370: Color Perception Pt3, Perceiving Depth and Size

1. Dichromatic
1. Three Types
1. Protanopia: missing L cones
1. They are missing the long-wavelength pigment
1. L cones are responsible for red
2. Typically called red-green color blindness because they can't distinguish between those two colors
2. Affect 1% of males and .02% of females
3. Neutral point occurs at 492nm and above the neutral point they see yellow
2. Deuteranopia: missing M cones
1. They are missing the medium-wavelength pigment
1. M is responsible for green
2. Affects 1% of males and .01% of femals
3. See s-wavelengths as blue
4. Nurtral point occurs at 498 nm and above this point they see yellow
3. Tritanopia: missing S cones
1. S is responsible for blue
2. Affects ..002% of males and .001% of femals
3. see s waves as blue
4. Neutral point at 570 nm
2. Perceiving color Under Changing Illumination
1. Color constancy
1. Perception of colors as relatively constant in spite of changing light sources
2. Sunlight has approximately equal amounts of energy at al visible wavelengths
3. Tungsten has more energy in the long wavelengths so it looks more orangish
4. Chromatic Adaptation
1. If you are looking at a green paper with light shining on the paper and another light shining on you then...
1. white light on the green paper and your eye then paper appears green
2. If red light is on the paper and white light on your eye then your perception is more reddish
3. If red light is on both your eye and the paper the it will appear more green again but still slightly shifted towards red

Perceiving Depth and Size

1. Binocular Cues
1. The two eyes get slightly different views of the world and create depth perception - (diplopia and stereopsis)
2. Thumb test
2. Angular Disparity
1. All points in visual space fall on points on the retina which can be mapped according to distance from the fovea.  
2. Angular Disparity = angle in the right eye - angle in the left eye
3. For all points in the same depth of space will have an angular disparity of 0
1. These visual points are known as the horopter
1. This horopter creates an imaginary circle that goes around your eyes (I really don't quite understand what this is so you might wanna look it up)
2. the right eye and the left eye would both be receiving visual stimuli at the same degree
2. Things that are closer than the horopter will yield a greater than 0 degrees disparity (+)
1. Crossed eyes/angular disparity
3. Things that are further than the horopter will yield a less than 0 degrees disparity (-)
1. Uncrossed angular disparity/eyes
4. Stereopsis
1. For points in visual space close to the depth of fixation, images from the eyes are fuse, resulting in stereopsis
2. Provides very fine depth information
3. Stereo depth in info is based on the degree diff in the two eyes
4. Random Dot Stereogram
3. Top-Down: Random Patterns
1. Some people will report pictures in random-dot patterns when none are there
4. Correspondence Problem
1. How does the visual system match the parts of images from the two eyes?
1. Matches by features
1. Really not a sufficient answer yet.  It's still unknown
5. Physiology
1. Depth perception begins as early as VI, with disparity=selective simple and complex cells
1. But most depth processing takes place in later areas, such as V3