Sensation and Perception - Wofford...
Transcript of Sensation and Perception - Wofford...
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Sensation and Perception
Chapter 5
Vision: p. 135 - 156
Sensation vs. Perception
• Sensation vs. Perception
• Physical stimulus → Physiological response →
Sensory experience & interpretation
• Example vision research questions:
– How does the eye take light and transform it into a
message the brain can understand?
– How do we see a stable world even though our eyes
are constantly blinking and shifting?
– How do perceptual illusions trick the mind?
Visual system Physical properties of light
• Wavelength
– Hue
• Amplitude
– Intensity/brightness
• Mix of wavelengths
– Saturation
The Eye
Transduction
Process to translate
light into an electro-
chemical message for
the brain
Accommodation
Lens changes shape
to focus light on retina
Blindspot demonstration
Demo in text p.141
http://faculty.washington.edu/chudler/chvision.html
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Vision problems Accomodation = shape of lens changes to focus
Flexibility lost with increased age = Presbyopia
http://faculty.washington.edu/chudler/sight.html
The three main layers of the retina
Photoreceptors
Rods – Concentrated in
periphery of retina
– Low light ok
– No detail, no color
Cones – Concentrated in
fovea
– Needs full light
– High visual acuity
– Color receptors
Dark adaptation
Photopigments
have to be
regenerated by
cells
Color theories
Trichromatic theory
H. von Helmholz
Opponent-process theory
E. Herig
Negative afterimage
http://faculty.washington.edu/chudler/after.html
http://michaelbach.de/ot/col_rapidAfterimage/index.html
Text demo p155
Lilac Chaser
• http://michaelbach.de/ot/col_lilacChaser/index.html
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Center-Surround Receptive Fields
• 126 million receptors in
retina
• Convergence allows many
receptors to use 1 neuron
for afferent signaling
• Center-Surround receptive
fields allow for more than 1
signal to be sent by 1
afferent neuron
• Either excitatory or
inhibitory for each region
Luminance and contrast
http://michaelbach.de/ot/lum_herGrid/index.html
Motion perception
• Phi phenomenon
– Max Wertheimer (1912)
– Motion via still images
– http://michaelbach.de/ot/mot_reverse-
phi/index.html
• Motion illusions
– Motion aftereffect
– http://michaelbach.de/ot/mot_adapt/index.html
Rotating Snake
• http://michaelbach.de/ot/mot_rotsnake/ind
ex.html
Thought paper • What perceptual work is required by a
baseball player to hit a baseball?
• Dynamic visual acuity: see moving object, see
rotation of object
• Depth perception: see how far away it is
• Tracking: keep eyes fixed on moving object
• Object recognition: separate object from field
• Contrast sensitivity: see object color against
background color
• Pick up on other cues specific to sport
Object (or Pattern)
Recognition
How do we interpret lines and patterns as objects?
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Gestalt principles of organization
• Laws of “perceptual organization”: see whole
• Figure vs. ground
– Proximity
– Similarity
– Closure
– Good continuation
– Common fate
Which gestalt law?
Gestalt principles
• Group objects together to find the 13
faces
Biological motion
• http://michaelbach.de/ot/mot_biomot/index
.html
• Which gestalt law??
What are the depth cues? Depth perception
• Monocular cues
– Linear perspective
– Acuity
– Color and brightness
– Shadow or occlusion
– Relative height
– Relative motion
http://michaelbach.de/ot/mot_ske/index.html
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Depth perception
• Binocular cues
– Retinal disparity
– Convergence
• Depth illusions
– Ames room
• Perceptual constancies
Pattern recognition
• Bottom-up processing
– Information from sensory receptors
• Top-down processing
– Information from knowledge and expectations
• Specialized receptors in
visual cortex
– Hubel & Weisel , 1962
• Simple cells
– Orientation specific
• Complex cells
– Movement, faces, etc.
• How does brain pull
information together?
Feature detectors
Stimulus
Cell’s
responses
Visual disorders
• Agnosia: deficit in recognizing objects – Book: “The man who mistook his wife for a hat” by Oliver Sacks
– Prosopagnosia ( deficit for faces) • http://www.youtube.com/watch?v=XLGXAiSpN00
• http://www.faceblind.org/
– Akinetopsia (deficit for objects in motion)
• Suggests regions of the cortex designed to
processes certain parts of visual input
• “What” system
– Damage to occipital-temporal pathway
• “Where” system
– Damage to occipital-parietal pathway
Ungerleider & Mishkin (1983)
• Method with monkeys:
– Object discrimination task
– Landmark discrimination problem
• IV: lesion site (temporal lobe vs. parietal lobe)
• Result:
– Object discrimination deficit with temporal lesion
– Landmark discrimination deficit with parietal lesion
Perceptual parsing
• Detect and identify primary 3d objects or geons
(Biederman, 1987)
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Biederman’s Geons
• Intersections are important to recognition
Top-down processing
Top-down processing Tox-Doxn Pxocxssxng
• To xllxstxatx, I cxn rxplxce xvexy txirx
lextex of x sextexce xitx an x, anx yox stxll
xan xanxge xo rxad xt – ix wixh sxme
xifxicxltx
• Why are you able to read the sentence
above?
Another example
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1MPR3551V3 7H1NG5! 1N 7H3
B3G1NN1NG 17 WA5 H4RD BU7 N0W, 0N
7H15 LIN3 Y0UR M1ND 1S R34D1NG 17
4U70M471C4LLY W17H 0U7 3V3N
7H1NK1NG 4B0U7 17, B3 PROUD! 0NLY
C3R741N P30PL3 C4N R3AD 7H15.
PL3453 F0RW4RD 1F U C4N R34D 7H15
Pattern Recognition
• Bottom-up AND top-down
• Bi-directional model
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Perceptual problem solving:
Impossible figures Thought paper
• Think of an example from your life where
you use top-down and bottom-up
processing.
• Explain the example.
• What parts of the example use top-down
processing and what parts use bottom-up
processing?