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Sensory Processes. First Hour - How does perception depend on sensory processing?. Transduction of sensory information The visual system as the “prototype” The duplex theory of vision – Rods and cones and visual acuity The visual cycle The stabilized image procedure - PowerPoint PPT Presentation
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First Hour - How does perception depend on sensory processing?
Sensory Processes
Transduction of sensory information
The visual system as the “prototype”• The duplex theory of vision
– Rods and cones and visual acuity• The visual cycle • The stabilized image procedure• Dark adaptation
An exploration of the 6th sense – A test for ESP
Vision Light waves Light-sensitive cells (rods and cones) in retina
Sound waves Pressure-sensitive hair cells in cochlea of inner ear
Audition
Touch
Pain
Taste
Smell
Pressure on skin Sensitive ends of “touch” neurons in skin
Variety of potentially or actually harmful stimuli
Sensitive ends of “pain” neurons in skin and other tissue
Molecules dissolved in fluid on tongue
Chemical-sensitive cells on tongue
Molecules dissolved in fluid on mucous membranes in nose
Sensitive ends of olfactory neurons in mucous membrane
SenseStimulus
Receptors
Scotopic vision: rods•Not very accurate•Highly sensitive•Monochromatic vision
•120,000,000 rods
Photopic vision: cones•Responsible for visual acuity•Not as sensitive as rods•Colour vision•7,000,000 cones
Duplex Theory of Vision:Two types of receptors
Retina (p 185 Gleitman)
Lightentering
To brainvia opticnerveRod Cone
Ganglioncell
Bipolarcell
Photoreceptorlayer
Amacrinecell
Horizontalcell
lightfovea
10º
10º
20º
20º
40º
40º
30º
30º
blindspot
(See Gleitman p. 185)
Geographical Distribution of Retinal Cells
Rods vs. Cones
FoveaBlind spotlight
fovea
blindspot
periphery
periphery
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
-60 -40 -20 0 20 40 60
Distance from fovea (degrees)
Nu
mb
er o
f ce
lls /
sq. m
m. Rods
Cones
(cones)
(rods)
(rods)
What the eye sees:
By daylight, only the central fovea sees clearly and in colour.
On a dark night, only the periphery sees, but only in black and white and with poor resolution. The fovea is “blind.”
The Visual Cycle• Iodopsin• Rhodopsin
The stabilized image procedure
Dark-adaptation curves
10
9
8
7
6
5
4
3
2
1
00 5 10 15 20 25 30
Minutes in the dark
Min
imu
m in
ten
sity
of
ligh
t re
qu
ired
to s
ee
Cone adaptationRod adaptation
“Rod-cone break” at about 7 minutes
Less
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