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!