Sensation and perception

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Sensation and perception
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Sensory psychology

• How we know about the world
• General principles
• Transduction
• receptors
• Adequate stimulus
• Law of specific nerve energies
• Battery experiment
• Physical properties give rise to perceptual
  features
• Color is NOT a property of light

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Physical versus perceptual characteristics

• Need to determine relationship between physical
  and perceptual characteristics
• Vision light travels in waves
• Definition of wavelength

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Wave characteristic of light
Differences in wavelength are perceived as
differences in color
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Wave characteristic of light
A and B have same wavelength
B has higher amplitude
Differences in amplitude are perceived as
differences in brightness
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Relationship between physical and perceptual
characteristics of light
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Visual transduction

• Cornea
• Light enters eye
• Pupil
• Contraction and dilation
• Iris
• Pigmented part
• Lens
• Focuses light on retina

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Visual transduction

• Optic disc
• How to find your blind spot
• Retina
• Photoreceptors
• Rods
• Cones

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Rods and cones
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Visual transduction

• Photochemicals in rods and cones respond to
  light
• Fire action potential
• Are carrots really good for your eyes?

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Properties of rods and cones

• Cones (about 7 million in each retina)
• Respond best to bright light
• Respond to color
• Difficult to see color in dark
• Rods (about 120 million in each retina)
• Respond best to dim illumination
• Do not respond to color

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From retina to perception

• Optic nerve
• Occipital lobe
• Feature detectors in the brain
• Respond (fire action potential) only for very
  specific stimuli
• Some will fire if see horizontal but not vertical
  line
• Some will fire if see L but not for straight
  line

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Perception of letter t
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Summary of visual transduction

• Adequate stimulus for vision is light
• Enters the eye and is focused on retina
• Retina has receptors (neurons) with
  photochemicals
• Fire action potential when exposed to light
• AP to occipital lobe via optic nerve

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Color perception

• Not in the stimulus
• Species differences
• No brain no color
• Different brain different color
• Question What processes give PERCEPTION of
  color?

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The spectrum of light

• White light combination of all colors
• ROYGBIV
• Longest to shortest wavelenths
• Red, orange, yellow, green, blue, indigo, violet
• Infrared and ultraviolet

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Theories of color vision

• Do not know exactly how perceive color
• Trichromatic theory (Young-Helmholtz)
• Found three different kinds of cones
• Each has different photochemical
• 3 different photochemicals respond best to 3
  primary colors (red, green blue)
• Any color can be made from combination of primary
  colors

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Trichromatic theory of color vision

• Show a color (pink)
• All three cones types respond (fire)
• Cone type most responsive to red fires most
• Cone types most responsive to green and blue fire
  less
• INTERPRETATION of pattern is pink

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Examples of color perception
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Trichromatic theory and color blindness

• How does color blindness result according to
  theory?
• Selective color blindness
• Problems for the trichromatic theory
• After images

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The opponent process theory

• Photochemicals in cones arranged in opposed pairs
• Red-Green
• Blue-Yellow
• Black White
• Colors oppose one another
• When see red prevents from seeing green

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The opponent process theory
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Opponent process theory

• Explanation for after images

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Factors affecting color blindness

• Gender
• Race
• Age

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Hearing

• General questions same as for vision (and all
  other senses)
• What is adequate stimulus ?
• How does adequate stimulus get transduced (cause
  action potential)
• Physical properties map on to perceptual
  characteristics

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Adequate stimulus

• Changes in air pressure
• Tuning fork example
• Compression and expansion of air molecules

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Physical properties of sound

• Changes in air pressure can be fast or slow
• Many or few cycles (compression-expansion) per
  second (Hertz Hz)
• Frequency
• Air pressure changes can be high or low
• Amplitude
• Measured in decibels (after AGB)

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Physical and perceptual properties of sound
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Relationship between physical and perceptual
features
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Different pitches
10,000 (10 kHz)
2000 Hz
200 Hz
16,000 Hz

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Species differences in perceiving frequencies
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Changes in loudness
Base sound
10 dB louder
20 dB louder
30 dB louder
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How to buy stereo speakers
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Decibel value of some sounds
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Pinna
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The outer ear
Pinna

• Pinna
• External auditory canal

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The middle ear
Pinna

• Tympanic membrane (ear drum)
• Ossicles hammer, anvil and stirrup

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The inner ear
Pinna

• The cochlea- filled with fluid not air
• Basilar membrane
• Hair cells on the basilar membrane

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Hair cells
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Transduction in the auditory system

• Changes in air pressure enter the external
  auditory canal
• Vibrate the tympanic membrane
• Vibrate the ossicles
• Ossicles bang on the cochlea
• Movement of fluid in cochlea
• Bending of hair cells

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The process of auditory transduction
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Hearing without hair cells

• Cochlear implants
• Electrodes implanted in cochlear next to auditory
  nerve
• Microphone (on belt) receives sound and transmits
  to electrodes
• Electrodes directly stimulate the auditory nerve

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Cochlear implants
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Cochlear implants

• What do they sound like?

