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Upcoming Read Gregory Article for Feb 23 Read Pinker Article for help with stereo vision and stereo grams Read Land Article for March 2

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 – Retinal image size –far objects smaller than near objects

Retinal image size –problem: big far things same as close small things –“solved” by size constancy: Perceived size is adjusted according to perceived distance (based on other cues) –forms the basis for several visual illusions Pictorial Depth Cues

Retinal image size Pictorial Depth Cues

Retinal image size Pictorial Depth Cues

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

Now on to Magic Eye Stereograms

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

Autostereograms Optically separate images aren’t needed

Autostereograms Optically separate images aren’t needed WARNING! Tricky stuff coming in the next slides

Autostereograms Optically separate images aren’t needed WARNING! Tricky stuff coming in the next slides Keep the definitions of convergence and disparity separate.

Autostereograms Convergence is on a point at the same distance as the images Boxes and faces are on the horopter How many boxes would you see? boxes and faces are on the horopter What would happen if you remove the divider of a stereoscope?

Autostereograms right-eye line of sight crosses left- eye line of sight in front of image (crossed convergence) each retina is now pointed at the opposite box How many boxes would you see? What would happen to the face? crossed convergence Now cross your eyes:

Autostereograms There would be three boxes middle box: right eye sees face shifted to right; left eye sees face shifted to left therefore: uncrossed disparity Face in the middle box appears behind square crossed convergence

Autostereograms What would happen if you moved the faces within the box? What would happen if you viewed this with uncrossed convergence?

Autostereograms Left Eye’s Image Right Eye’s Image Crossed convergence shifts right image to the right of the left image and vice versa:

Autostereograms What would happen if the convergence was uncrossed?

Autostereograms Left Eye Right Eye Uncrossed convergence shifts right-eye’s image to the left of the left-eye image and vice versa:

Autostereograms What would happen if the faces were switched relative to the boxes?

Autostereograms one doesn’t even need two different images!

RIGHT EYELEFT EYE Convergence tells your brain that the plane of the image is farther away than it really is Autostereograms Faces fuse

Autostereograms Uneven spacing between identical objects in a single picture can appear as disparity if the angle of convergence is inappropriate

Autostereograms Uneven spacing between identical objects in a single picture can appear as disparity if the angle of convergence is inappropriate TRICK: Seeing depth in autostereograms requires you to suppress the reflexive coordination between convergence and accommodation

RIGHT EYELEFT EYE If you uncross convergence, your right eye gets these faces shifted slightly to left, left eye gets them shifted to right = CROSSED DISPARITY Autostereograms Any repeating objects that have a spacing different from the background will have either crossed or uncrossed disparity What would you see?

RIGHT EYELEFT EYE If you uncross convergence, right eye gets these faces shifted slightly to right, left eye gets them shifted to left = UNCROSSED DISPARITY Autostereograms Any repeating objects that have a spacing difference from the background will have either crossed or uncrossed disparity What would you see?

Autostereograms by adjusting the disparity at different parts of the image (with a computer usually) one can make shapes that emerge or recede in depth

“Magic Eye” Stereograms Usually viewed with uncrossed convergence Imagine gazing farther than the surface (let your eyes “relax”) Now try to notice objects or forms in the blurriness As you become aware of shapes, try to focus (accommodate) the plane of the image without converging your eyes

Autostereograms