Unit 4
Perception I
Some thought experiments
• What is “color”?
• Is your “red” the same as the “red” of the
person next to you？
• What is a “sound”?
• If a tree falls in a forest and no one is around
to hear it, does it make a sound?
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The Visual System
What did you see?
• Why did you see something different？
• Why do you have to see something similar to
other people?
– The external stimuli are just the materials, visual
perception happens in your visual system. 。
• Your visual system is different from others’, so …it’s
actually not too surprising that you see something
different.
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Where does “seeing”happen?
• The eye?
• http://www.youtube.com/watch?v=ze8VVtBgK7A
Where does “seeing” happen?
• The eye?
• So….the eye is not sufficient.
– But you can’t deny that it is necessary.
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Where does “seeing” happen?
• The eye
retina
lens
Retina
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Retina
• LightAction potentials
– But how do action potentials become perception??
Action potentials
Light
We know a lot about this. 主觀知覺
(Qualia)
We know little about this.
The Visual System
• The retina
– Photoreceptors
• Cones
• Rods
– Bipolar cells
– Ganglion cells
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Demo: Blind Spot
Demo: Blind Spot
• Blind spot
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The Visual System
• Optic nerve
• Optic chiasma
V1
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The Visual System
• Visual pathways
“Where” pathway
Primary visual cortex (V1) “What” pathway
The Visual System
• Nobel Prize 1981‐Hubel & Wiesel
Hubel, D., and Wiesel, T. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. Journal of Physiology (London) 160, 106‐154.
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The visual system
• Receptive field
A is the receptive field of neuron a
The outside
The neurons
a
A
b
B
c
c
The Visual System
• Receptive field of a V1 simple cell
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The Visual System
• https://www.youtube.com/watch?v=8VdFf3eg
wfg
• V1
– Simple cells
– Complex cells
– Hypercomplex cells
Beyond V1
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The Visual System
• Higher cortical areas
– EBA: Extrastriate “body” area
– FBA: Fusiform “body ” area
– FFA: Fusiform “face” area
The Visual System
• Higher cortical areas
– FFA: Fusiform “face” area
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Color Vision
Color Vision
Please be noted: The “light” itself doesn’t contain the color!! • Visible light
– 400‐700 nm (1 nm=10‐9 m)
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Color vision
• How do we see colors??
– Trichromatic theory
– Opponent‐process theory
Color vision
• How do we see colors??
– Trichromatic theory
– Opponent‐process theory
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Trichromatic theory
• We have three kind of “cones”.
Trichromatic theory
• We have three kind of “cones”.
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Color Vision
• We have three kind of “cones”.
Trichromatic theory
• So, for a particular light, the three cones have
three different responses.
– The information of the light is boiled down into
three parameters.
– But, this can’t exaplain the following illusion.
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Demo: Color Afterimage
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Color vision
• How do we see colors??
– Trichromatic theory
– Opponent‐process theory
Color vision
• How do we see colors??
– Trichromatic theory
– Opponent‐process theory
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Opponent‐process theory
• In order to explain the color afterimage, we need
three systems like:
Opponent‐process theory
• And, they indeed have been discovered
– Opponent neurons (retina & LGN)
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Opponent‐process theory
• So…how is the information of the three cones
integrated into the information for the three
opponent neurons?
Color Vision
Cones
opponent cells
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The Retina..
• Light  Action potentials
– But…how do action potentials become perception?
Action potentials
Light
主觀知覺
(Qualia)
700 nm
500 nm
400 nm
我們知道有cone以
及opponent cells
Cone 以及opponent cells的訊息
怎麼變成“紅色”, “綠色“？
Some philosophical issue
• Does color exist? Or it is just an illusion?
– There is no any necessary connection between a
short‐waved light and the feeling of “blue”
– There is no any necessary connection between a
long‐waved light and the feeling of “red”.
– Do you see the same “red” as the person sitting
next to you??
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Some philosophical issue
• Maybe
Your boss sees
You classmate sees
You friend sees
What you see
Hearing
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Hearing
• Imagine a big lake, and you put your
handkerchief on one side of this lake
– Can you use the vibration of this handkerchief to
know what’s happening deep in the lake?
• Do you think it’s hard?
– But this is what your auditory system does.
Hearing
• Physics of Sound
– Frequency
– Amplitude
Frequency＝speed / wave length
W L.
A
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Hearing
• Psychological dimensions of sound
– Pitch
– Loudness
– Timbre
Hearing
• Psychological dimensions of sound
– Pitch
• Frequency: 20~20000 Hz (audible range)
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Hearing
• Psychological dimensions of sound
– Loudness
• Amplitude
Hearing
• Psychological
dimensions of
sound
– Timbre
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Hearing
• The auditory system
Hearing
• https://www.youtube.com/watch?v=PeTriGTE
Noc
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Hearing
• Theories of pitch perception
– Place theory
– Frequency theory
Hearing
• Theories of pitch perception
– Place theory
– Frequency theory
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Hearing
• Theories of pitch
perception
– Place theory
• Different frequencies
produce their most
movement at particular
locations along the
basilar membrane
– High frequency: base of
cochlea
– Low frequency: opposite
end
Hearing
• Theories of pitch perception
– Place theory
– Frequency theory
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Hearing
• Theories of pitch perception
– Frequency theory
• A sounds of 100 Hz will set the basilar membrane
vibrating 100 times per second
– But neurons cannot fire 1000 times per second
– Volley principle
» Several neurons can fire together
Are they really contradictory?
• Theories of pitch perception
– Place theory
• Accounts well for frequency above 1000 Hz
– Frequency theory
• Accounts well for frequency below 5000 Hz
• Between 1000~5000
– Both systems
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Hearing
• Sound localization
– Comparing the
relative times
– Comparing the
relative intensities
Hearing
• What if they are
all the same
– You have to move
your head
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