Our Sensational Senses

Definitions

1. Sensation - the detection of physical energy emitted or reflected by physical objects

2. Perception - processes that organize sensory impulses into meaningful patterns

3. Introduction to the senses

   a. There are five widely known senses and other lesser known senses

   b. All senses evolved to help us survive

The riddle of separate sensations

1. Sense receptors stimulate sensory neurons which stimulate brain cells

2. Encoding the electrical messages - the nervous system uses two kinds of codes

   a. Anatomical codes

   • (1) Doctrine of specific nerve energies - signals received by the sense organs stimulate different nerve pathways, which terminate in different areas of the brain

   • (2) Does not fully explain separate sensations; different skin senses do not have distinct nerve pathways; different colors do not have distinct pathways

   b. Functional codes

   • (1) Particular receptors fire or are inhibited in the presence of certain stimuli

   • (2) Codes relate to which cells, how many, and the rate and pattern of firing

3. Synesthesia occurs when stimulation of one sense evokes sensations in another

Measuring the senses

1. Psychophysics - how the physical properties of stimuli are related to our psychological experience of them

2. Absolute threshold - the smallest amount of energy a person can detect reliably (50 percent of the time)

3. Difference threshold - the smallest difference in stimulation that a person can detect reliably (50 percent of the time); also called just noticeable difference (jnd)

4. Signal detection theory

   a. Accounts for response bias (tendency to say yes or no to a signal)

   b. Separates sensory processes (the intensity of the stimulus) from the decision process (influenced by observer’s response bias)

Sensory Adaptation

1. Decline in sensory responsiveness occurs when a stimulus is unchanging; nerve cells temporarily stop responding

2. Sensory deprivation studies

   a. Early deprivation study subjects became edgy, disoriented, confused, restless and had hallucinations

   b. Early studies exaggerated negative reactions

3. Brain requires minimum stimulation to function normally

Sensing without perceiving

1. “Cocktail party phenomenon” - we routinely block out unimportant sensations

2. Selective attention protects us from being overwhelmed with sensations

Vision

A. What we see

1. Stimulus for vision is light, which travels in waves

2. Characteristics of light waves

   a. Hue - color that is related to wavelength

   b. Brightness - intensity, corresponds to amplitude of the wave

   c. Saturation - colorfulness and complexity of the range of wavelengths

3. Psychological dimensions of visual experience are hue, brightness, saturation

4. Physical properties of light are wavelength, intensity, complexity

B. An eye on the world

1. Cornea - front part of the eye; protects the eye and bends light rays toward lens

2. Lens - located behind the cornea; focuses light by changing curvature

3. Iris - muscles that control the amount of light that gets into the eye

4. Pupil - round opening surrounded by iris; widens and dilates to let light in

5. Retina - located in the back of the eye, contains visual receptors

   a. Parts of retina

   • (1) Two types of receptors

     • (a) Rods - sensitive to light, not to color

     • (b) Cones - see color, but need more light to respond

   • (2) Fovea - center of retina, sharpest vision, contains only cones

     b. Processing visual information

   • (1) Dark adaptation - time it takes to adjust to dim illumination; reflects mainly increase in sensitivity of rods

   • (2) Rods and cones connect to bipolar neurons that connect to ganglion cells, whose axons converge to form optic nerve, that carries information out of the eye to the brain

   • (3) Optic nerve - leaves the eye at optic disc; no rods or cones; blind spot on retina

C. Why the visual system is not a camera

1. Eyes are not a passive recorder of external world; neurons build picture of the external world by detecting its meaningful features

2. Special feature detector cells in visual cortex code complex features

3. Other cells in the visual system respond maximally to certain specific visual information like faces, bull’s‐eyes, or starlike shapes

4. Frequency, pattern, and rhythm of firing all provide information to the brain

D. How we see colors

1. Trichromatic (Young‐Helmholtz) theory a. This approach applies to the first level of processing (in the retina)

   b. Retina contains three types of cones: one responds to blue, another to green, another to red; these combine to make all colors c. People with color deficiencies lack particular types of cones

2. Opponent‐process theory

   a. Second stage of color processing in the ganglion cells of the retina and neurons in the thalamus and visual cortex (opponent process cells)

   b. They turn off to one wavelength in a pair and on to the other

   c. Another opponent‐process system responds in opposing fashion to black and white, providing information about brightness

   d. Opponent‐process theory can explain why we see negative afterimages

3. Perceived color of an object also depends on the wavelengths reflected by the other objects around it

E. Constructing the visual world

1. Visual perception - the mind interprets the retinal image and constructs the world using information from other senses

2. Form perception a. Gestalt psychologists studied how people organize the visual world into meaningful patterns b. Strategies for building perceptual units include use of: figure/ground distinction, proximity, closure, similarity, and continuity

3. Depth and distance perception - object’s location inferred from distance or depth cues

   a. Binocular cues - dependent on information from both eyes

   (1) Changes in angle of convergence of the image seen by each eye provide distance cues

   (2) Retinal disparity - disparity in the lateral separation between two objects as seen by the two eyes is used to infer depth or distance

   b. Monocular cues ‐ cues that do not depend on using both eyes include interposition and linear perspective

4. Visual constancies: When seeing is believing

   a. Perceptual constancy - our perception of objects is unchanging though the sensory patterns they produce are constantly shifting

   b. Visual constancies ‐ shape, location, size, brightness, and color

5. Visual illusions - When seeing is misleading; visual constancies may occasionally fool us, resulting in visual illusions

