Module 5

Sensation

THREE DEFINITONS

• Eyes, ears, nose, skin, and tongue are complex, miniaturized, living sense organs that automatically gather information about your environment

• Transduction– Process in which a sense organ changes, or

transforms, physical energy into electrical signals that become neural impulses, which may be sent to the brain for processing

• Adaptation– The decreasing response of the sense organs as

they’re exposed to a continuous level of stimulation

THREE DEFINITONS (CONT’D)

• Sensation versus perception– Relatively meaningless bits of information that result

when the brain processes electrical signals that come from the sense organs

• Perceptions– Meaningful sensory experiences that result after the

brain combines hundreds of sensations

Cocktail-party phenomenon

• The cocktail party effect describes the ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations.

• Form of selective attention.

Energy v. Chemical senses

Energy Senses Chemical Senses

Vision• Our most

dominating sense.• Visual Capture

EYE: VISION (CONT’D)

EYE: VISION (CONT’D)

• Structure and function

– Eyes perform two separate processes• first: gather and focus light into precise area in the

back of eye• second: area absorbs and transforms light waves

into electrical impulses

– Process called transduction

Phase Two: Getting the light in the eye

EYE: VISION (CONT’D)

• Retina

– Three layers of cells• back layer contains two kinds of photoreceptors

that begin the process of transduction• change light waves into electrical signals• rod located primarily in the periphery• cone located primarily in the center of the retina

called the fovea

EYE: VISION (CONT’D)

• Rods

– Photoreceptor that contain a single chemical, called rhodopsin

– Activated by small amounts of light– Very light sensitive– Allow us to see in dim light– See only black, white, and shades of gray

EYE: VISION (CONT’D)

• Cones

– Photoreceptors that contain three chemicals called opsins

– Activated in bright light– Allow us to see color– Cones are wired individually to neighboring cells– Allow us to see fine detail

Transduction Continued

• Order is Rods/Cones to Bipolar to Ganglion to Optic Nerve.

• Sends info to thalamus- area called lateral geniculate nucleus (LGN).

• Then sent to cerebral cortexes.

• Where the optic nerves cross is called the optic chiasm.

EYE: VISION (CONT’D)

• Making colors from wavelengths– Sunlight is called white light because it contains all

the light waves– White light passes through a prism; separates light

waves that vary in length– Visual system transforms light waves of various

lengths into millions of different colors– Shorter wavelengths of violet, blue, green– Longer wavelengths of yellow, orange, and red– An apple is seen as red because reflection of longer

light waves that brain interprets as red

EYE: VISION (CONT’D)

Trichromatic Theory

Three types of cones:• Red• Blue• Green• These three types of

cones can make millions of combinations of colors.

• Does not explain afterimages or color blindness well.

Opponent-Process theory

The sensory receptors come in pairs.

• Red/Green• Yellow/Blue• Black/White• If one color is

stimulated, the other is inhibited.

Afterimage

EYE: VISION (CONT’D)

• Color blindness– Inability to distinguish two or more shades in the color

spectrum– Monochromatic

• total color blindness; black and white• result of only rods and one kind of functioning cone

– Dichromatic• inherited genetic defect; mostly in males• trouble distinguishing red from green• two kinds of cones• see mostly shades of green

Hearing

Our auditory sense

The Ear

EAR: AUDITION

• Stimulus– Sound waves

• stimuli for hearing (audition)• ripples of different sizes; sound waves travel

through space with varying heights and frequency– Height

• distance from the bottom to the top of a sound wave; amplitude

– Frequency • number of sound waves occurring within a second

EAR: AUDITION (CONT’D)

• Loudness– Subjective experience of a sound’s intensity– Brain calculates loudness from specific physical

energy (amplitude of sound waves)

• Pitch– Subjective experience of a sound being high or low– Brain calculates from specific physical stimuli– Speed or frequency of sound waves– Measured in cycles (how many sound waves in a

second)

EAR: AUDITION (CONT’D)

