Download Accommodation and Convergence

Stereoscopic Depth
• Disparity between the two retinal images
indicates an objects distance from the plane
of fixation
Stereoscopic Depth
• Disparity between the two retinal images
indicates an objects distance from the plane
of fixation
• Two different images (containing disparity)
can be presented independently to each eye
or…
Stereoscopic Depth
• Disparity between the two retinal images
indicates an objects distance from the plane
of fixation
• Two different images (containing disparity)
can be presented independently to each eye
or…
• Uneven spacing between identical objects in
a single picture can appear as disparity if
the angle of convergence is inappropriate
Autostereograms
• Seeing depth in autostereograms requires
you to suppress the reflexive coordination
between convergence and accommodation
Autostereograms
Any repeating objects that have a spacing difference from the
background will have either crossed or uncrossed disparity
RIGHT EYE
LEFT EYE
If you uncross convergence, your right eye gets image shifted
slightly to left, left eye gets image shifted to right =
CROSSED DISPARITY
What would you see?
Autostereograms
Any repeating objects that have a spacing difference from the
background will have either crossed or uncrossed disparity
RIGHT EYE
LEFT EYE
If you uncross convergence, right eye gets image shifted
slightly to right, left eye gets image shifted to left =
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
Auto (aka Magic Eye)
Stereograms
• Usually viewed with uncrossed convergence
(leads to crossed disparity)
• 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
Autostereograms
Autostereograms
The Correspondence Problem
• What is the Correspondence Problem?
The Correspondence Problem
• What is the Correspondence Problem?
– How does the brain know what contours to
match up…what images correspond?
The Correspondence Problem
• Maybe shape analysis is done first to make
it easier to match up corresponding parts
The Correspondence Problem
• Bela Julesz
tested this with
random-dot
stereograms
• No contours or
form available in
monocular
image!
• Surface in depth
still visible
Left Eye
Right Eye
The Correspondence Problem
• A different model must be adopted:
The Correspondence Problem
• A different model must be adopted:
Visual system can extract form
by matching up individual
elements (dots) in an image,
computing disparity between
them, and finding the most
likely surfaces.
Might this involve top-down
mechanisms? How could you test
that hypothesis?
Next Time: Color Vision
• Read Land Article for Friday