PSY 162 Lecture Notes - Lecture 5: Mythbusters
Rods
● At night -we are colorblind
○ We only have 1 type of Rod-
■ So it can only send one type of signal
■ How much light is present
■ The brain has no way to know if changes in signal are because of changes
in wavelength
Rods & Reds
● We have about 2x as many red cones as green
● Only 1% are blue-
● So cone response is rather weak in the blue range
● Red appears brighter than blue under the same illumination
Rods
● Are also more sensitive generally to light
○ But are more sensitive to short wavelengths than cones
○ WHen light is high -Red appears brighter- but
○ In low light-we are more sensitive to blues
Changing Light, Changing Sight…
● It is overly simplistic to say that rods do not perceive color
○ They are relatively more sensitive than cones to the short-wavelengths
● Thus in low light-
○ Reds look rather colorless…
○ Blues and greens “pop”
More red cones in bright light, so you can see red better in bright light. The cells are responsive
to red in bright light. When the light is dim this sensitivity decreases.
Dark Adaption of Rods & COnes
● Mythbusters
○ http://www.youtube.com/watch?v=ZhMnPREi1w
○ 1:30
Dark Adaptation Curve
● Adjusting to the dark occurs in 2 stages
○ Rapid adjustment by the cones
○ Then the rods- much more slowly
● Over the course of 20-30 minutes
○ Sensitivity increases 100,000 times
○ 20-30 minutes is about the same time it takes for the sun to rise/set
find more resources at oneclass.com
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Document Summary
We only have 1 type of rod- So it can only send one type of signal. The brain has no way to know if changes in signal are because of changes. We have about 2x as many red cones as green. So cone response is rather weak in the blue range. Red appears brighter than blue under the same illumination. Are also more sensitive generally to light. But are more sensitive to short wavelengths than cones. When light is high -red appears brighter- but. In low light-we are more sensitive to blues. It is overly simplistic to say that rods do not perceive color. They are relatively more sensitive than cones to the short-wavelengths. More red cones in bright light, so you can see red better in bright light. The cells are responsive to red in bright light. When the light is dim this sensitivity decreases. Adjusting to the dark occurs in 2 stages.