• Measuring sound waves

– Decibel: unit to measure loudness

– Threshold for hearing• 0 decibels (no sound)• 140 decibels (pain and permanent hearing loss)

EAR: AUDITION (CONT’D)

EAR: AUDITION (CONT’D)

• Outer, middle, and inner ear

– Outer ear• consists of three structures

– external ear– auditory canal– tympanic membrane

EAR: AUDITION (CONT’D)

• Outer, middle, and inner ear

– Outer ear• external ear

– oval-shaped structure that protrudes from the side of the head

• function– pick up sound waves and then send them down

the auditory canal

EAR: AUDITION (CONT’D)

• Outer, middle, and inner ear

– Outer ear• auditory canal

– long tube that funnels sound waves down its length so that the waves strike the tympanic membrane (ear drum)

EAR: AUDITION (CONT’D)

• Outer, middle, and inner ear

– Outer ear• tympanic membrane

– taut, thin structure commonly called the eardrum

– sound waves strike the tympanic membrane and cause it to vibrate

EAR: AUDITION (CONT’D)

• Outer, middle, and inner ear

– Middle ear• bony cavity sealed at each end by membranes that

are connected by three tiny bones called ossicles• hammer, anvil, and stirrup

– hammer is attached to the back of the tympanic membrane

– anvil receives vibrations from the hammer– stirrup makes the connection to the oval

window (end membrane)

EAR: AUDITION (CONT’D)

• Outer, middle, and inner ear

– Inner ear• contains two structures sealed by bone

– cochlea: involved in hearing– vestibular system: involved in balance

EAR: AUDITION (CONT’D)

• Cochlea

– Bony coiled exterior that resembles a snail’s shell

– Contains receptors for hearing

– Function is transduction

– Transforms vibrations into nerve impulses sent to the brain for processing into auditory information

EAR: AUDITION (CONT’D)

EAR: AUDITION (CONT’D)

• Auditory cues– Direction of sound

• determined by brain; calculates slight difference in time it takes sound waves to reach the two ears

– Calculating pitch• frequency theory

– applies only to low-pitched sounds– rate ate that nerve impulses reach the brain

determines how low a sound’s pitch is• place theory

– brain determines medium-to-higher-pitched sounds from the place on the basilar membrane where maximum vibration occurs

EAR: AUDITION (CONT’D)

• Auditory cues

– Calculating loudness• brain calculates loudness primarily from the

frequency or rate of how fast or how slow nerve impulses arrive from the auditory nerve

Vestibular Sense

• Tells us where our body is oriented in space.

• Our sense of balance.

• Located in our semicircular canals in our ears.

VESTIBULAR SYSTEM: BALANCE (CONT’D)• Motion sickness (sensory mismatch between information

from the vestibular system)– symptoms: feelings of discomfort, nausea, and

dizziness in a moving vehicle– head bouncing, but distant objects look fairly steady

• Meniere’s disease (malfunction of the semicircular canals of the vestibular system)

– symptoms: dizziness, nausea, vomiting, spinning, and piercing buzzing sounds

• Vertigo (malfunction of the semicircular canals of the vestibular system)

– symptoms: dizziness and nausea

CHEMICAL SENSES

• Taste

– Chemical sense because the stimuli are various chemicals

– Tongue

– Surface of the tongue

– Taste buds

CHEMICAL SENSES (CONT’D)

• Tongue

– Five basic tastes• sweet• salty• sour• bitter• umami: meaty-cheesy taste

CHEMICAL SENSES (CONT’D)

• Taste buds– Shaped like miniature onions– Receptors for taste– Chemicals dissolved in saliva activate taste buds– Produce nerve impulses that reach areas of the

brain’s parietal lobe– Brain transforms impulses into sensations of taste

• Flavor– Combination of taste and smell

Taste

• We have bumps on our tongue called papillae.

• Taste buds are located on the papillae (they are actually all over the mouth).

• Sweet, salty, sour and bitter.

