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Extra Credit for Participating in Experiments
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Extra Credit for Participating in Experiments
Go to www.tatalab.ca to sign up
We are recruiting for a variety of experiments including basic
perception and ADHD
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ADHD Research ProjectWe are specifically recruiting individuals who
have been diagnosed with ADHD and are currently taking medication
Contact Karla at [email protected] for more information or to sign up
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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
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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
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Pictorial Depth Cues
– Retinal image size– far objects smaller than near objects
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• 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
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• Retinal image size
Pictorial Depth Cues
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• Retinal image size
Pictorial Depth Cues
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• Linear perspective
Pictorial Depth Cues
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• Texture gradient
Pictorial Depth Cues
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• Height in the plane
Pictorial Depth Cues
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More Depth Cues
• Pictorial Depth Cues• Physiological Depth Cues• Motion Parallax• Stereoscopic Depth Cues
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Physiological Depth Cues
– Two Physiological Depth Cues1. accommodation2. convergence
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Physiological Depth Cues
– Accommodation
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Physiological Depth Cues
– Convergence
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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?
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Physiological Depth Cues
– Convergence and accommodation are reflexively linked
Under what circumstances might this be a problem?
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Motion Depth Cues
– Motion1. Parallax
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Motion Depth Cues
– Parallax
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Motion Depth Cues
– Parallax– points at different locations in the visual
field move at different speeds depending on their distance from fixation
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Motion Depth Cues
– Parallax
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Seeing in StereoSeeing in Stereo
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Seeing in Stereo
It’s very hard to read words if there are multiple images on your retinaIt’s very hard to read words if there are multiple images on your retina
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Seeing in Stereo
It’s very hard to read words if there are multiple images on your retinaIt’s very hard to read words if there are multiple images on your retina
But how many images are there on yourretinae?
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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?
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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?
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Binocular Disparity
• Binocular disparity is the difference between the two images
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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”
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Binocular Disparity
• Corresponding retinal points
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Binocular Disparity
• Corresponding retinal points
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Binocular Disparity
• Corresponding retinal points
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Binocular Disparity
• Corresponding retinal points
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Binocular Disparity
• Points in space that have corresponding retinal points define a plane called the horopter
The Horopter
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Binocular Disparity
• Points not on the horopter will be disparate on the retina (they project images onto non-corresponding points)
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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
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Binocular Disparity
• points nearer than horopter have crossed disparity
• points farther than horopter have uncrossed disparity
The Horopter
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Binocular Disparity
• Why don’t we see double vision?
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Binocular Disparity
• Why don’t we see double vision?
• Images with a small enough disparity are fused into a single image
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Now on to Magic Eye Stereograms
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Stereograms
Left Eye Right EyeDivider
• 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
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Autostereograms
• Optically separate images aren’t needed
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Autostereograms
• Optically separate images aren’t needed
• WARNING! Tricky stuff coming in the next slides
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Autostereograms
• Optically separate images aren’t needed
• WARNING! Tricky stuff coming in the next slides
• Keep the definitions of convergence and disparity separate.
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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?
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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:
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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
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Autostereograms
• What would happen if you moved the faces within the box?
• What would happen if you viewed this with uncrossed convergence?
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Autostereograms
Left Eye’s ImageRight Eye’s Image
Crossed convergence shifts right image to the right of the left image and vice versa:
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Autostereograms
What would happen if the convergence was uncrossed?
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Autostereograms
Left EyeRight Eye
Uncrossed convergence shifts right-eye’s image to the left of the left-eye image and vice versa:
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Autostereograms
What would happen if the faces were switched relative to the boxes?
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Autostereograms• one doesn’t even need two different
images!
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RIGHT EYE LEFT EYE
Convergence tells your brain that the plane of the image is farther away than it really is
Autostereograms
Faces fuse
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Autostereograms
• Uneven spacing between identical objects in a single picture can appear as disparity if the angle of convergence is inappropriate
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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
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RIGHT EYE LEFT EYE
If you uncross convergence, your right eye gets these faces shifted slightly to left, left eye gets them shifted to right = CROSSED DISPARITY
AutostereogramsAny repeating objects that have a spacing different from the background will have either crossed or uncrossed disparity
What would you see?
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RIGHT EYE LEFT EYE
If you uncross convergence, right eye gets these faces shifted slightly to right, left eye gets them shifted to left = UNCROSSED DISPARITY
AutostereogramsAny repeating objects that have a spacing difference from the background will have either crossed or uncrossed disparity
What would you see?
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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
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“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
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Autostereograms
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Autostereograms
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Autostereograms