Sensation and Sensation and PerceptionPerception

• Sensation – the process of detecting physical energy and transforming it into neural signals– This transformation process is called

transduction• Perception – selecting, organizing, and

interpreting sensations• Do we see the world as it actually is?

– Nope.• The world we see is a construct of our minds.

There is no color. There is no sound.

• Bottom up processing – Sensation to perception. Body to brain.

• What is the smallest amount of something you can sense?

• Absolute threshold – the minimum amount of stimulation you can detect 50% of the time

• Try it..• Some common absolute thresholds

include:

• Why “50% of the time?”• Signal Detection Theory – our ability to

sense things is influenced by our:– Experience – some people are trained to

detect specific things (police officers)– Expectations – you may/may not be ready

(clowns)– Motivation – you may/may not care– Level of fatigue/alertness – you might be

tired

Subliminal messagesSubliminal messages• Can we be influenced by things below our

absolute threshold?• Can we be manipulated through subliminal

messages?• Yes and no• They may have a brief effect

– Priming• Studies have shown that subliminal

messages do not produce a lasting outcome

A_ _OM_BI_E

• How much does a stimulus have to change before we notice a difference?

• For example, how bright does a light need to be before we can tell it is brighter? How much does a sound need to change before we can tell it is louder?

• Difference Threshold/Just Noticeable Difference (JND)- minimum difference between two stimuli required for detection 50% of the time

• A quick experiment..

• Weber’s Law – to be perceived as different, two stimuli must differ by a constant minimum percentage

• In other words, it’s not the amount of stimuli that matters, it’s the percentage; it’s the ratio of the second stimulus to the first

• Light intensity – 8%• Weight – 2%• Tone frequency - .3%

Other examplesOther examples• Suit and sweater, which first?• New cars

Sensory AdaptationSensory Adaptation• Diminished sensitivity as a result of

constant stimulation• Do you notice the chair pressing against

your legs?• If you put a band aide on, very soon you

won’t notice it• So then if you stare at something,

shouldn’t it disappear as the sense receptors in your eye become used to it?

• Yes• It should..• It would..• But…• Your eyes are always moving, even when

you stare• Try this…

PhototransductionPhototransduction• Conversion of light energy into

neural signals the brain can understand

Light and colorLight and color• Light can behave as a wave or a particle• Wavelength – the distance from the peak of one

wave to the peak of the next

• Hue (color) – dimension determined by the wavelength of light

Wavelength (Hue)

Different wavelengths of light resultin different colors.

400 nm 700 nm

Long wavelengthsShort wavelengths

Violet Indigo Blue Green Yellow Orange Red

• Intensity – amount of energy in a wave, determined by amplitude (i.e. how “bright” a light is)

Intensity (Brightness)

Blue color with varying levels of intensity.As intensity increases or decreases, blue color

looks more “washed out” or “darkened.”

The spectrum of electromagnetic energy

Parts of the EyeParts of the Eye• Cornea – outer covering• Pupil – adjustable opening in center of eye• Iris – muscle that controls the pupil• Lens- transparent structure behind the iris

that changes shape to focus images• Retina – inner surface of the eye. Contains

receptor rods and cones, and a bunch of other neurons (bi-polor, ganglion cells)

Rods peripheral retina detect black, white and gray twilight or low light

Cones near center of retina fine detail and color vision daylight or well-lit conditions

Rods

Cones

• Nearsightedness – nearby objects are seen more clearly

• Farsightedness – faraway objects are seen more clearly

• Optic nerve- carries neural impulses from the eye to the brain

• Fovea- central point in the retina, where the eye’s cones cluster

• Blind spot• See if you can find your blind spot..

Processing visual Processing visual informationinformation

Feature DetectionFeature Detection

• Parallel processing – processing several aspects of a problem simultaneously

• Blindsight – seeing without seeing. Huh?

Color VisionColor Vision• Trichromatic theory (Young-Helmholtz) – since

any color can be created by combinations of red, blue, and green, the eye must have three types of receptors for these three colors

• Subtractive- subtracts wavelengths from the reflected light

• Additive

Color blindnessColor blindness

• 8% of males show a color weakness, but only .05% of females

• Who’s better at discriminating color?

• Why?