CHEMICAL SENSES (CONT’D)

• Smell, or olfaction

– Steps for olfaction• stimulus• olfactory cells• sensation and memories• functions of olfaction

CHEMICAL SENSES (CONT’D)

CHEMICAL SENSES (CONT’D)

• Smell, or olfaction

– Stimulus• we smell volatile substances• volatile substances are released molecules in the

air at room temperature• examples: skunk spray, perfumes, warm brownies;

not glass or steel

CHEMICAL SENSES (CONT’D)

• Smell, or olfaction

– Olfactory cells• receptors for smell located in a one-inch-square

patch of tissue in the uppermost part of the nasal passages

• olfactory cells are covered in mucus that dissolves volatile molecules and stimulates the cells

• the cells trigger nerve impulses that travel to the brain, which interprets the impulses as different smells

CHEMICAL SENSES (CONT’D)

• Smell, or olfaction

– Sensations and memories• nerve impulses travel to the olfactory bulb• impulses are relayed to the primary olfactory

cortex• cortex transforms nerve impulses into olfactory

sensations• we can identify as many as 10,000 different odors• we stop smelling our deodorants or perfumes

because of decreased responding (adaptation)

CHEMICAL SENSES (CONT’D)

• Smell, or olfaction

– Functions of olfaction• one function: to intensify the taste of food• second function: to warn of potentially dangerous

foods• third function: to elicit strong memories; emotional

feelings

CHEMICAL SENSES (CONT’D)

TOUCH

• Touch

– Includes pressure, temperature, and pain

– Beneath the outer layer of skin are a half-dozen miniature sensors that are receptors for the sense of touch

– Change mechanical pressure or temperature variations into nerve impulses that are sent to the brain for processing

TOUCH (CONT’D)

TOUCH (CONT’D)

• Receptors in the skin

– Skin

– Hair receptors

– Free nerve endings

– Pacinian corpuscle

TOUCH (CONT’D)

• Skin

– Outermost layer– Thin film of dead cells containing no receptors– Just below are first receptors, which look like groups

of thread-like extensions– Middle and fatty layer– Variety of receptors with different shapes and

functions– Some are hair receptors

TOUCH (CONT’D)

• Hair receptors

– Free nerve endings wrapped around the base of each hair follicle

– Hair follicles fire with a burst of activity when first bent– If hair remains bent for a period of time, the receptors

will cease firing– Sensory adaptation– Example: wearing a watch

TOUCH (CONT’D)

• Free nerve endings– Near bottom of the outer layer of skin – Have nothing protecting or surrounding them

• Pacinian corpuscle– In fatty layer of skin– Largest touch sensor– Highly sensitive to touch– Responds to vibration and adapts very quickly

TOUCH (CONT’D)

• Brain areas

– Somatosensory cortex

– Located in the parietal lobe

– Transforms nerve impulses into sensations of touch, temperature, and pain

PAIN

• What causes pain?

– Pain: unpleasant sensory and emotional experience that may result from tissue damage, one’s thoughts or beliefs, or environmental stressors

– Pain results from many different stimuli

PAIN (CONT’D)

PAIN (CONT’D)

• How does the mind stop pain?

– Gate control theory of pain– Nonpainful nerve impulses compete with pain

impulses in trying to reach the brain– Creates a bottleneck or neutral gate– Shifting attention or rubbing an injured area

decreases the passage of painful impulses– Result: pain is dulled

PAIN (CONT’D)

• Endorphins

– Chemicals produced by the brain and secreted in response to injury or severe physical or psychological stress

– Pain-reducing properties of endorphins are similar to those of morphine

– Brain produces endorphins in situations that evoke great fear, anxiety, stress, or bodily injury as well as intense aerobic activity

PAIN (CONT’D)

• Dread– Connected to pain centers in brain– Not the act itself that people fear– Time waiting before event causes dread

• Acupuncture– Trained practitioners insert thin needles into various

points on the body’s surface and then manually twirl or electrically stimulate the needles

– After 10 to 20 minutes of stimulation, patients often report a reduction in various kinds of pain