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 Divider Left Eye Right Eye Right eye sees face to the right; left eye sees face to the left therefore: uncrossed disparity Face appears behind the square

Stereograms Divider Left Eye Right Eye What would you see?

Stereograms Divider Left Eye Right Eye 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 Make a Hypothesis Identify a question Make a Prediction Science is like a set of procedures: Make a Hypothesis Identify a question Make a Prediction Prediction Fails Prediction holds Test It

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!