psyc 413

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mrsbotelloj
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199760
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psyc 413
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2013-02-11 14:59:19
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perception
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ch 1-4
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  1. Perception –
    • study of how we notice,
    • recognize & add meaning to the world around us
  2. What is this? 
    Perceptual Process
  3. Environmental Stimuli
    • All the things in the environment we can
    • possibly perceive
  4. Attended Stimulus
    • The object that
    • becomes the center of our attention
  5. Stimulus on
    Receptor
    • Look directly at the
    • object of interest – image is formed on receptors of the retina –
    • transformation of object into an image
  6. Transduction
    • Transformation of one form of energy to
    • another

    • E.g., ATM – when you press the “withdrawal”
    • button on the screen, pressure exerted by your finger is converted into
    • electrical energy – sends signals to mechanisms that push your money out
  7. Neural Processing
    • Light energy entering
    • retina – sends signals to activate neurons, which activate other neurons –
    • “message is passed on”
  8. Perception
    • Electrical signals
    • are transformed by the brain into an “experience” (or awareness) or the object
  9. Recognition
    • Our ability to place the object in a category
    • & give it meaning, e.g., “table”

    Problem – Agnosia – inability to recognize objects
  10. Agnosia
    • inability to recognize
    • objects
  11. Action
    • Moving the head or
    • eyes
  12. Knowledge
    • Any information that
    • the perceiver brings to the situation – e.g., I already know the difference
    • between a table & a chair
  13. Bottom-up (data)
    processing
    • –Understand based on
    • incoming data
  14. Top-down
    (knowledge-based) processing
    • –Understand based on
    • prior knowledge

    • –What you already know
    • influences what you learn from the environment
  15. Measuring Perception 5 levels
    • (1) Description 
    • (2) Recognition
    • (3) Detection 
    • (4) Magnitude
    • estimation
    • (5) Search
  16. Measuring Perception
    (1) Description 
    • –Ask the observer to
    • describe what they see – “all the people sitting in the student section are
    • wearing red”
  17. Measuring Perception
    (2) Recognition
    • –Ask the observer to
    • place the stimulus in a particular category – “Number 22 is the other team’s
    • quarterback”
  18. Measuring Perception
    (3) Detection 
    • Absolute threshold
    • Difference
    • threshold (DL)
  19. Measuring Perception
    (4) Magnitude
    estimation
    • –How large/strong/bright
    • is a stimulus?

    • –The nature of light - at higher
    • intensities – doubling the intensity leads to only a small change in perceived
    • brightness – response compression – e.g., bright
    • flashlight

    • –The nature of electricity – doubling the
    • strength of a shock more than doubles the perceived sensation of being shocked
    • – response expansion

    • –The nature of line lengths – perceived length
    • is proportionate to changes in actual length

    –Steven’s Power law
  20. Measuring Perception
    (5) Search
    • –In previous cases,
    • observer has time to make leisurely responses



    • –What about situations
    • when there is time pressure? – e.g., air traffic controller, luggage screener,
    • quality control inspector



    • –Measure of perception
    • – reaction time

       
  21. Measuring Perception
    (3) Detection 
    Absolute threshold
    3 levels
    • –(1) Method of Limits
    • –(2) Method of Adjustment
    • –(3) Method of Constant Stimuli
  22. Measuring Perception
    (3) Detection Absolute threshold
    3 levels
    1. Method of Limits:
    • Present stimuli is
    • ascending or descending order & observer says at what point the light
    • becomes barely visible
  23. Measuring Perception
    (3) Detection Absolute threshold
    3 levels
    2. Method of Adjustment:
    • Observer adjusts
    • stimulus energy in a continuous manner until the stimulus is barely detectable
  24. Measuring Perception
    (3) Detection Absolute threshold
    3 levels
    3. Method of Constant
    Stimuli
    • Experimenter presents
    • 5-9 different stimuli in random order – observer says “yes” when they detect
    • the stimulus

    • Threshold – the
    • stimulus is detected 50% of the time
  25. Measuring Perception
    (3) Detection Absolute threshold
    3 levels
    which is the most accurate but slowest?
    –Method of constant stimuli  
  26. Measuring Perception
    (3) Detection Absolute threshold
    3 levels
    which is the least accurate but fastest?
    Method of Adjustment
  27. Difference
    threshold (DL)
    – 
    • minimum
    • detectable difference between two stimuli
  28. Measuring Perception
    (4) Magnitude estimation
    The nature of light:
    • at
    • higher intensities – doubling the intensity leads to only a small change in
    • perceived brightness – response
    • compression – e.g.,
    • bright flashlight
  29. Measuring Perception
    (4) Magnitude estimation
    The nature of electricity:
    • doubling
    • the strength of a shock more than doubles the perceived sensation of being
    • shocked – response expansion
  30. Measuring Perception
    (4) Magnitude estimation
    The nature of line lengths:
    • perceived
    • length is proportionate to changes in actual length


