Binocular Disparity
• points nearer than horopter have crossed disparity
• points farther than horopter have uncrossed disparity
The Horopter
Binocular Disparity
• Why don’t we see double vision?
Binocular Disparity
• Why don’t we see double vision?
• Images with a small enough disparity are fused into a single image
Binocular Disparity
• Why don’t we see double vision?
• Images with a small enough disparity are fused into a single image
• The region of space that contains images with close enough disparity to be fused is called Panum’s Area
Binocular Disparity
• Panum’s Area extends just in front of and just behind the horopter
Binocular Disparity
• Panum’s Area extends just in front of and just behind the horopter
• Images outside of Panum’s area are often blurry because accommodation is reflexively set according to vergence
Stereopsis
• Our brains interpret crossed and uncrossed disparity as depth
• That process is called stereoscopic depth perception or simply stereopsis
Stereopsis
• Stereopsis requires that the brain can encode the two retinal images independently
Stereopsis• Primary Visual cortex
normally keeps input from the eyes separate
• If normal input is restricted during development, the cortical representation of the “bad” eye is reduced
• Amblyopia can result
Amblyopia
• Amblyopia is a visual deficit in which one eye has poor vision because the brain never developed the ability to use signals from that retina
Amblyopia
• Amblyopia is a visual deficit in which one eye has poor vision because the brain never developed the ability to use signals from that retina
• Usually caused by – strabismus - when eyes don’t lock onto the same
point – anisometropia - when one eye has very bad
optics and the other is normal
Amblyopia
• People with Amblyopia can’t see stereograms
Stereograms
• seeing depth requires “only” two different images on the retina
Stereograms• seeing depth requires “only” two
different images on the retina
• this could be accomplished by an optical device that projects separate images into the two eyes
Presenting Binocular Images
• Various ways to add depth:– 1. Stereoscope
Stereograms
Left Eye Right EyeDivider
•Right eye sees face to the right; left eye sees face to the left therefore:uncrossed disparity
•Face appears behind the square
Stereograms
Left Eye Right EyeDivider
What would you see?
Stereograms
Left Eye Right EyeDivider
•Right eye sees face to the left; left eye sees face to the right therefore:crossed disparity
•Face appears in front of square
Presenting Binocular Images
• Various ways to add depth:– glasses with different lenses
Presenting Binocular Images
• Various ways to add depth:– glasses with different lenses
Presenting Binocular Images
• Various ways to add depth:– glasses with different lenses
Presenting Binocular Images
• Various ways to add depth:– LCD Shutter Glasses
Gregory
Science
• Science is like a set of procedures:
Identify a question
Make a Hypothesis
Make a Prediction
Test ItPrediction holds
Prediction Fails
Example: The horizontal-vertical illusion
Example: The horizontal-vertical illusion
• Question:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently
• Prediction:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently
• Prediction: Stabilized image should eliminate the illusion
• Test:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently
• Prediction: Stabilized image should eliminate the illusion
• Test: Illusion is still present in afterimage!
