Chapter 4Sensation and Reality

Psychophysics

• Study of relationship between physical stimuli and sensations they evoke in a human observer

• Absolute threshold: Minimum amount of physical energy necessary to produce a sensation

• Subliminal perception: Perception of a stimulus below the threshold for conscious recognition

• Difference threshold: A change in stimulus intensity that is detectable to an observer

Just Noticeable Difference (JND)

• Any noticeable difference in a stimulus

Weber’s Law

• The amount of change needed to produce a constant JND is a constant proportion of the original stimulus intensity

General Properties of Sensory Systems

• Perceptual features: Basic stimulus patterns• Sensory coding: Converting important

features of the world into messages understood by the brain

Sensation and Perception

• Sensation: Information arriving from sense organs (eye, ear, etc.)

• Perception: Mental process of organizing sensations into meaningful patterns

p. 120

Vision: The Key Sense

• Visible spectrum: Narrow spread of the electromagnetic spectrum to which the eyes respond

Parts of the Eye

• Lens: Structure in the eye that focuses light rays

• Photoreceptors: Light-sensitive cells in the eye

More Parts of the Eye

• Retina: Light-sensitive layer of cells in the back of the eye– Easily damaged from excessive exposure

to light (staring at an eclipse) • Cornea: Transparent membrane covering the

front of the eye; bends light rays inward

Accommodation

• Changes in the shape of the lens of the eye

Fig. 4-3, p. 123

Fig. 4-1, p. 122

Fig. 4-4, p. 124

Video: Anatomy of the Eye: Virtual Reality

After clicking ‘Play Video’ use your mouse to manipulate this active figure.

Vision Problems

• Hyperopia: Difficulty focusing nearby objects (farsightedness)

• Myopia: Difficulty focusing distant objects (nearsightedness)

• Astigmatism: Corneal, or lens defect that causes some areas of vision to be out of focus; relatively common

• Presbyopia: Farsightedness caused by aging

Fig. 4-5, p. 124

Light Control

• Iris: Colored circular muscle that controls amount of light entering the eye

• Pupil: Opening at the front of the eye through which light passes

Light Vision

• Cones: Visual receptors for colors and bright light (daylight); 5 million in each eye

• Rods: Visual receptors for dim light; only produce black and white; about 120 million total

• Blind spot: Area of the retina lacking visual receptors

Fig. 4-6, p. 125

Fig. 4-7, p. 125

Fig. 4-8, p. 126

More on Light Control

• Visual acuity: Sharpness of visual perception• Fovea: Area at the center of the retina

containing only cones (50,000)• Peripheral vision: Vision at edges of visual

field; side vision – Many superstar athletes have excellent

peripheral vision• Tunnel vision: Loss of peripheral vision

Fig. 4-9, p. 126

Fig. 4-11, p. 127

Video: Transmission of Light through the Eye

Color Vision

Trichromatic Theory

• Color vision theory that states we have three cone types: red, green, blue– Other colors produced by a combination of

these

Opponent Process Theory

• Color vision theory based on three “systems”: red or green, blue or yellow, black or white– Exciting one color in a pair (red) blocks the

excitation in the other member of the pair (green)

– Afterimage: Visual sensation that remains after stimulus is removed (seeing flashbulb after the picture has been taken)

Fig. 4-12, p. 128

Fig. 4-13, p. 128

Simultaneous Color Contrast

• Changes in perceived hue that occur when a colored stimulus is displayed on backgrounds of various colors

Color Blindness

• Color blindness: Inability to perceive colors; lacks cones or has malfunctioning cones– Total color blindness is rare

• Color weakness: Inability to distinguish some colors– Red-green is most common; much more

common among men than women– Recessive, sex-linked trait on X

chromosome

Ishihara Test

• Test for color blindness and color weakness

Fig. 4-16a, p. 129

Fig. 4-16b, p. 129

Fig. 4-16c, p. 129

Fig. 4-17, p. 130

Dark Adaptation

• Increased retinal sensitivity to light after entering the dark; similar to going from daylight into a dark movie theater

• Rhodopsin: Light-sensitive pigment in the rods; involved with night vision

• Night blindness: Blindness under low-light conditions; hazardous for driving at night

Fig. 4-18, p. 131

Hearing

• Sound waves: Rhythmic movement of air molecules

• Pitch: Higher or lower tone of a sound• Loudness: Sound intensity

Fig. 4-19, p. 132

Hearing: Parts of the Ear

• Pinna: Visible, external part of the ear• Tympanic membrane: Eardrum• Auditory ossicles: Three small bones that

vibrate; link eardrum with the cochlea– Malleus (hammer)– Incus (anvil)– Stapes (stirrup)

Fig. 4-20, p. 133

Hearing: Parts of the Ear (cont)

• Cochlea: Snail-shaped organ that makes up inner ear

• Hair cells: Receptor cells within cochlea that transduce vibrations into nerve impulses

Fig. 4-21, p. 134

Fig. 4-22, p. 134

How Do We Detect Higher and Lower Sounds?