  31. Structure of the Brain
    • Research on how the
    • brain connects to perception – cerebral cortex, 2mm-thick layer covering brain
    • surface
  32. Neurons
    • Carry electrical
    • signals from brain to the rest of the body

    • Key components of
    • neurons
  33. Neurons
  34. Neurons
    Electrical signals
    • transmitted
    • through a solution rich in ions (molecules that carry electrical charge)  that surround neurons
  35. Neurons:
    solution outside axon is rich in: 
    solution inside the axon is rich in:
    • outside:+ve charged sodium ions;
    • inside: –ve charged potassiumions
  36. resting potential
    • Negative
    • charge inside the neuron is called 
  37. “action potential” or “nerve impulse”
    • If
    • neuron’s receptor is activated, +ve
    • sodium ions rush into the neuron & -ve
    • potassium ions rush out – 
  38. Permeability
    • property
    • of cell membrane – ease with which molecules can pass through membrane
  39. Refractory period
    • limit
    • to the number of nerve impulses that can be carried down a neuron – 500-800
    • impulses per second
  40. Spontaneous activity
    •  firing in the absence of stimuli from
    • environment
  41. Synapse
    • small
    • space between neurons – how do nerve impulses flow across this space?
  42. Neuron
    releases a chemical called 
    neurotransmitters
  43. “neurotransmitters” – flow into the
    synapse into small areas called 
    receptor sites
  44. Excitatory
    transmitters
    cause the inside of neuron to become more positive – depolarization
  45. Inhibitory
    transmitters
    • cause
    • the inside of neuron to become more negative - hyperpolarization
  46. Electromagnetic
    spectrum
    • light
    • rays (electromagnetic energy) of varying wavelengths 
  47. Visible light
    • electromagnetic
    • spectrum that humans can perceive
  48. Photons
    small packets of energy
  49. Wavelength + photons
    important properties for perception
  50. Cornea & lens
    (light rays first pass);
    pupil (dilates in darkness or constricts in brightness);
    retina (final surface on which image is projected)
    – 
    • lens “accommodates” or
    • adjusts its shape to bring the image to focus on the retina 
  51. Ciliary muscles
    • responsible for
    • accommodation – closer objects-rounder shape, farther objects-flatter shape;
    • natural resting point of the lens “resting state”; send message to receptors in
    • the brain
  52. myopia
    (nearsightedness); 
  53. presbyopia
    (farsightedness)
  54. Near point
    • distance at which your lens can no longer
    • adjust to bring an object into focus – near point increases as a person gets
    • older (presbyopia)
  55. Rods
    night vision
  56. cones
    day/bright vision
  57. Rods (night vision) and cones (day/bright
    vision) – receptor cells in the brain. Properties:
    • 1) Location: middle of retina (fovea) – only cones;
    • periphery – more rods & few cones; cones decrease rapidly moving farther
    • from fovea



    • 2) One
    • area in the retina – no receptors – place where optic nerve leaves the eye – “blind spot”



    • 3) “Blind spot” –
    • off to the side of our visual field, where objects are not in sharp focus



    • 4) Most
    • of the time, we don’t notice the blind spot – the brain “fills in” the gap from experience
    • 4) Color sensitivity: rods are color blind – color perception
    • decline in dim light & at night



    • 5) Adaptation: when
    • stimulated by direct light rods lose their sensitivity & take a long
    • time to regain – temporary blindness – e.g., entering a darkened movie theater.
    • Cones
    • become hypersensitive in low light – glare from lights at night.



