1. 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
Dark adaptation
An exploration of the 6th sense – A test for ESP

2. Sense Stimulus Receptors Vision Audition Touch Pain Taste Smell
Light waves
Light-sensitive cells (rods
and cones) in retina
Vision
Audition
Touch
Pain
Taste
Smell
Sound waves
Pressure-sensitive hair cells in cochlea of inner ear
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

3. Duplex Theory of Vision:
Two types of 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

4. Retina (p 185 Gleitman) Photoreceptor Bipolar layer cell Ganglion cell
Light
entering
Amacrine
cell
Horizontal
To brain
via optic
nerve
Rod
Cone

6. (See Gleitman p. 185)
40º
30º
20º
10º
fovea
light
blind
spot

7. Geographical Distribution of Retinal Cells Rods vs. Cones
180000
Rods
160000
Cones
140000
120000
100000
Number of cells / sq. mm.
80000
60000
40000
20000
-60
-40
-20
Blind spot 20 40 60
periphery
(rods)
Distance from fovea (degrees)
fovea
Fovea
(cones)
light
blind
spot
periphery
(rods)

8. 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.”

9. The Visual Cycle
Iodopsin
Rhodopsin
The stabilized image procedure

10. Dark-adaptation curves
Cone adaptation
Rod adaptation 10 9 8 7 6 5 4 3 2 1
More
“Rod-cone break” at about 7 minutes
Minimum intensity of light
required to see
Less
Minutes in the dark