• Frequency theory: As pitch rises, nerve impulses of a corresponding frequency are fed into the auditory nerve

• Place theory: Higher and lower tones excite specific areas of the cochlea

Conduction Hearing Loss

• Poor transfer of sounds from tympanic membrane to inner ear– Compensate with amplifier (hearing aid)

Sensorineural Hearing Loss

• Caused by damage to hair cells or auditory nerve– Hearing aids little or no help in these cases– Cochlear implant: Electronic device that

stimulates auditory nerves directly

Fig. 4-24, p. 135

Noise-Induced Hearing Loss

• Damage caused by exposing hair cells to excessively loud sounds– Typical at rock concerts– By age 65, more than 40% of hair cells are

gone

Fig. 4-23, p. 134

Fig. 4-25, p. 135

Smell

• Olfaction: Sense of smell• Dysosmia: Loss or impairment of sense of

smell• Lock-and-key theory: Odors are related to

shapes of chemicals and molecules• Pheromones: Airborne chemical signal

– Vomeronasal organ: Sense organ for pheromones

Gustation

• Sense of taste– Four taste sensations: sweet, salt, sour,

bitter – Most sensitive to bitter, less to sour, less to

salt, least sensitive to sweet– Umami: Possible fifth taste sensation;

brothy taste

Taste Buds

• Taste-receptor cells

Fig. 4-26, p. 136

Fig. 4-27, p. 138

Somesthetic Senses

• Sensations produced by skin, muscles, joints, viscera, and organs of balance

• Skin senses (touch): Light touch, pressure, pain, cold, warmth

• Kinesthetic: Detect body position and movement• Vestibular: Balance, acceleration, and position in

space

Skin Receptors

• Sensory organs for touch, pressure, pain, cold, and warmth

Pain

• Visceral pain: Pain originating in internal organs

• Referred pain: Pain felt in one part of the body, but coming from another

• Somatic pain: Sharp, bright, fast; comes from skin, joints, muscles, tendons

Types of Pain

• Warning system: Pain carried by large nerve fibers; sharp, bright, fast pain that tells you body damage may be occurring (e.g., knife cut)

• Reminding system: Small nerve fibers; slower, nagging, aching, widespread; gets worse if stimulus is repeated; reminds brain that body has been injured

Dynamic Touch

• Touch experienced when the body is in motion; a combination of sensations from skin receptors, muscles, and joints

Fig. 4-29, p. 140

Vestibular System

• Otolith organs: Sensitive to movement, acceleration, and gravity

• Semicircular canals: Fluid-filled tubes in ears that are sensory organs for balance

• Crista: “Float” that detects movement in semicircular canals

• Ampulla: A wider part of the canal

Fig. 4-30, p. 140

Fig. 4-31, p. 141

Vestibular System and Motion Sickness

• Motion sickness is directly related to vestibular system

Sensory Conflict Theory

• Motion sickness results from a mismatch between information from vision, vestibular system, and kinesthesis– After spinning and stopping, fluid in

semicircular canals is still spinning, but head is not

– Mismatch leads to sickness• Medications, relaxation, and lying down might

help

Adaptation, Attention, and Sensory Gating

• Sensory adaptation: When sensory receptors respond less to unchanging stimuli

• Selective attention: Voluntarily focusing on a specific sensory input

• Sensory gating: Facilitating or blocking sensory messages in the spinal cord

Gate Control Theory of Pain

• Gate control theory: Pain messages from different nerve fibers pass through the same “neural” gate in the spinal cord.– If gate is closed by one pain message,

other messages may not be able to pass through

Fig. 4-33, p. 143

Beta-endorphin

• Natural pain-killing brain chemical similar to morphine

Phantom Limb

• Missing limb feels like it is present, like always, before amputation or accident

Controlling Pain

• Fear, or high levels of anxiety, almost always increase pain

• If you can regulate a painful stimulus, you have control over it

• Distraction can also significantly reduce pain• The interpretation you give a stimulus also

affects pain

Coping With Pain

• Prepared childbirth training: Promotes birth with a minimal amount of drugs or painkillers

• Counterirritation: Using mild pain to block more intense or long-lasting pain