Opponent-Processing Opponent-Processing theorytheory

• Yellow is a mixture of red and green light, but people blind to red and green can often see yellow. How is this possible?

• Afterimages

After Images• Stare at the eye of the red parrot while you slowly count to 20, then

immediately look at one spot in the empty birdcage. The faint, ghostly image of a blue-green bird should appear in the cage.

Opponent Colors

Gaze at the middle of the flag for about 30Seconds. When it disappears, stare at the dot and report

whether or not you see Britain's flag.

ComplementaryAfterimages

ComplementaryAfterimages

• In the nervous system, color processing cells are grouped together like this:

• Red-green• Blue-yellow• Black-white• When you stare at one color, you

exhaust that receptor, so when you look at a white page, you see the opponent color

Opponent Process Theory

Hering proposed that we process four primary colors combined in pairs of red-green, blue-

yellow, and black-white.

Cones

RetinalGanglion

Cells

Color ConstancyColor Constancy• Color is relative• The color you see depends on the context

Hearing (audition)Hearing (audition)

What causes sound?What causes sound?• Molecules bump into each other at different rates,

causing small changes in air pressure. Your brain converts these changes to neural impulses that it interprets as sound

• Sound energy is measured in decibels• Absolute threshold for hearing is 0 decibels, a

loud thunder crack is 120

120dB

Parts of the earParts of the ear• Sound travels through your outer ear and causes

your eardrum to vibrate• these vibrations are then transferred to the

middle ear where they cause three bones – called the hammer, the anvil, and the stirrup – to vibrate

• The vibrations cause the fluid in the cochlea to ripple

• These ripples bend tiny hair cells• The hair cells send neural messages to the brain• = hearing

• Loudness is determined by the number of activated hair cells

• Pitch• Place theory• Frequency theory

How does the brain How does the brain locate sounds?locate sounds?

• Snap:oAbove headoDirectly behind headoDirectly in front of headoOn sides of head

Hearing lossHearing loss• Conduction hearing loss• Nerve hearing loss• Cochlear implants• Sensory compensation

• Sensory interaction

TouchTouch• Mixture of pressure, warmth, cold, and pain• Only pressure has specific nerve receptors• Braille – 1824• Ian Waterman – no sense receptors for light

touch, body position and movement, hot and coldo Has learned to move through visiono What happens when the lights go out?

• Touch localization• Two-point thresholds

PainPain• A product of the body and the brain

o Phantom limbs

• Gate control theory• Sensitivity to pain

o Reducers and Augmenters

• People who feel no pain• Pain control

o Distractiono $2.50 pill, and .10 cent pill

• 85%; 61%

TasteTaste• Chemical sense• Taste buds

o Regeneration

• Super tasters- most taste buds

everything is intense

• Tasters• Non-tasters

TasteTasteTraditionally, taste sensations consisted of sweet, salty,

sour, and bitter tastes. Recently, receptors for a fifth taste have been discovered called “Umami”.

Sweet Sour Salty Bitter Umami(Fresh

Chicken)

TasteTaste

• You can become accustomed to tastes (culture?)• Experience plays a role too. Ever gotten sick after

eating a specific food? • Your sensitivity to taste will decline if you:

o Smoke heavilyo Consume large amounts of alcoholo Grow older

• Synesthesia

TasteTaste• Culture and taste preferences:

SmellSmell• Peaks in early adulthood and then declines (like

the other senses)• Chemical sense (receptor cells in nasal cavity)• Not filtered by thalamus• Smell and memories• Who has the best sense of smell?

• Anosmia – inability to smello Tasteo Weight losso Gas applianceso Body odor

• How good are we at identifying smells?

• Anticipated Identifiability Actual Identifiability

• 1. ammonia 1. Johnson’s baby powder• 2. coffee 2. chocolate• 3. mothballs 3. coconut• 4. perfume 4. Crayola crayons• 5. orange 5. mothballs• 6. lemon 6. Ivory soap (bar)• 7. bleach 7. Vicks VapoRub• 8. vinegar 8. Bazooka bubble gum• 9. nail polish remover 9. coffee• 10. peanut butter 10. caramel

• Can you tell someone’s gender by smelling them?o Hands experiment – 80% accuracyo T-shirt experiment

• Pheromoneso T-shirts again – 6 meno Women preferred the men who had an immune

system gene similar to their own (one they inherited from their fathers)

• Subliminal smells – good, bad, and neutral – ratings

Women

Men

10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99Age Group

4

3

2

0

Numberof correct

answers

Women and young adults have best sense of smell

Body PositionBody Position• Kinesthesis• Vestibular sense

o One foot balancingo Chair experimento Field dependence/ independence

PerceptionPerception

What do these letters What do these letters spell?spell?

