Reading Gregory 24 th Pinker 26 th

Seeing Depth What’s the big problem with seeing depth ?

Seeing Depth The world is 3D, the retina is 2D !

Depth Cues  Pictorial Depth Cues: aspects of 2D images that imply depth  Physiological Depth Cues: Proprioception in ocular muscles indicates accommodation and convergence  Motion Depth Cues: foreground and background move in opposite directions  Stereoscopic Depth Cues: disparity between two retinal images indicates distance

Pictorial Depth Cues – Occlusion

Pictorial Depth Cues – Shadows and Shading

Pictorial Depth Cues – Retinal image size –far objects smaller than near objects

Linear perspective Pictorial Depth Cues

Texture gradient Pictorial Depth Cues

Height in the plane Pictorial Depth Cues

More Depth Cues Pictorial Depth Cues Physiological Depth Cues Motion Parallax Stereoscopic Depth Cues

Physiological Depth Cues – Two Physiological Depth Cues 1. accommodation 2. convergence

Physiological Depth Cues – Accommodation

Physiological Depth Cues – Convergence

Physiological Depth Cues – Convergence – small angle of convergence = far away – large angle of convergence = near – What two sensory systems is the brain integrating? – What happens to images closer or farther away from fixation point?

Physiological Depth Cues – Convergence and accommodation are reflexively linked Under what circumstances might this be a problem?

Motion Depth Cues – Motion 1. Parallax

Motion Depth Cues – Parallax

Motion Depth Cues – Parallax – points at different locations in the visual field move at different speeds depending on their distance from fixation

Motion Depth Cues – Parallax

Seeing in Stereo

It’s very hard to read words if there are multiple images on your retina

Seeing in Stereo It’s very hard to read words if there are multiple images on your retina But how many images are there on your retinae?

Binocular Disparity Your eyes have a different image on each retina –hold pen at arms length and fixate the spot –how many pens do you see? –which pen matches which eye?

Binocular Disparity Your eyes have a different image on each retina –now fixate the pen –how many spots do you see? –which spot matches which eye?

Binocular Disparity Binocular disparity is the difference between the two images

Binocular Disparity Binocular disparity is the difference between the two images Disparity depends on where the object is relative to the fixation point: –objects closer than fixation project images that “cross” –objects farther than fixation project images that do not “cross”

Binocular Disparity Corresponding retinal points

Binocular Disparity Corresponding retinal points

Binocular Disparity Corresponding retinal points

Binocular Disparity Corresponding retinal points

Binocular Disparity Points in space that have corresponding retinal points define a plane called the horopter The Horopter

Binocular Disparity Points not on the horopter will be disparate on the retina (they project images onto non-corresponding points)

Binocular Disparity Points not on the horopter will be disparate on the retina (they project images onto non-corresponding points) The nature of the disparity depends on where they are relative to the horopter

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