Sensation and Perception

Sensation

• The process by which our sensory systems (eyes, ears, and other sensory organs) and nervous system receive stimuli from the environment

Sensation• Input comes from the five

senses:

–Visual (Eyes)

–Audio (Ears)

–Cutaneous/Tactile (Touch)

–Olfaction (Smell) (Nose)

–Gustation (Taste) (Tongue)

Receptor Cells

• Each of the five senses is specifically coded to only take in one type of stimulus, whether is be light waves, sound waves, smell, taste, or touch.

Perception

• The process of organizing and interpreting sensory information

• How we recognize, interpret, and organize our sensations

Bottom-Up Processing

• Information processing that focuses on the raw material entering through the eyes, ears, and other organs of sensation

Top-Down Processing

•Information processing that focuses on expectations and experiences in interpreting incoming sensory information

Thresholds

Threshold

• An edge or a boundary

• Walking into the room – on one side you are in the room on the other you are outside of the room

Difference Threshold

• The minimum difference that a person can detect between two stimuli 50% of the time

• Also called just noticeable difference

• (JND)

Absolute Threshold

Detection Threshold

• The minimum intensity of energy required to produce sensation in a receptor cell

• Also known as Absolute Threshold

Absolute Threshold ExampleAbsolute Threshold Example

• Touch: The wing of a bee falling on your cheek from a height of 1 centimeter

Absolute Threshold ExampleAbsolute Threshold Example

• Hearing: The tick of a watch from 6 meters away

Absolute Threshold ExampleAbsolute Threshold Example

• Taste: 1 gram of table salt in 500 Taste: 1 gram of table salt in 500 liters of water – the minimum liters of water – the minimum needed to taste somethingneeded to taste something

Absolute Threshold ExampleAbsolute Threshold Example

• Vision:Vision: A candle flame on A candle flame on a clear night, 30 miles away a clear night, 30 miles away – the minimum needed to – the minimum needed to see it. Doesn’t mean that see it. Doesn’t mean that you can make out what it isyou can make out what it is

Absolute Threshold ExampleAbsolute Threshold Example

• Smell: 1 drop of perfume in a 3 Smell: 1 drop of perfume in a 3 room house.room house.

Signal Detection Theory

• One testable way to determine the thresholds for various people.

• Incremental changes in sound, taste, etc. are made to test for reactions in people. Tone tests (hearing) are an example.

Signal Detection Results

• Hit– signal present and sensed

• Miss– signal present but not sensed

• False Alarm– signal absent, but sensed

• Correct Rejection– signal absent, and not sensed

• IE. Frog eye’s have receptor cells that fire only in response to small, dark, moving objects. Theoretically, a frog would starve to death while knee-deep in motionless flies.

• A male silkworm moth has receptors so sensitive to the odor of a females sex attractant that they can detect even one-billionth of an ounce released, from up to a mile away.

Ernst Weber and Weber’s Law • The greater the magnitude of the

stimulus, the larger the difference must be in order to be noticed– IE. If you are carrying 20 lbs. and add

5 lbs., it’s noticeable. If you are carrying 100 pounds and add 5 pounds, it may not be noticeable. You need to add 10 lbs. to 100 pounds to make it noticeable.

Sensory Adaptation• When exposed to a stimuli over

a period of time there will be a diminished sensitivity to it

• If a stimulus is constant and unchanging, eventually a person may fail to respond to it

Selective hearing

• Do you think it exists?

Selective Attention• Focusing conscious awareness on a

particular stimulus to the exclusion of others

• The ability to focus on one stimulus at a time

• Allows a person to function in a world filled with many stimuli

The Visual System: The Structure of the

Visual System

Cornea• The clear bulge on the front of the

eyeball

• Begins to focus the light by bending it toward a central focal point

• Protects the eye

Parts of the Eye – Cornea

Iris

• A ring of muscle tissue that forms the colored portion of the eye; creates a hole in the center of the iris (pupil)

• Regulates the size of the pupil by changing its size--allowing more or less light to enter the eye

Parts of the Eye - Iris

Pupil

• The adjustable opening in the center of the eye that controls the amount of light entering the eye (surrounded by the iris)

• In bright conditions the iris expands, making the pupil smaller.

• In dark conditions the iris contracts, making the pupil larger.