    • 6) Differential
    • wavelength sensitivity: rods are insensitive to long
    • (red) wavelengths – red objects look black at night, illuminating objects in
    • red light will not affect vision at night
  58. “blind spot”
    • One area in the retina –
    • no receptors – place where optic nerve leaves the eye
  59. Color sensitivity
    • rods are color blind –
    • color perception decline in dim light & at night
  60. Adaptation
    • when stimulated by direct
    • light rods lose
    • their sensitivity & take a long time to regain – temporary blindness –
    • e.g., entering a darkened movie theater. Cones become hypersensitive in low light – glare
    • from lights at night.
  61. Differential wavelength sensitivity:
    • rods are
    • insensitive to long (red) wavelengths – red objects look black at night,
    • illuminating objects in red light will not affect vision at night
  62. Macular degeneration
    • older people, a part of
    • the cone-rich fovea & area surrounding it is destroyed – creates a “blind
    • spot” in central vision
  63. Retinitis pigmentosa
    • genetic – peripheral
    • receptors are destroyed 
    • 1. Macular degeneration
    • 2. Retinitis pigmentosa
  64. Visual pigment molecules
    • large protein called opsin; small light-sensitive
    • molecule called retinal
  65. opsin
    large protein called 
  66. retinal
    • small light-sensitive
    • molecule 
  67. Measuring cone adaptation 
    • look directly at the test
    • light so the light falls on the cone-rich fovea
  68. Measuring rod adaptation
    • can only be measured in
    • people with no cones – a genetic defect called rod monochromats
  69. Cones are more sensitive in the
    beginning – after ______mins, cones finish adapting & sensitivity
    levels off
    3-5
  70. Rods catch up after about ___ mins
    & continue to adapt for the next ____mins
    • 7
    • 20-30
  71. rod-cone break
    • Place where rods begin to
    • determine dark adaptation 
  72. pigment bleaching
    • When visual pigments
    • absorb light, retinal separates from opsin & retina becomes lighter in color
  73. visual pigment regeneration
    • occurs in the dark –
    • determines speed at which sensitivity is adjusted
  74. Cone pigment – ____ mins to
    regenerate completely
    6
  75. Rod pigment – 30
    mins to regenerate
    • Rod pigment – 30
    • mins to regenerate
  76. Rods are more sensitive to
    ___ wavelengths – most sensitive to light of 500 nm
    short
  77. Cones are sensitive to ____
    wavelengths – most sensitive to 560nm
    longer
  78. Purkinje shift 
    • more sensitive to blue-green (short wavelengths) & less sensitive to red
    • (long wavelengths) – effective night lights are generally
    • shades of blue/green – this shift is called 
  79. Purkinje Shift Demo
    • Bright light (photopic)
    • Dusk (mesopic)
    • Night (scotopic)
  80. Convergence
    • when many neurons send
    • signals to one neuron in the retina
  81. convergence is greater in rods 
    • since all signals converge
    • into one, there are fewer neural response units – poorer visual acuity
  82. When searching for
    something (familiar face), the image needs to be focused
    on the 
    fovea for us to recognize it
  83. cones have
    better 
    • visual acuity (ability to
    • see detail)
  84. Foveal cones are more
    ____ packed than peripheral rods
    • Foveal cones are more
    • densely packed than peripheral rods
  85. Rods take over from
    ____ in the dark 
    • Rods take over from
    • cones in the dark – which is why vision is poorer in the dark
  86. Lateral Inhibition
    • Activity in one
    • neuron decreases activity in another
    • – e.g., illumination of neighboring receptors inhibits firing of one receptor
  87. (1)Hermann grid: seeing spots at intersections
    • Mach Bands: seeing borders more
    • sharply
  88. “dark band” 
    • area appears darker than
    • it is
  89. light band
    • area appears lighter than
    • it is
    • Simultaneous
    • Contrast:
    • perception of brightness of one area or color is affected by the presence of an
    • adjacent or surrounding area
  90. Receptive field
    • of
    • a neuron in the visual system is the area on the retina that influences the
    • firing rate of the neuron
    • Area A – not part of the neuron’s receptive
    • field, stimulating this area causes no change in neural activity

    • Area B – excitatory
    • area –
    • stimulating causes increase in neuron’s firing rate

    • Area C – inhibitory
    • area –
    • stimulating causes decrease in neuron’s firing rate

    • Center-surround receptive field – center region
    • responds one way, surrounded by a region that responds another way

    Excitatory-center-inhibitory-surround receptive field
  91. Selective adaptation
    • when
    • we view a stimulus with a specific property, neurons tuned to that property
    • fire
  92. Method: Selective Adaptation
  93. Contrast sensitivity 
    • how
    • sensitive people are to the differences between light & dark bars
  94. Orientation
    • angle
    • relative to horizontal
  95. Contrast
    • difference in
    • intensity of light & dark bars

