SensationSensationandand

PerceptionPerception

What do you feel? What do you feel? You probably feel your rear against your seat.You probably feel your rear against your seat. Ok, now take a whiff around the room – Ok, now take a whiff around the room –

different odors are entering your nose different odors are entering your nose (hopefully something pleasant)(hopefully something pleasant)

Now listen really closely, what do you hear?Now listen really closely, what do you hear? probably the hum from the computer or that probably the hum from the computer or that

guy next to you breathing heavyguy next to you breathing heavy Now try to taste what’s in your mouth. Now try to taste what’s in your mouth. maybe you can dig out a piece of food from maybe you can dig out a piece of food from

your breakfast or maybe you have that your breakfast or maybe you have that morning breath flavor funk going on.morning breath flavor funk going on.

Regardless, at this moment, in some distorted Regardless, at this moment, in some distorted way, you are using all of your senses.way, you are using all of your senses.

Sensation

• The process by which our sensory receptors (sense organs) receive stimulus from the environment.

• What that means is when your body (through our senses) takes in information from everything around us, we are experiencing sensation.

Perception

• The process of organizing and interpreting sensory information

So So sensationsensation is is taking the stuff from outside of us and taking the stuff from outside of us and

bringing it inside our bodies bringing it inside our bodies

and and perceptionperception is is our body trying to understanding and our body trying to understanding and

organizing what we take in.organizing what we take in.

SensationSensation

Important Important ConceptsConcepts

So how does your brain make sense of the So how does your brain make sense of the world and form what you understand as world and form what you understand as

reality?reality? Bottom-Up Processing Bottom-Up Processing (data driven)(data driven)

Our sense of reality starts with our sensations and Our sense of reality starts with our sensations and work up to the brainwork up to the brain

The brain takes the info from the senses and we The brain takes the info from the senses and we develop a sense of realitydevelop a sense of reality

Top-Down Processing Top-Down Processing (experience driven)(experience driven) Our sense of reality begins with our prior experiences Our sense of reality begins with our prior experiences The brain takes our prior experiences and new The brain takes our prior experiences and new

current info and together we develop a sense of current info and together we develop a sense of realityreality

(the brain compares what you are currently seeing with what (the brain compares what you are currently seeing with what you have experienced before)you have experienced before)

Bottom-UpProcessing

Detection viaReceptor cells

(flicker, crackle,Smell

TransmissionTo brain

Change of energyInto information

Organization andInterpretation

Experience, motivation,And expectations (fond

Campfire memories,Expectations of warmth

And friendshipTop-DownProcessing

Behavior, thoughtsAnd emotions(move nearer,warm hands,

Feel comfortable

OutputProcessing(perception)

Input(sensation)

Bottom-Up Processing

• Let’s start off with an important term – transduction

• The process by which our body transforms light, sound, touch, etc. into neural impulses that our brain can understand

TransductionConversion of one form of energy to

another. Stimulus energies changed to neural impulses.

Light Eyes Transduction Neural messages

What you consciously see

Sensory Adaptation• Diminished sensory sensitivity as a

result of constant stimulation.

When you first go into a restaurant you probably notice lots of different food smells. However, the longer you stay the less you notice them. The smells don’t disappear – people just become less sensitive to them.

Do you feel every sensation going on around you??

Can you recall a recent time when, your attention

focused on one thing, you were oblivious to

something else (perhaps to pain, to someone’s

approach, or to background music)?

Selective Attention•The ability to focus on some bits

of sensory information and ignore others

Illusionists hope you have very bad selective attention

Helps us screen out irrelevant stimuli and focus on relevant information

Inattentional Blindness

Inattentional Blindness Failing to see visible objects when we are focusing our attention elsewhere

An example of selective attention is:

The ability to listen to one voice among many.

Cocktail Party Effect

Sensory Interaction

•One sense may influence another

•Smell may influence taste

What if we could sense everything?

Life would hurt.

So we can only take in a window of what is out there.

Psychophysics: the study of the relationship between physical stimuli and our psychological experiences to them. – i.e. is blue really blue??

Measuring the SensesMeasuring the Senses

• Psychologists assess the accuracy of the senses in two ways

Measuring thresholds

Applying the signal detection theorysignal detection theory

ThresholdsThresholds are the idea that our

senses have basic limits.

• There are two types of thresholds– Absolute threshold– Difference threshold (or just noticeable

difference)

Absolute ThresholdAbsolute Threshold The smallest amount of stimulus that a person The smallest amount of stimulus that a person

can reliably detectcan reliably detect If you can just barely hear a sound – then that If you can just barely hear a sound – then that

is your absolute threshold for soundis your absolute threshold for sound

Sight = a candle flame seen at 30 miles on a dark clear night

Hearing = the tick of a watch under quiet conditions at 20 feet

Taste = 1 teaspoon of sugar in 2 gallons of waterSmell = 1 drop of perfume diffused in a small houseTouch = the wing of a bee falling on your cheek from a distance of 1 cm

Some common thresholds

Difference Threshold• The smallest amount of change

needed in a stimulus before we notice the change

• Also known as Just Noticeable Difference (jnd)

Can you tell the difference??Can you tell the difference??

Weber’s Law• Used to measure the difference threshold• The idea that, to perceive a difference between

two stimuli, the change must be proportional to the original intensity of the stimulus– What???– The more intense the stimulus, the more it will need

to change before we notice the difference.

Weight – 10%

Hearing – 5%

Vision – 8%How do businesses use Weber’s Law?? - Movie theater example

Signal Detection Theory• This theory examines how outside

influences effect our sensing of stimuli• The theory says …

– Absolute thresholds are not really absolute– Things like motivation or physical state can

affect what we sense.