FOLK

What do these letters What do these letters spell?spell?

CROAK

What do these letters What do these letters spell?spell?

SOAK

• Top-down processing: basically, how we make sense of sensory input

Aoccudrnig to rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in what oredr the ltteers in a wrod are, the olny iprmoetnt tihng is that the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can still raed it wouthit porbelm. This is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

Selective AttentionSelective Attention• We focus on only a small amount of our

experience at a time• But because we can rapidly shift our attention, it

feels like we are able to focus on many things at once

• Cocktail party effect: one voice• Mutli-tasking

Inattentional Inattentional BlindnessBlindness

• We miss things because our attention is directed elsewhere

• Jabbawocky penguin; Gorilla• Change blindness: when our vision is interrupted,

we have a more difficult time noticing changes• Choice blindness: switched photos

IllusionsIllusions

• The firing of certain cells that are sensitive to light-dark boundaries inhibits other cells that would detect the white lines. This blocking process makes you sense darker regions

Muller-Lyer Illusion

Poggendorf Illusion

Visual CaptureVisual Capture• Vision is the dominant sense when competing

with other senses

Gestalt PsychologyGestalt Psychology• From the German word meaning “form” or

“whole”• How does the brain transform a variety of

independent stimuli into a complete representation?

• “Rehfeldt” is also a German word

Organizing principles Organizing principles of Gestalt psychologyof Gestalt psychology

1.) Figure and Ground1.) Figure and Ground• Figure in front of ground• Helps you recognize that objects (like faces) are

separate from their surroundings• Which is figure and which is ground?

2. Grouping2. Grouping• Proximity• Similarity• Continuity• Connectedness• Closure

3. Depth Perception3. Depth Perception• Ability to see objects in three dimensions• Binocular cues – two eyes• Retinal disparity – each eye, and therefore each

retina, receives a slightly different image• 3D movies• Convergence

• Monocular cues• Relative size- object that casts the smaller retinal

image is farther away (if similar in size)• Relative clarity – hazy objects look farther away

• Relative height – objects higher in our field of view are perceived as farther away

• Interposition – if one object blocks our view of another, we see it as closer

• Texture gradient – a change from distinct texture to indistinct texture implies distance

• Relative motion• Linear perspective• Light and Shadow

4. Motion Perception4. Motion Perception• Movies• Phi phenomenon

Apparent MotionApparent Motion

Phi Phenomenon: When lights flash at a certain speed they tend to present illusions of motion. Neon signs use this principle to create motion

perception.

Two lights flashing one after the other.One light jumping from one point to another: Illusion of motion.

Perceptual ConstancyPerceptual Constancy• Shape and size• Size and distance• Lightness

• Perceptual adaptation• Perceptual set – readiness to detect a particular

stimulus in a given situation (home alone?)

FOX; OWL; SNAKE; TURKEY; DEER; B?llBOB; RAY; DAVE; STEVE; TOM; B?LL

• TIME FLIES I CANT THEYRE TOO FAST

• Sally announces to her kindergarten classmates that today is the birthday of both her father and her grandfather. Both are exactly 50. Her teacher says that’s impossible. Is Sally right?

Which monster is bigger?

• Look at the Ponzo Illusions below.

Which Line is longer? Which Elephant is Biggest?

ESPESP• Extrasensory PerceptionoTelepathy: mind to mind

communicationoClairvoyance: ability to sense

distant eventsoPrecognition: telling the futureoPsychokinesis: ability to move

objects with your mind

• If your eyes follow the movement of the rotating pink dot, you will only see one color, pink. If you stare at the black + in the center, the moving dot turns to green. Now, concentrate on the black + in the center of the picture. After a short period of time, all the pink dots will slowly disappear, and you will only see a green dot rotating if you're lucky! It's amazing how our brain works. There really is no green dot, and the pink ones really don‘t disappear. This should be proof enough, we don't always see what we think we see.