Sensation and Perception

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Sensation and Perception
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• 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.

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

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• 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

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• 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

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Subliminal 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

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A_ _OM_BI_E
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• 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

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• A quick experiment..

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• Webers Law to be perceived as different, two
  stimuli must differ by a constant minimum
  percentage
• In other words, its not the amount of stimuli
  that matters, its the percentage its the ratio
  of the second stimulus to the first
• Light intensity 8
• Weight 2
• Tone frequency - .3

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Other examples

• Suit and sweater, which first?
• New cars

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Sensory 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 wont
  notice it
• So then if you stare at something, shouldnt it
  disappear as the sense receptors in your eye
  become used to it?

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• Yes
• It should..
• It would..
• But
• Your eyes are always moving, even when you stare
• Try this

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Phototransduction

• Conversion of light energy into neural signals
  the brain can understand

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Light 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

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

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Wavelength (Hue)
Violet
Green
Indigo
Blue
Yellow
Orange
Red
400 nm
700 nm
Long wavelengths
Short wavelengths
Different wavelengths of light result in
different colors.
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• Intensity amount of energy in a wave,
  determined by amplitude (i.e. how bright a
  light is)

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Intensity (Brightness)
Blue color with varying levels of intensity. As
intensity increases or decreases, blue
color looks more washed out or darkened.
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The spectrum of electromagnetic energy
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Parts 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)

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• 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

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Rods
Cones
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• Nearsightedness nearby objects are seen more
  clearly
• Farsightedness faraway objects are seen more
  clearly

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• Optic nerve- carries neural impulses from the eye
  to the brain
• Fovea- central point in the retina, where the
  eyes cones cluster
• Blind spot
• See if you can find your blind spot..

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Processing visual information
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Feature Detection
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• Parallel processing processing several aspects
  of a problem simultaneously
• Blindsight seeing without seeing. Huh?

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Color 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

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Color blindness
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• 8 of males show a color weakness, but only .05
  of females
• Whos better at discriminating color?
• Why?

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Opponent-Processing theory

• 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

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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.

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Opponent Colors
Gaze at the middle of the flag for about
30 Seconds. When it disappears, stare at the dot
and report whether or not you see Britain's flag.
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ComplementaryAfterimages
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• 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

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Opponent Process Theory
Hering proposed that we process four primary
colors combined in pairs of red-green,
blue-yellow, and black-white.
Cones
Retinal Ganglion Cells
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Color Constancy

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

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Hearing (audition)
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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
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Parts 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

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• Loudness is determined by the number of activated
  hair cells
• Pitch
• Place theory
• Frequency theory

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How does the brain locate sounds?

• Snap
• Above head
• Directly behind head
• Directly in front of head
• On sides of head

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Hearing loss

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

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• Sensory interaction

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Touch

• 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 cold
• Has learned to move through vision
• What happens when the lights go out?
• Touch localization
• Two-point thresholds

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Pain

• A product of the body and the brain
• Phantom limbs
• Gate control theory
• Sensitivity to pain
• Reducers and Augmenters
• People who feel no pain
• Pain control
• Distraction
• 2.50 pill, and .10 cent pill
• 85 61

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Taste

• Chemical sense
• Taste buds
• Regeneration
• Super tasters- most
• taste buds
• everything is
• intense
• Tasters
• Non-tasters

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Taste
Traditionally, taste sensations consisted of
sweet, salty, sour, and bitter tastes. Recently,
receptors for a fifth taste have been discovered
called Umami.
Sweet
Salty
Sour
Bitter
Umami (Fresh Chicken)
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Taste

• 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
• Smoke heavily
• Consume large amounts of alcohol
• Grow older
• Synesthesia

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Taste

• Culture and taste preferences

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Smell

• 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?

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• Anosmia inability to smell
• Taste
• Weight loss
• Gas appliances
• Body odor
• How good are we at identifying smells?

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• Anticipated Identifiability Actual
  Identifiability
• 1. ammonia 1. Johnsons 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

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• Can you tell someones gender by smelling them?
• Hands experiment 80 accuracy
• T-shirt experiment
• Pheromones
• T-shirts again 6 men
• 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

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Body Position

• Kinesthesis
• Vestibular sense
• One foot balancing
• Chair experiment
• Field dependence/
• independence

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Perception
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What do these letters spell?

• FOLK

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What do these letters spell?

• CROAK

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What do these letters spell?

• SOAK

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

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the wrod as a wlohe.
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Selective 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

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Inattentional Blindness

• 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

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Illusions

• 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

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Poggendorf Illusion
Muller-Lyer Illusion
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Visual Capture

• Vision is the dominant sense when competing with
  other senses

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Gestalt 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

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Organizing principles of Gestalt psychology
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1.) 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?

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2. Grouping

• Proximity
• Similarity
• Continuity
• Connectedness
• Closure

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3. 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

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• 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

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

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• 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

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• Relative motion
• Linear perspective
• Light and Shadow

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4. Motion Perception

• Movies
• Phi phenomenon

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Apparent 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.
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Perceptual Constancy

• Shape and size
• Size and distance
• Lightness

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• Perceptual adaptation
• Perceptual set readiness to detect a particular
  stimulus in a given situation (home alone?)
• FOX OWL SNAKE TURKEY DEER B?ll
• BOB RAY DAVE STEVE TOM B?LL

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• TIME FLIES I CANT THEYRE TOO FAST

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• 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 thats impossible. Is Sally right?

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Which monster is bigger?
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• Look at the Ponzo Illusions below.

Which Line is longer?
Which Elephant is Biggest?
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ESP

• Extrasensory Perception
• Telepathy mind to mind communication
• Clairvoyance ability to sense distant events
• Precognition telling the future
• Psychokinesis ability to move objects with your
  mind

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• 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 dont disappear. This
  should be proof enough, we don't always see what
  we think we see.

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