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					Sensation and perception
                   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
Physical versus perceptual characteristics

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

                   Differences in wavelength
                   are perceived as differences
                   in color
Wave characteristic of light

                   A and B have same
                   B has higher amplitude

                   Differences in amplitude
                   are perceived as
                   differences in brightness
 Relationship between physical and
 perceptual characteristics of light

Physical feature       How it is perceived

  Wavelength                 Color

  Amplitude                Brightness
Visual transduction

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

                  • Optic disc
                      – How to find
                        your blind spot
                  • Retina
                      – Photoreceptors
                         • Rods
                         • Cones
Rods and cones
                Visual transduction

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

• Optic nerve
• Occipital lobe
• Feature detectors in the brain
  – Respond (fire action potential) only for very specific
     • Some will fire if see horizontal but not vertical line
     • Some will fire if see “L” but not for straight line
Perception of letter “t”
        Summary of visual transduction

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

• Not in the stimulus
  – Species differences
  – No brain; no color
  – Different brain; different color

• Question: What processes give PERCEPTION of
                 The spectrum of light

• White light combination of all colors
  – Longest to shortest wavelenths
     • Red, orange, yellow, green, blue, indigo, violet
     • Infrared and ultraviolet
            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
        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
Examples of color perception
   Trichromatic theory and color blindness

• How does color blindness result according to
• Selective color blindness

• Problems for the trichromatic theory
  – After images
          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
The opponent process theory
            Opponent process theory

• Explanation for after images
         Factors affecting color blindness

• Gender

• Race

• Age

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

• Changes in air pressure
• Tuning fork example
• Compression and expansion of air molecules
          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)
Physical and perceptual properties of
       Relationship between physical and
              perceptual features

Physical property        Perceptual property

Frequency – cycles per   Pitch
second (Hz)

Amplitude – decibels     Loudness
               Different pitches

200 Hz         2000       10,000 (10 kHz)

         16,000 Hz
Species differences in perceiving
                Changes in loudness

Base sound      10 dB louder   20 dB louder

 30 dB louder
                  How to buy stereo speakers
                        Frequency response







Decibel value of some sounds
                   The outer ear


• Pinna
• External auditory canal
                  The middle ear


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


• The cochlea- filled with fluid not air
   – Basilar membrane
   – Hair cells on the basilar membrane
Hair cells
       Transduction in the auditory system

• Changes in air pressure enter the external auditory
• Vibrate the tympanic membrane
• Vibrate the ossicles
• Ossicles “bang” on the cochlea
   – Movement of fluid in cochlea
   – Bending of hair cells
The process of auditory transduction
            Hearing without hair cells
• Cochlear implants
  – Electrodes implanted in cochlear next to auditory nerve
  – Microphone (on belt) receives sound and transmits to
  – Electrodes directly stimulate the auditory nerve
Cochlear implants
                Cochlear implants

• What do they sound like?

Implant               Normal
                       Cochlear implants

• Who should get them
     • Potential disadvantages

• Controversy in deaf community
           Factors that can affect hearing

• Things that can’t 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
Damaged hair cells
Age and hair cell damage
               The “minor” senses

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

• Very young
  – Prefer very sweet foods

• Older adults
  – Lose sensitivity to sweets
  – Many no longer like chocolate

• Receptors in nasal passages respond to specific
• 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

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

• Difference between sensation and perception
  – Receptors transduce information (sensation)
  – Brain interprets that information (perception)

• Prosopagnosia – inability to recognize familiar
  – Can identify facial features (nose, eyes, etc.)
  – Can’t recognize as “Bob”
                 Depth perception

• Should we see in depth?
  – Image on retina

• Binocular disparity
• Demonstration
  – while holding finger near nose alternate blinking
  – Move finger to arm’s length
  – More computation needed when object closer
• Demo – hard to demonstrate but here goes
               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
             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
  – Can simulate this in two dimensions
Retinal image as cue to depth
     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
           Monocular cues to depth (cont’d)

• Texture gradients
   – More densely packed regions appear to be further
            Monocular cues to depth

• Linear perspective – lines in picture converge to a
  vanishing point
Monocular cues to depth

            • Interposition – one object
              blocking another
               Monocular cues to depth

• Motion parallax – when moving more distant objects move slower
          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
               Perceptual constancy
• Critical for maintaining constant perception of
• 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

• Example of size constancy
  – Know that people don’t shrink
  – So perceive constant size – Despite change in size on
    retina (image gets smaller as moves away)
               Example of shape constancy

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

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

                    • Assumption
                      is that room
                      is rectangular
                    • Actual shape
                      is trapezoid
              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
               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
Perceptual grouping -similarity
Perceptual grouping -principle of
    Perceptual grouping - principle of

• Is this organized in rows or columns?
       Perceptual grouping - principle of

• Complete stimuli to form objects
   Importance of figure-ground separation

• What is this a picture of ?
  Importance of figure-ground separation

• Importance of separating background and foreground
Figure-ground confusions
                • Ambiguous figures
                • No clear cues to
                  figure vs. ground
                Pattern recognition

• Bottom up theories
  – Pattern we see determined by features of object
  – Similar to idea of feature detectors

• Biederman’s Geon model
  – Limited set of geons
  – Combine to form all objects
Geons and pattern recognition
                  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
Context – same stimulus different
Effects of context – the moon illusion

                             • Moon illusion
                             • Explanation of
                               moon illusion
               The importance of context

Viewed as is
faces are

Rotated 180
The importance of context

                  A giant bird with a little
                  person in mouth or a
                  man in a canoe being
                  attacked by giant fish
Motion as context
Effects of context

          • Context can make us see
            things that are not really in
            the stimulus
             – Maybe most powerful
               effect of context
                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
Testing depth perception in infants
          The visual cliff
               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
            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
             Visual distortion studies

• Glasses that invert the world
  – Early effects
  – Later effects
  – Perceptual experience

• Video on inverted vision