Normal
Implant
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Cochlear implants

• Who should get them
• Potential disadvantages
• Controversy in deaf community

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Factors that can affect hearing

• Things that cant control
• Age
• Gender
• Things that can control
• Noise
• Duration and amplitude both important
• Frequency
• What frequencies important for speech
• What frequencies noise damages
• Environmental noise vs. loud music
• walkman phenomenon

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Damaged hair cells
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Age and hair cell damage
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The minor senses

• Smell, taste, and touch
• Are they really minor
• Which sense would you LEAST like to lose

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Smell and taste

• Both chemical senses
• Adequate stimulus is specific chemical compound
• Smell
• Transducers are receptors in nasal passage
• Respond only to specific shape of chemical
  compounds
• Taste
• Transducers are taste buds on tongue
• Respond to 4 primary sensations

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Tastes are interpreted

• Overall taste determined by combinations of
  firing of taste buds
• Taste after effects
• Similar to visual after effects
• Due to fatiguing of specific taste buds
• Drink distilled water after very sweet water
• Orange juice immediately after brushing teeth

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Age and taste

• Very young
• Prefer very sweet foods
• Older adults
• Lose sensitivity to sweets
• Many no longer like chocolate

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Smell

• Receptors in nasal passages respond to specific
  chemicals
• Humans relatively poor at identifying smells
• Large gender differences
• Males better at identifying
• Musk active ingredient in most perfumes
• Brut after aftershave
• Females better at
• Juicy fruit gum, coconut, and prune juice

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Pheromones

• What are they?
• Importance in other species
• Importance in humans?
• Coordination of menstrual cycles in women living
  together?
• Males 100,00 times more sensitive to musk than
  women

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Perception

• Difference between sensation and perception
• Receptors transduce information (sensation)
• Brain interprets that information (perception)
• Prosopagnosia inability to recognize familiar
  faces
• Can identify facial features (nose, eyes, etc.)
• Cant recognize as Bob

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Depth perception

• Should we see in depth?
• Image on retina
• Binocular disparity
• Demonstration
• while holding finger near nose alternate
  blinking
• Move finger to arms length
• More computation needed when object closer
• Demo hard to demonstrate but here goes

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Explanation of demo

• Created by combining two different views using a
  special camera
• When focus behind (relax or defocus) you can
  reinstate the slightly different views
• Brain will then combine

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Monocular cues to depth

• Can perceive depth even with one eye
• Based on experience in real world
• Size of retinal image
• In real world smaller images on retina mean
  object is further
• Can simulate this in two dimensions

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Retinal image as cue to depth
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Is the man in the blue shirt the same size in
both images?
Is the image of man in tie the same size?
With depth cues
Without depth cues
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Monocular cues to depth (contd)

• Texture gradients
• More densely packed regions appear to be further

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Monocular cues to depth

• Linear perspective lines in picture converge to
  a vanishing point

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Monocular cues to depth

• Interposition one object blocking another

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Monocular cues to depth

• Motion parallax when moving more distant
  objects move slower

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Summary of depth perception

• Depth is perceived (created by brain)
• Not in stimulus
• Stimulus is 2-D image on retina
• Cues we use based on experience in real world
• Both monocular and binocular cues

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Perceptual constancy

• Critical for maintaining constant perception of
  world
• Knowledge of world contributes to perception
• Two people stand next to one another
• One starts to move away
• We do not perceive the moving person as getting
  smaller
• Example of size constancy
• Know that people dont shrink
• So perceive constant size Despite change in
  size on retina (image gets smaller as moves away)

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Example of shape constancy

• Image on retina changes as angle of opening
  changes
• Still perceive door as same

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Illusions

• Use assumptions we make to fool us
• Ames room example

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Explanation of Ames room

• Assumption is that room is rectangular
• Actual shape is trapezoid

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Perceptual organization

• Idea of perception
• what you see is NOT necessarily what you get
• Perception based on
• Sensation
• Knowledge and experience
• Understanding how we organize our world
• Visual experience not just series of action
  potential in rods and cones

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Gestalt Psychologists

• School lasted from 1920-1950
• Developed principles about how organize
  perception
• Many still hold today
• Some Gestalt principles
• Principles of perceptual grouping
• Figure ground relationships

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Perceptual grouping -similarity
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Perceptual grouping -principle of continuation
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Perceptual grouping - principle of proximity

• Is this organized in rows or columns?

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Perceptual grouping - principle of closure

• Complete stimuli to form objects

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Importance of figure-ground separation

• What is this a picture of ?

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Importance of figure-ground separation

• Importance of separating background and foreground

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Figure-ground confusions

• Ambiguous figures
• No clear cues to figure vs. ground

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Pattern recognition

• Bottom up theories
• Pattern we see determined by features of object
• Similar to idea of feature detectors
• Biedermans Geon model
• Limited set of geons
• Combine to form all objects

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Geons and pattern recognition
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Importance of context

• Context surrounding elements, angle of viewing,
  motion
• Things other than the stimulus itself
• Bottom-up theories predict same stimulus, same
  pattern
• But not necessarily true
• Importance of context

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Context same stimulus different perception
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Effects of context the moon illusion

• Moon illusion
• Explanation of moon illusion

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The importance of context
Viewed as is faces are similar
Rotated 180
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The importance of context
A giant bird with a little person in mouth or a
man in a canoe being attacked by giant fish
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Motion as context
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Effects of context

• Context can make us see things that are not
  really in the stimulus
• Maybe most powerful effect of context

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Perception in infants

• Nature vs. nurture
• Importance of learning for perception
• Is there learning with sensation?
• Not all of one or the other
• Some likely nature
• Binocular disparity
• Some likely nurture
• Interposition, linear perspective

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Testing depth perception in infantsThe visual
cliff
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Learning and perception

• Visual cliff certain perceptual abilities
  learned
• Cochlear implants
• Sensations are not speech
• Can learn to interpret as speech
• Restored sight
• Blind learn to identify object by touch
• Operation to eliminate blindness
• Will they be able to identify object by sight
• Limitations on these studies

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Visual deprivation studies

• Normal kittens have neurons in occipital lobe
  respond to diagonal lines
• Effects of contact lenses that only allow kittens
  to see vertical and horizontal (not diagonal
  lines)
• Remove prior to age of 3 months
• Remove after age of 3 months

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Visual distortion studies

• Glasses that invert the world
• Early effects
• Later effects
• Perceptual experience
• Video on inverted vision