    • –After being adapted to a certain level of intensity,
    • contrast sensitivity to dark & light decreases
  96. Adapting to wide-grating bar decreased responding of neurons that respond best to wide bars – right bars appear more ____
     narrow
  97. Adapting to
    narrow-grating bars decreased responding of
    neurons that respond best to narrow bars – right
    bars appear more ___
    wide
  98. Neural plasticity 
    • response properties
    • of neurons can be shaped by a person’s perceptual experience
  99. Selective rearing
    • if
    • an animal is reared in an environment that contains only certain types of
    • stimuli, neural plasticity will cause neurons to respond best to that type of
    • stimulus
  100. Maps
    • surface
    • of retina is mapped onto the visual cortex – adjacent
    • points on the cortex correspond to adjacent areas on the retina
  101. Columns
    • neurons
    • with similar properties are organized as columns in the visual cortex – how an object is represented or what it “looks like
  102. Streams
    • sequence
    • of interconnected structures that serve specific functions – what to do, how to do
  103. Modules
    • certain
    • areas that are specialized to serve specific functions – recognizing faces, objects
  104. Each point on the
    object is imaged onto points in the 
    ____
    retina
  105. Each point on the
    retina corresponds to a point on the 
    lateral geniculate nucleus (LGN)
  106. Correspondence
    between points on the LGN & points on the retina 
    • retinotopic map on LGN & in visual
    • cortex
  107. cortical
    magnification factor
    • Small fovea
    • presenting a large image on the cortex – cortical magnification factor
  108. Positron
    emission tomography (PET)
    • person
    • is injected with a small dose of radioactive tracer that is not harmful –
    • enters bloodstream, accompanied by changes in blood flow, provides a measure of
    • blood flow to track which areas of brain are being activated
  109. Subtraction
    technique
    • brain
    • activity is first measured in a “control” state before stimulation (object) is
    • presented – then measured again when the person manipulates the object
  110. Functional
    magnetic resonance imaging (FMRI)
    • similar
    • to PET, but takes advantage of ferrous (iron/hemoglobin) molecules in the blood
    • by presenting a magnetic field – causes ferrous (hemoglobin) molecules to line
    • up like tiny magnets
  111. How is an object
    represented in the cortex? 
    • –We know that – each
    • point on the object forms a corresponding retinotopic image on the LGN & visual cortex
  112. –What does the image
    of the object “look” like?
    • –The image is distorted
    • compared
    • to the actual object – magnification factor allots more space on the cortex
    • specifically to parts of the image that fall on the fovea
  113. COLUMNS
  114. –Large stimulus 
    – stretchesacross the retina – stimulates a number of different orientation columns
  115. –Cortical
    representation of the stimulus does not have to 
    resemble the stimulus
  116. –The length of the
    peppermint stick is represented in different cortical columns in the visual
    cortex – each column
     contains neurons that fire
  117. Object
    discrimination (“what is it?”)
    • e.g., monkey – pick the object that contains food (object discrimination
  118. Landmark
    discrimination (“where is it?”)
    • e.g., monkey – pick the object that is closest in distance to the cylinder –
    • (landmark discrimination)
  119. the “what” pathway or “ventral pathway” 
    Temporal lobe 
  120. the “where pathway” or “dorsal pathway”
    Parietal lobe 
  121. disrupted
    object discrimination task
    • Temporal
    • lobe removal
  122. disrupted landmark discrimination task
    –Parietal lobe –
  123. The ventral &
    dorsal pathways are ____

    Signals flow in __
    directions
    • The ventral &
    • dorsal pathways are connected

    • Signals flow in both
    • directions
  124. Argument
    • dorsal
    • &
    • ventral streams should also be called “how (instead of “where”) & “what”
    • pathways
    • Rod-frame illusion –
    • matching task vs. grasping task
  125. module
    • A
    • structure that is specialized to process information about a particular type of
    • stimulus 
  126. Structures located
    along the dorsal & ventral pathways are specialized to process information
    about specific
    visual quantities
    - modularity
  127. “Face neurons
    • monkey’s
    • cortex – some neurons fired in response to pictures of faces & did not fire
    • in response to non-face stimuli (landscape, food)
  128. Damage to temporal lobe – affects ability
    to 
    recognize faces – prosopagnosia (difficultyrecognizing familiar faces, though they can recognize them easily when theyhear them talk)
  129. prosopagnosia
     (difficulty recognizing familiar faces, though they can recognize them easily when they hear them talk)
  130. fusiform face area (FFA)
    • also responds to
    • pictures in which the presence of a face is implied – e.g., body with a blurred
    • image where the face
  131. Parahippocampal
    place area (PPA)
    – activated by indoor & outdoor scenes
  132. Extrastriate body area (EBA)
     – activated by body parts but not faces

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