Sensorimotor Neurophysiology of Active Sensing Overview Dr. Martha Flanders
ACTIVE SENSING
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Transcript of ACTIVE SENSING
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ACTIVE SENSING
Lecture 1: The Senses
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The senses:
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Sensing:
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Sensory encoding:
Sensory organs consist of receptor arrays:
audition
10 m
cochlea
vision
retina10 m
somatosensation
Finger pad~200 m
What receptors tell the brain
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Sensory encoding:
Sensory organs consist of receptor arrays:
audition
10 m
cochlea
vision
retina10 m
somatosensation
Finger pad~200 m
Spatial organization => Spatial coding (“which receptors are activated”)
What receptors tell the brain
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Spatial coding (via passive sensing) would be sufficient had
the world being continuously
flashing on us
and sensory sheets were u n i f o r m
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Passive sensing metaphors
the eye as a camera the skin as a carbon paper
one could think of:
Imprinted on the skin via mechano-receptors
Imprinted on paper via carbon particles
Pressure islight is
Imprinted on the retina via photo-receptors
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However
1. The world is not flashing
and receptors are mostly sensitive to changes
Receptors must move
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Active Sensing:
Sensor organs MOVE in order to obtain information
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However
1. The world is not flashing
2. sensory sheets are not uniform
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finger
Fovea
eye
Fovea => macro movements of the sensory organ
whisker
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Sensor motion is required for
• Foveation• Sensing stationary environment
• Without sensor motion sensation is limited to moving or flashing objects
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How sensor motion constrains sensory coding?
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Eye movements during fixation
backward!
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Eye movements during fixation
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=> Temporal coding (“when are receptors activated”)
Sensory organs consist of receptor arrays:
audition
10 m
cochlea
vision
retina10 m
somatosensation
Finger pad~200 m
Spatial organization => Spatial coding (“which receptors are activated”)
Movements
sensory encoding: What receptors tell the brain
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Some similarities between vision and touch sensation
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whisker
Meissner (RAI)
Merkel (SAI)
Ruffini (SAII)
Lanceolate (RAx)
free endings
Finger pad
SAI SAIIRAI RAII
eye
R G B
Receptor types
SARA PC
Some similarities between vision and touch sensation
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eye
finger
whisker
5’
@ 1o Receptors mix
Some similarities between vision and touch sensation
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Receptor filtering
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1 10 100 1000
SA RA PC
Frequency (Hz)
Touch
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1 10 100 1000
R G B
Frequency (1013 Hz)
Vision
1 10 100 1000
Some similarities between vision and touch sensation
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Receptor convergence / divergence
Human eye: 5M cones + 120M rods --> 1M fibers
Human skin: 2,500 receptors/cm2 --> 300 fibers / cm2
Rat whisker: 2,000 receptors --> 300 fibers
Human ear: 3,000 hair cells --> 30,000 fibers
Some similarities between vision and touch sensation
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eye finger whisker
Receptors
Bipolar cells
Ganglion cells
Thalamus
Cortex
Receptors
Ganglion cells
Brainstem cells
Thalamus
Cortex
Processing stations
Some similarities between vision and touch sensation
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eye finger whisker
Receptors
Bipolar cells
Ganglion cells
Receptors
Ganglion cells
Brainstem cells
Lateral inhibition
Some similarities between vision and touch sensation
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Spatial Encoding
vision
retina10 m
retina – 2D matrix of photorecetors sensitive to light changes
finger tip – 2D array of mechanoreceptors sensitive to skin movement
somatosensation
Finger pad
~10 mm
Some similarities between vision and touch sensation
Whisker pad – 2D array of hairs sensitive to movement
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whiskers – 2D array of whiskers
Spatial Encoding
but ...
Some similarities between vision and touch sensation
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Analogies
Fovea: retinal fovea - finger pad - whisker pad
Some similarities between vision and touch sensation
Sensor motion: an eye - a finger - a whisker