Successive complexity in the visual system
Photoreceptors are sensitive to light
With reasonable color sensitivity
Retinal ganglion cells are sensitive to simple patterns
Figure: Color-opponent retinal cells detect spot colors in visual field
Successively higher levels of visual processing detect successively more complex features
First in LGN, then in cortex
First patterns and movement, then visual recognition
From Kandel, Schwartz, Jessel, Principles of Neural Science, 3rd edn., 1991, pg. 473