Parts of the Eye - Pupil

Lens• A transparent structure behind the pupil;

focuses the image on the back of the eye (retina)

• Muscles that change the thickness of the lens change how the light is bent thereby focusing the image

• Glasses or contacts correct problems in the lens’ ability to focus.

Parts of the Eye - Lens

Nearsighted - Myopia

Farsighted - Hyperopia

Retina• Light-sensitive surface with cells that

convert light energy to nerve impulses

• At the back of the eyeball

Parts of the Eye - Retina

Receptor Cells

• These cells are present in every sensory system to change (transduce) some other form of energy into neural impulses.

• In sight they change light into neural impulses the brain can understand.

• Visual system has two types of receptor cells – rods and cones

• Visual receptor cells located in the retina

• Can only detect black and white

• Respond to less light than do cones

Rods

• Visual receptor cells located in the retina

• Can detect sharp images and color

• Need more light than the rods

• Many cones are clustered in the fovea.

Cones

Fovea

• The central focal point of the retina

• The spot where vision is best (most detailed)

Parts of the Eye - Fovea

Visual Processing in the Retina

Visual Processing in the Retina

Visual Processing in the Retina

Visual Processing in the Retina

Optic Nerve

• The nerve that carries visual information from the eye to the occipital lobes of the brain

Parts of the Eye – Optic Nerve

Blind Spot

• The point at which the optic nerve travels through the retina to exit the eye

• There are no rods and cones at this point, so there is a small blind spot in vision.

Parts of the Eye – Blind Spot

The Visual System: Color Vision

Color Vision

• There are two theories of color vision:

–Trichromatic Theory

–Opponent-Process Theory

Can you see what is in the middle?

Trichromatic Theory

• Cones are pre-set to be sensitive to RED, GREEN, and BLUE. All of the colors that we see are combinations of those three colors.

Color Deficient Vision• People who lack one of the three

types of cones• Usually the red or green receptors

are missing

• Usually referred to as color blindness

• In inherited and found more in males

Red-Green Color Blindness

Opponent-Process Theory

• Sensory receptors in the retina come in pairs:–Red/Green–Yellow/Blue–Black/WhiteWhite

• Only one side is “on” at a timeOnly one side is “on” at a time

Opponent Process Theory

ON” “OFF”red greengreen red blue yellow yellow blue black whitewhitewhite white black

Afterimage Effect

Opponent-Process Theory

• If one sensor is stimulated, the other is inhibited

• If one sensor is over-stimulated, and fatigues, the paired sensor will be activated, causing an afterimage

Hearing: The Nature of Sound

Sound

•Sound, like light, comes in waves

•Sound is vibration•Features of sound include:

–Pitch–Hertz–decibels

Pitch

• A sound’s highness or lowness in tone

• Dependent on the frequency of the sound wave – the more “waves per second” the higher the frequency or pitch

• Is measured as hertz (Hz)

Hertz (Hz)

• A measure of the number of sound wave peaks per second; measures “frequency”

• Determines the pitch of the sound

• Human hearing goes from 20 Hz to 20,000 Hz

Decibel (dB)

• A measure of the height of the sound wave

• Determines the loudness of the sound

• Sometimes called amplitude

Hearing: The Structure of the

Auditory System

PINNA

• It collects sound and directs it into the outer ear canal.

Also called the auricle. The

visible part of the outer ear.

Parts of the Ear – Auditory Canal

• The opening through which sound waves travel as they move into the ear for processing

• Ends at the eardrum

Auditory Canal

THE MIDDLE EAR

Eardrum

•Also called the tympanic membrane. A thin membrane that vibrates when sound waves reach it.

• it transfers sound vibration from the air to the tiny bones of the middle ear

•Can be damaged by objects in the ear or exceptionally loud noises

Parts of the Ear – Tympanic Membrane

Ossicles

•Three tiny bones that transfer sound waves from the eardrum to the cochlea

•Hammer, anvil and stirrup–Fun fact: the stirrup is the smallest bone in the human body – only .25 cm

Parts of the Ear - Ossicles

Oval Window

•The point on the surface of the cochlea which receives the sound vibration from the ossicles

•As the oval window vibrates, the fluid in the cochlea vibrates.

