i. The illusion of movement is provided by the presentation of a rapid progression of images of stationary objects.

D. Depth Perception: How Far Is Far?

1. Monocular and binocular cues both help us perceive the depth of objects.

a. Monocular Cues: are cues that can be perceived by one eye. They include: perspective, relative size, clearness, interposition, shadows, and texture gradients.

b. Perspective: distances between far off objects appear to be smaller than equivalent distances between nearby objects.

c. Relative size: the fact that distant objects look smaller than nearby objects of the same size.

d. Clearness of an object: We sense more details of nearby objects.

e. Interposition: Nearby objects can block our view of more distant objects. Interposition is placing of one object in front of another.

f. Shadows: opaque objects block light and produce shadows giving us a relationship to the source of light.

g. Texture Gradient: close objects are perceived as having rougher textures.

h. Motion Parallax: the tendency of objects to seem to move backward or forward as a function of their distance.

2. Binocular Cues: include retinal disparity and convergence.

a. Retinal disparity: the difference between projected images (e.g. different angles).

i. Closer objects have greater retinal disparity.

b. Convergence: causes feelings of tension in the eye muscles and provides another binocular cue for depth.

E. Perceptual Constancies: Is a Door a Rectangle When It Is Partly Open?

1. Size constancy allows us to perceive objects to be the same size even when viewed from different distances.

a. Experiences teach us about perspective.

2. Color constancy is the tendency to perceive objects as retaining their color even though lighting conditions may alter their appearance.

3. Brightness constancy is similar to color constancy.

4. Shape constancy is the tendency to perceive objects as maintaining their shape, even if we look at them from different angles so that the shape of their image on the retina changes dramatically.

F. Visual Illusions: Is Seeing Believing?

1. Illusions often named after the people who devised them:

a. Hering-Helmholtz (horizontal lines with radiating lines)

b. Muller-Lyer (two lines, same length with arrowheads)

c. Ponzo (illustrates rule of constancy)

IV. Hearing: Making Sense of Sound.

A. Sound or auditory stimulation, travels through the air like waves.

1. The changes in air pressure are vibrations that approach your ears in waves.

a. The human ear is sensitive to sound waves with frequencies from 20 to 20,000 cycles per second.

B. Pitch and Loudness-All Sorts of Vibes.

1. Pitch and loudness are two psychological dimensions of sound.

a. The pitch of a sound is determined by its frequency, or the number of cycles per second as expressed in the unit hertz (Hz).

i. The greater the number of cycles per second the higher the pitch of the sound.

b. The loudness of a sound roughly corresponds to the height or amplitude of sound waves and is expressed in decibels (dB).

i. 25 dB is equivalent in loudness to a whisper at 5 feet.

ii. 30 dB is equivalent in loudness to what your librarian would like at your college library.

iii. 85-90 dB a person may experience hearing damage with prolonged exposure.

C. The Ear: The Better to Hear You With.

1. The ear has three parts: the outer ear, middle ear, and the inner ear.

2. The outer ear is shaped to funnel sound waves to the eardrum.

a. The eardrum is a thin membrane that vibrates in response to sound waves and thereby transmits them to the middle and inner ears.

3. The middle ear contains the eardrum and three small bones: the hammer, the anvil, and the stirrup. The middle ear functions as an amplifier.

a. The stirrup is attached to another vibrating membrane the oval window. The oval window transmits vibrations into the inner ear to a bony tube called the cochlea.

b. The cochlea is a snail shaped structure that contains longitudinal membranes that divide in into three fluid filled chambers. One of the membranes that lies within the cochlea is the basilar membrane.

c. Attached to the basilar membrane is the organ of Corti sometimes referred to as the command post of hearing. Here there are 25,000 receptor cells called hair cells.

d. Hair cells dance in response to the vibrations of the basilar membrane. Their up and down movements generate neural impulses which are transmitted to the brain via the auditory nerve.

e. Auditory input is then projected onto the hearing areas of the temporal lobes of the cerebral cortex.

D. Locating Sounds-Up, Down, and Around.

1. A sound that is louder in the right ear is perceived as coming from the right.

2. Both loudness and the sequence in which the sounds reach the ears provide directional cues.

E. Perception of Loudness and Pitch.

1. The loudness and pitch of sounds appear to be related to the number of receptor neurons on the organ of Corti that fire and how often they fire.