Hearing

A. What we hear

1. Stimulus for sound is a wave of pressure created when an object vibrates; that causes molecules in a transmitting substance (such as air) to move

2. Characteristics of sound waves

   a. Loudness - intensity of a wave’s pressure; corresponds to amplitude; also affected by

pitch; units of measure are decibels

b. Pitch - frequency (and intensity) of wave; units of measure are hertz (cycles per second) c. Timbre ‐ complexity of wave; the distinguishing quality of a sound

3. When all frequencies of the sound spectrum are present, white noise occurs

B. An ear on the world

1. Sound wave passes into the outer ear through a canal to strike the eardrum

2. Eardrum vibrates at the same frequency and amplitude as the wave

3. The wave vibrates three small bones in the inner ear - the hammer, anvil, and stirrups; intensify the sound; the third bone pushes on a membrane that guards the entrance to the inner ear, of which the cochlea is a part

4. The cochlea contains the receptor cells called cilia, or hair cells, that are embedded in the basilar membrane stretching across the cochlea

5. Pressure causes movement in the basilar membrane; the hair cells initiate a signal to the auditory nerve, which carries the message to the brain

6. The pattern of movement of the basilar membrane influences the pattern and frequency of how the neurons fire, which determines what is heard

C. Constructing the auditory world

1. Perception is used to organize patterns of sounds to construct meaning

2. Strategies used to organize and interpret sounds include the Gestalt principles of figure/ground, proximity, continuity, similarity, closure

3. Loudness is a distance cue

4. Differences in loudness and/or time of arrival of auditory stimuli to the two ears allows us to estimate direction

Other Senses

A. Taste

1. Chemicals stimulate receptors (inside taste buds) on tongue, throat, and roof of mouth

   a. Papillae - bumps on tongue, contain taste buds

   b. Taste receptors are replaced every 10 days; number of taste buds and receptor cells declines with age

Four basic tastes: salty, sour, bitter, sweet

a. Each taste produced by a different type of chemical

b. Each can be perceived wherever there are receptors

c. Flavors are a combination of the four, but unclear how this occurs

d. Natural tastes - preference for sweet

e. Taste is influenced by smell, culture, individual differences, temperature, texture

f. There are genetic differences in sensitivity to certain tastes

B. Smell

1. The sense of smell is called olfaction

2. Receptors are millions of specialized neurons embedded in a mucous membrane in upper part of nasal passage; respond to chemical molecules in the air

3. Signals travel from receptors to olfactory bulb in the brain

4. Not well understood/no agreement on which smells are basic; there may be a thousand different receptor types

5. Sense of smell allows us to sniff out danger such as smoke, spoiled food, poison gases

6. Odor preferences influenced by culture, context, and experience

C. Senses of the skin

1. Skin protects innards, helps identify objects, involved in intimacy, serves as boundary

2. Skin senses include: touch (pressure), warmth, cold, and pain

   a. No correspondence between four sensations and types of receptors, except for pressure

   b. Many aspects of touch continue to baffle scientists

D. The mystery of pain

1. Pain differs from the other skin senses in that removal of stimulus doesn’t always terminate sensation

   1. Chronic pain puts stress on the body

   2. Gate‐control theory of pain a. To experience pain sensation, impulses must pass a “gate” to central nervous system b. The gate is made of neurons that either transmit or block pain message c. Chronic pain results when fibers that close the gate are damaged

The neuromatrix theory of pain

a. Gate‐control theory can't explain phantom pain

(1) The brain can generate pain without external stimulation

(2) The neuromatrix gives us a sense of our own bodies

(3) Abnormal activity can occur in the neuromatrix as a result of memories and expectations

E. The environment within

1. Kinesthesis - tells us about location and movement of body parts using pain and pressure receptors in muscles, joints, and tendons

2. Equilibrium ‐ gives information about position and motion of the body as a whole using three semicircular canals in the inner ear

Perceptual Powers : Origins and Influences

A. Inborn abilities and perceptual lessons

1. Studies with animals show that experience during a critical period may ensure survival of skills present at birth

2. Research concludes that infants are born with many perceptual abilities

   a. Ability to detect edges, angles, sizes, and colors

   b. Visual cliff experiment shows depth perception by two months of age

   c. Taste and smell preferences, ability to discriminate odors, distinguish voices from

   other sounds, localize sound is present early

B. Psychological and cultural influences on perception

1. Needs, beliefs, emotions, expectations (perceptual set) influence perception

2. Culture affects perception by shaping stereotypes and directing attention

Puzzles of Perception

A. Subliminal perception

1. Evidence exists for perceptual processing without awareness

2. A visual stimulus of which one is not aware can influence responses

3. Evidence for influence of nonconscious processes in memory, thinking, decision making

4. Subliminal perception is the perception of stimuli that are presented at below‐threshold levels

5. Subliminal stimuli can affect responses to simple stimuli, but there is no empirical evidence of subliminal persuasion

B. Extrasensory perception : Reality or illusion?

1. Reported ESP experiences include telepathy and precognition

2. Evidence or coincidence?

   a. Most “evidence” for ESP comes from unreliable anecdotal accounts

   b. Parapsychology - field concerned with the study of ESP

   c. Studies under controlled conditions by parapsychologists

   (1) Some positive results found but there were methodological problems and results have not been replicated

   (2) There is presently no empirical evidence to support the existence of any of the phenomena included in the definition of ESP

3. Magicians' trick us by relying on the tendency of the mind to impose its own interpretation on perceptions