Parts of the Ear – Oval Window

• The Ossicles amplify the vibration of the eardrum

Cochlea

•A hearing organ where sound waves are changed into neural impulses (transduction)

•The major organ of hearing•Filled with fluid; a snail

shaped body tube

Parts of the Ear - Cochlea

Hair Cells• The receptor cells for hearing in the

cochlea that change sound vibrations into neural impulses

• Transduction!

Movement of the fluid causes the hair cells to move which causes TRANSDUCTION!

Parts of the Ear - Hair Cells

Auditory Nerve

• The nerve that carries sound information from the ears to the temporal lobes of the brain

Parts of the Ear – Auditory Nerve

Semicircular Canals

•Organs in the inner ear used in sensing body orientation and balance (vestibular sense)

•Relies on fluid in the canals•Spinning in circles disrupts

the fluid.

Parts of the Ear – Semicircular Canals

Divisions of the Ear

• Ear’s structure can be divided into:

–The outer ear

–The middle ear

–The inner ear

Divisions of the Ear

Divisions of the Ear

Divisions of the Ear

Parts of the Ear•Sound waves to Outer Ear-

•Ear Canal, Eardrum (waves bounce on membrane)

•Middle Ear- hammer, anvil, stirrup

•Small bones vibrated by waves

•Oval Window (membrane vibrates)

• Inner Ear- sound waves ripples fluid in cochlea and activates hair cells

How do we hear?Place Theory-Place Theory- different frequencies in sound waves cause vibrations atdifferent placesplaces in the cochlea

High Frequencies

Low Frequencies

Frequency Theory-Frequency Theory- different frequency of the sound wave

vibrates the inner ear at a different rate

EUSTACHIAN TUBE

• A tube that connects the middle ear to the back of the nose; it equalizes the pressure between the middle ear and the air outside. When you "pop" your ears as you change altitude (going up a mountain or in an airplane), you are equalizing the air pressure in your middle ear.

Hearing: Sound Localization

Localization of Sound

• Locating where sound is originating from

• Done through two cues:

–Which ear hears the sound first?

–Which ear hears the louder sound?

Localization of Sound

Problems with hearing• Conduction deafness (middle ear damage)

• Nerve deafness (hair cell or auditory nerve damage)

• Cochlear Implant

Other Senses: Taste

(Gustation)

Taste• Taste is a chemical sense.

• The little bumps on our tongues are actually called papillae

• Inside some of these papillae are clumps of taste cells.

• These clumps of cells are actually the taste buds.

Taste• On average, adults have about 7,500 taste buds.

• These receptor cells are located in the tongue and in the mouth.

• When food dissolves on these receptors, TRANSDUCTION occurs

• Damaged taste receptor cells are replaced within a few days to 2 weeks

• Taste Sensations

–sweet

–sour

–salty

–bitter

- umami (savory-msg)

Supertasters

• People with an abundance of taste receptors

• Approximately 25% of the population

Nontasters

• People with a minimum of taste receptors

• Taste with less intensity than the rest of the population

• Approximately 25% of the population

Other Senses:

Smell• Smell is a chemical sense.• Olfactory receptors/cells in the

upper nasal passages detect molecules in the air.

• Taste and smell interact to produce flavor.

Olfactory Cells

• The chemical receptor cells for smell

• Located in the nasal passages

Smell

Smell

Smell

Other Senses: Touch

Touch• Touch receptors are on the skin• Four basic skin senses are

– Pain– warmth– cold– pressure

• All skin sensations are a combination of these four basic senses

Sensitivity of Diff body to pain

Most Sensitive

• Back of knees

• Neck region

• Bend of elbow

Least Sensitive

• Tip of the Nose

• Sole of foot

• Ball of thumb

Gate-control Theory of Pain

• Pain messages travel on one set of nerve fibers containing pain gates.

• The gates are open when pain is felt.

• Other sensory messages go through another set of fibers.

• The non-pain fibers can close the pain gates to stop the sense of pain.

Other Senses: Body Senses

Kinesthetic Sense•The system for sensing

the position and movement of individual body parts

•Relies on receptor cells from the muscles and joints

•One’s leg “falling asleep” is a disruption of the kinesthetic sense

Vestibular Sense• The system for sensing body

orientation and balance• Relies on fluid in the semicircular

canals of the inner ear• Spinning in circles disrupts the

fluid.

Parts of the Ear – Semicircular Canals

The End