2. Psychologists generally agree that sounds are perceived as louder when more of these sensory neurons fire.

F. CONTROVERSY IN PSYCHOLOGY: How Do We Explain Pitch Perception? What Happens When the Basilar Membrane Runs Out of Places to Vibrate? What Happens When It Cannot Vibrate Fast Enough?

1. Place theory: holds that the pitch of a sound is sensed according to the place along the basilar membrane that vibrates in response to it.

2. Frequency theory: notes that for us to perceive lower pitches, we need the stimulation of neural impulses that match the frequency of the sound waves.

G. Deafness: Navigating a World of Silence.

1. More than 1 in 10 Americans has a hearing impairment, and 1 in 100 cannot hear at all.

2. Two major types of deafness are conductive and sensorineural deafness.

a. Conductive deafness: stems from damage to the structures of the middle ear.

i. This is the hearing impairment often found among older people.

b. Sensorineural deafness usually stems from damage to the structures of the inner ear, most often the loss of hair cells, which normally do not regenerate.

i. Acoustic trauma: prolonged exposure to very loud noises.

ii. The ringing sensation that often follows exposure to loud noises probably means that hair cells have been damaged.

V. Chemical Senses: Smell and Taste.

A. Smell and taste are chemical senses.

B. Smell: Sampling Molecules in the Air.

1. If you did not have a sense of smell an onion and an apple would taste the same to you.

2. Humans can detect the odor of 1 one-millionth of a milligram of vanilla in a liter of air.

3. An odor is a sample of molecules of the substance being sensed.

a. Odors are detected by sites on receptor neurons in the olfactory membrane high in each nostril.

b. Their firing transmits information about odors to the brain via the olfactory nerve.

4. The sense of smell adapts rapidly to odors such that we lose awareness of them.

C. Taste: Yes, You’ve Got Taste.

1. Dogs can perceive the taste quality of sweetness as can pigs, but cats cannot.

2. There are four primary taste qualities: sweet, sour, salty, and bitter.

a. Some argue for a fifth termed umami, which means meaty or savory.

3. The flavor of food depends on its odor, texture, and temperature as well as on its taste.

4. Taste is sensed through taste cells, receptor neurons located on taste buds.

a. Humans have approximately 10,000 taste buds most of which are located on the edge and back of your tongue.

i. Catfish can detect food through murky water and across long distances because their bodies are studded with nearly 150,000 taste buds.

b. Sensitivities to different tastes apparently have a strong genetic component.

c. Taste cells reproduce rapidly enough to completely renew themselves about once a week.

d. Because the flavor of food represents both its taste and its odor, older people experience loss in the flavor on their food, not taste.

VI. The Skin Senses (Yes, It Does).

A. The skin senses include touch, pressure, warmth, cold, and pain.

B. Touch and Pressure: Making Contact.

1. Active touching involves reception of information concerning not only touch per se but also pressure, temperature, and feedback from the muscles involved in movements of our hands.

2. Psychophysicists use methods such as the two-point threshold to assess sensitivity to pressure.

a. Sensory nerve endings are more densely packed in the fingertips and face than in other locations.

b. The sense of pressure, like the sense of touch undergoes rapid adaptation.

C. Temperature: Sometimes Everything Is Relative.

1. The receptors for temperature are neurons located just beneath the skin.

a. Sensations of temperatures are relative.

D. Pain: Too Much of a Good Thing?

1. A Gallup survey of 2,002 adults in the U.S. showed that 89% experience pain at least once a month.

a. 55% of people over age 65 say they experience pain daily

b. 43% of Americans say that pain curtails their activities

c. 50% say that pain puts them in a bad mood

2. Pain means that something is wrong in the body.

a. Pain results when neurons called nociceptors in the skin are stimulated

b. Pain is adaptive.

c. There are no nerve endings for pain in the brain.

d. Postaglandins (substance P) facilitate transmission of the pain message to the brain and heighten circulation to the injured area.

i. Inflammation serves the biological function of attracting infection-fighting blood cells to the affected area to protect it against invading germs.

ii. The pain message is relayed from the spinal cord to the thalamus and then projected to the cerebral cortex.

e. Other aspects influence pain:

i. Visual and other sensory inputs tell us what is happening and influence the cognitive interpretation of the situation.

3. Phantom Limb Pain.

a. About 2 out of 3 combat veterans with amputated limbs report feeling pain in missing or phantom limbs.

i. Seems to involve activation of nerves in the stump of the missing limb.

