PSY 162 Lecture Notes - Lecture 16: Visual Cortex, David H. Hubel, Thalamus
Summing & Subtracting
● The photoreceptors send signals to the bipolar cells
○ Who summate their experience
○ Send their message to G cells
■ Inhibitory or excitatory center surround
○ 2 kinds of Ganglion
■ Luminanance cell (Large G/Magno)
● Receives signals from all kinds of cones
Opponent Cells
● Why?
● 2 kinds of answers
○ First is efficiency
■ It is probably useful to analyze color separately from luminance
■ More efficient to code different types of info independently
○ Second is evolutionary
■ We started w/ just blue cones
■ Color vision started after we had a luminance pathway
■ The first step was develop another cones that broadened the range we can
see
■ Retinal G cells add/subtract information rather than try and ?merge?
Systems
What & Where
● The Where stream
○ Uses information from Ganglions that sum cone inputs
● The What system
○ Uses info from G-cells that sum & cells that subtract cone inputs
○ Further divided into a form pathway
■ Color & luminance are combined to define shape
Color Opponency & Mixing Paint
● If you mix
○ Red + green or blue + yellow light = white light
○ Red + green (B-Y) paint = black
○ Interestingly - colors that neutralize one another when you mix them, can enhance
each other when they are adjacent
○ This works because color opponency operates not only at each point in the retina
but also across space to nearby regions of the visual field
○ Also- colors look more vibrant when surrounded by opponent colors
Color Opponency
● What (should have) happened
○ Under bright light - yellow looked brighter & grey bar looked dull
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The photoreceptors send signals to the bipolar cells. Receives signals from all kinds of cones. It is probably useful to analyze color separately from luminance. More efficient to code different types of info independently. Color vision started after we had a luminance pathway. The first step was develop another cones that broadened the range we can see. Uses information from ganglions that sum cone inputs. Uses info from g-cells that sum & cells that subtract cone inputs. Color & luminance are combined to define shape. Red + green or blue + yellow light = white light. Red + green (b-y) paint = black. Interestingly - colors that neutralize one another when you mix them, can enhance each other when they are adjacent. This works because color opponency operates not only at each point in the retina but also across space to nearby regions of the visual field. Also- colors look more vibrant when surrounded by opponent colors.
