Binocular Disparity points (C) nearer than fixation (P) have crossed disparity points (F) farther than fixation have uncrossed disparity

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

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 (V1) has bands of neurons that keep input from the two eyes seperate

Stereopsis If the brain only gets normal signals from one eye early in life, that eye’s neurons crowd out the other eye’s neurons

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

Pinker: How the mind works 3-D Stereograms in Pinker: How the mind works

Infinity of Interpretations There are an infinite number of interpretations of the 2D pattern of light on the retina

Infinity of Interpretations There are an infinite number of interpretations of the 2D pattern of light on the retina The brain selects one that matches with common experience

Infinity of Interpretations There are an infinite number of interpretations of the 2D pattern of light on the retina The brain selects one that matches with common experience Ames Room is example of how this can lead to an illusion

Infinity of Interpretations Ames Room

Adding stereoscopic depth cues to 2D pictures

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

Stereograms Divider Left Eye Right Eye Right eye sees same image as left eye Face appears in same plane as square

Stereograms Divider Left Eye Right Eye What would you see?

Stereograms Divider Left Eye Right Eye Right eye sees image to the right; left eye sees image 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 image to the left; left eye sees image to the right therefore: crossed disparity Face appears in front of square

Presenting Binocular Images Various ways to add depth: 1. Stereoscope

Presenting Binocular Images Various ways to add depth: 2. glasses with different lenses

Presenting Binocular Images Various ways to add depth: 2. glasses with different lenses

Presenting Binocular Images Various ways to add depth: 2. glasses with different lenses

Presenting Binocular Images Various ways to add depth: 3. LCD Shutter Glasses

Autostereograms Optically separate images aren’t needed

Autostereograms Right eye sees image to the right; left eye sees image to the left therefore: uncrossed disparity Face appears behind square crossed convergence

Autostereograms What the image is doing: Left Eye Right Eye What the eyes are doing:

Autostereograms Right eye sees image to the left; left eye sees image to the right therefore: crossed disparity Face appears in front of square uncrossed convergence

Autostereograms What the images are doing: Right Eye Left Eye What the eyes are doing:

Autostereograms one doesn’t even need two different images!

RIGHT EYE LEFT EYE Convergence tells your brain that the plane of the image is behind the plane of the surface