4. Gate Theory.

a. Melzack originated the gate theory of pain.

i. The nervous system can process only a limited amount of stimulation at a time.

ii. In a sense, there is competition for the attention of neurons.

5. Acupuncture.

a. Research has shown that acupuncture stimulates nerves that reach the hypothalamus and may also result in the release of endorphins.

E. LIFE CONNECTIONS: Pain, Pain, Go Away-Don’t Come Again Another Day

1. The primary treatment has been chemical; pain killing drugs.

2. Accurate Information: giving people accurate information and thorough information about their condition often helps them manage pain.

a. Knowledge of medical procedures reduces stress by helping people maintain control over their situation.

3. Distraction and Fantasy: The Nintendo Approach to Coping With Pain?

a. Diverting attention from pain helps many people cope with it.

4. Hypnosis has been used to reduce chronic pain, as an anesthetic in dentistry, childbirth, even in some forms of surgery.

a. Hypnosis can also aid in the use of distraction and fantasy.

5. Relaxation Training.

a. Tensing muscles is uncomfortable in itself, arouses the sympathetic nervous system, and focuses our attention on the pain.

b. Some psychological methods of relaxation focus on relaxing muscle groups, breathing exercises, and using relaxing imagery.

c. Biofeedback is also used to help people relax targeted muscle groups.

i. Relaxation training with biofeedback seems to be at least as effective as most medications for migraine headaches.

ii. Also effect for helping chronic pain in the lower back and jaw.

6. Coping with Irrational Beliefs.

a. Some patients may be unwilling to allow themselves to be distracted from pain and discomfort. Cognitive methods aimed at changing irrational beliefs hold some promise.

7. Other methods.

a. One is a sense of commitment. It might be helpful to recall that we chose to participate rather than see ourselves as helpless victims. This gives a sense of control of the situation.

b. Supportive social networks help as well.

VII. Kinesthesis and the Vestibular Sense.

A. Kinesthesis: How Moving?

1. Kinesthesis is the sense that informs you about the position and motion of parts of the body.

a. Sensory information is fed back to the brain from sensory organs in the joints, tendons, and muscles.

B. The Vestibular Sense: How Upright?

1. Your vestibular sense tells you whether you are upright.

a. Sensory organs located in the semicircular canals and elsewhere in the ears monitor your body’s motion and position in relation to gravity.

i. They tell you if you are falling and if your body is changing speed.

VIII. Virtual Reality and ESP: Sensation and Perception on the Edge

A. Sensation, Perception, and Virtual Reality.

1. Virtual Reality: is the perception of events that are fed directly into the senses via electronic technology.

a. Virtual Rooms

b. Cybersex or virtual sex

B. Extrasensory Perception: Is There Perception Without Sensation?

1. 60% of Americans believe that some people have psychic powers or ESP.

2. Precognition, Psychokinesis, Telepathy, and Clairvoyance.

a. Precognition: able to perceive future events in advance.

b. Psychokinesis: mentally manipulating or moving objects.

c. Telepathy: direct transmission of thoughts or ideas from one person to another.

d. Clairvoyance: the perception of objects that do not stimulate the sensory organs.

e. Psi communication refers to the perception of objects or events through means other than sensory organs.

f. Rhine studied ESP for several decades with the conclusion that some people might have some degree of ESP.

g. Ganzfeld Procedure: one person acts as the “sender” and the other as the “receiver”. Receivers correctly identified the visual stimulus 38% of the time, a percentage unlikely to be due to chance.

h. File drawer problem: ESP researchers are less likely to report research results that show failure.

3. People who have demonstrated ESP with one researcher have failed to do so with another researcher. Not one person has emerged who can reliably show psi communication from one occasion to another and from one researcher to another.

IX. FEATURES: A CLOSER LOOK: Advances in Science? The Case of the Aromatic T-shirts.

A. Men wore shirts for two days without deodorant, eating spicy foods, pets, and sex.

B. Women were then asked to smell the shirts. By and large the shirts selected as favorites had been worn by men who were similar in genetic makeup to the women’s father.

X. A Closer Look: How Did the Animals Know the Tsunami Was Coming?

A. Tsunami that hit the southern coast of south central Asia

1. One quarter of a million people were killed

2. People were caught off guard but the animals were not

a. Elephants began to trumpet

b. Dogs refused to go outdoors

c. Flamingoes abandoned their sanctuary in the low lying areas

3. Animals seem to be able to detect subtle changes in the environment

a. Supersensitive to sounds, temperature, touch, vibration

Back to Main Page