Signal Detection Theory Cont.Signal Detection Theory Cont.

• It is the belief that people respond differently to the same signal and the same person may detect a particular signal at one time but not another

• For example – if I am really hungry for meat, I am more likely to smell a hamburger than if I was not

– If I think I smell a hamburger, but it is not really there, that is called a false positive (perceiving stimuli that is not there)

– If a hamburger is grilling right in front of me but I fail to smell it, that is called a false negative (not perceiving a stimulus that is present)Which one is worse??

Subliminal Stimulation• Below one’s absolute

threshold or conscious awareness.

Does this work?

Yes and No

• A few studies did show some small emotional reactivity (called priming a response).

• However, the effects are subtle and fleeting.

SensationsSensations

We will be covering the following We will be covering the following sensessensesVisionVisionHearingHearingTouchTouchTasteTasteSmellSmellBody Position and MovementBody Position and Movement

Of The 5 Senses, Which Would You Choose To Lose? Why?

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SenseSense What Stimulates UsWhat Gets Stimulated

Hearing

Vision

Touch

Pain

Sound Waves

Smell

Taste

Light Waves

Potentially harmful stimuli

Molecules dissolved in fluid

Molecules dissolved in fluid

Pressure on Skin

Pressure-sensitive hair cells in cochlea of inner ear

Light-sensitive rods and cones in retina of eye

Sensitive ends of touch neurons in skin

Sensitive ends of pain neurons in skin and other tissue

Taste cells in taste buds on the tongue

Sensitive ends of olfactory neurons in the mucous membranes

Touch

Touch (Somatosensation)• Touch receptors are on

the skin

• Four basic skin senses are

– Pain, warmth, cold, and pressure

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

•Burning = warmth + cold + pain

Pain• Why do we experience pain??

– Your body’s way of telling you something has gone wrong

• Biopsychosocial Perspective on Pain

Biological Influence• Activity in spinal cord

• Genetic differences in endorphin production

Psychological Influences• Attention to pain

• Learning based on experience• Expectations

Social-Cultural Influences• Presence of others

• Empathy for others’ pain• Cultural expectations

PersonalExperience

Of Pain

Why do we feel Pain? 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 nonpain fibers can close the pain gates to stop the sense of pain.

VisionVision

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VisionVision• Photoreceptors in our eyes gather light • Convert its physical energy into neural

messages • And send it to the occipital lobe in the

brain for decoding and analyzing

That’s basically That’s basically it….it….

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

Retina

• Light-sensitive surface with cells that convert light energy to nerve impulses

• At the back of the eyeball

• Made up of three layers of cells

– Receptor cells

– Bipolar cells

– Ganglion cells

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

Rods

• Visual receptor cells located in the retina

• Can only detect black and white

• Respond to less light than do cones

Cones

• 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.

Rods and Cones

Fovea• The central focal point of the retina

• The spot where vision is best (most detailed)

Types of Vision

Optic Nerve

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

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.

Bipolar Cells• Gather information

from the rods and cones and pass it on to the ganglion cells

• Cells that form the middle layer in the retina

•Pass the information from the bipolar cells through their axons

•Together these cells form the optic nerve.

•The top layer of the cells in the retina

Ganglion Cells

Processing

Why Two Eyes?Why Two Eyes?

• Produces binocular disparity

–Constructing three dimensional world out of two dimensional retinal images

TransductionConversion of one form of energy to

another. Stimulus energies changed to neural impulses.

How is this important when studying sensation?For example:

Light energy to vision.Chemical energy to smell and taste.Sound waves to sound.

Light Eyes Transduction Neural messages

What you consciously see

We only use light energy to We only use light energy to see.see.

HueHue

• The color of light as determined by the wavelength of the light energy

• Includes: red, orange, yellow, green, blue, indigo and violet (ROY G BIV)

• The eye can detect 7 million separate hues

AmplitudeAmplitude

• The brightness of light as determined by height of the wave

• The taller the wave, the brighter the color

What makes up a light wave?

Wavelength

• The distance from the peak of one light wave to the peak of the next.

•The distance determines the hue (color) of the light we perceive.

Intensity

The amount of energy in a light wave.

Determined by the height of the wave.

The higher the wave the more intense the light is. (brightness)

How do we see in color?

What color is this dragon?

Color• The dragon is anything but red.• The dragon rejects the long

wavelengths of light that to us are red- so red is reflected off and we see it.

• Also, light has no real color.• It is just energy turned into color by

our eyes• It is our mind that perceives the color.

Two major color theories!

What enables you to What enables you to perceive color??perceive color??

Young-Helmholtz Trichromatic (three color) Theory

• Realized that any color can be created by combining the light waves of three primary colors

•Guessed that we have 3 different types of photoreceptor cells in our eyes.

•Each with differing sensitivities to different light wavelengths

•Most colorblind people simply lack cone receptor cells for one or more of these primary colors. – Not really blind – just limited in what colors they can see

Click here to simulate color blindnessClick here to simulate color blindness

Opponent-Process Theory• The visual system has receptors that

react in opposite ways to three pairs of colors (red-green, blue-yellow, and white-black). – These are antagonist/ opponent colors.– Light that stimulates one half of the

pair inhibits the other half– Produces afterimages

AfterimagesAfterimages – colors perceived after other, complementary colors are removed

Afterimage Effect

Sensory Disorder

• Synesthesia

• Anosmia

• The boy who sees without eyes