Motion Stereopsis (Binocular Depth-from-Motion, BDFM)


Uploaded by ahwang0216 on 06.06.2009

Transcript:
Motion stereopsis, also known as binocular depth-from-motion, is an important dynamic
binocular vision, yet frequently overlooked and has not been tested in ordinary ophthalmic
clinic.
We designed on personal computer screen 4 moving squares. 3 of them move from side to
side; the other one jumps in depth. The task ofthe observer is to point out which one among
these 4 squares is moving in depth.
Please put on the red/blue goggles, blue one over right eye, and enjoy this fantastic dynamic
depth sensation. Got it? Now try to occlude one eye, either eye will be ok. The depth
sensation no more exists. This tells us that this depth sensation comes from binocular
interaction; it¡¦s an important category of binocularity. Got it?
The answer appears on the next screen. It¡¦s the right one jumping in depth.
How about this one?
The lower one jumping in depth.
Both eyes fixate on a target. When the target is moving toward you, moving in depth, its
image on right and left eyes actually move in opposite direction.
When the target moves sideway, its image over both retina move in the same direction
As the target move toward different direction in the space, it makes different motion vector
combination over two eyes. Conversely, from the combination of two motion vectors on two
retinas, there is enough computational information to recover the motion of the target in space.
This is what it really looks like as the motion stereopsis test is going on.
We explained the task to kindergarten children, and it¡¦s not difficult for them to understand.
Going into some details about the design. For that one square jumping in depth, the
retinal images of two eyes move back and forth in opposite direction.
There are two pairs of stereograms, in time 1 and time 2 respectively. Comparing two half-stereograms
for left and right eye, the backgrounds have identical random-dot pattern, and the squares
in blue color have identical random-dot pattern. In time 1 the squares are crossed displaced
and looks coming in front of the background; in time 2 the squares are uncrossed displaced
and looks going recessed behind the background. There is slender rectangular area in each
half-stereogram that doesn¡¦t appear in another half-stereogram. It¡¦s called monocular
area and its width equals the DISPARITY of the stereogram. Comparing the left images
at time 1 and time 2. The blue squares have identical random-dot pattern and it constitutes
a random-dot kinematogram. The square moves back and forth along repeated time 1 and time
2. This is the source of the image MOTION.
For those 3 squares going sideway, the retinal images of two eyes move in the same direction.
There is no disparity between left and right eyes, and it¡¦s not stereogram pairs. But
the random-dot kinematogram still holds. Images of both eyes move in the same direction and
the fused image goes in sideway.
Besides test the static random-dot stereopsis, which comes from the DISPARITY cue,
We test on personal computer the MOTION stereopsis.
In conventional stereopsis, the depth sensation comes from DISPARITY between two half stereograms.
It¡¦s static stereopsis.
We live in a dynamic world. What we see and the retinal images as well, are always in
motion. Clinically it¡¦s important for us to test the depth sensation coming from relative
MOTION of two retinal images. We call it motion stereopsis, dynamic stereopsis, or considering
its mechanism, call it ¡¥binocular depth-from-motion¡¦.
In strabismic clinic, many patients have near ortho eye position, either after operation
or without surgery. But these signs usually made them fail the stereopsis test. Nevertheless
many of them could pass motion stereopsis test. In the past 5 years, we have collected
about 200 such patients in our clinic. What¡¦s most impressing to us are the infantile esotropia
and latent nystagmus. These two imply early onset strabismus and static random-dot stereopsis
is almost impossible for them. But they do have binocular interaction, they passed binocular
depth-from-motion test.
Going into further details. The above mentioned test is two stereograms presented alternately.
It contained both disparity and motion cues. We tried to separate these two things. If
the squares of two half-stereograms have different random-dot pattern, it¡¦s no more stereogram,
it becomes random-dot correlogram. The backgrounds of two images are correlated while the squares
are uncorrelated.
The left one contains both disparity and motion cues. The middle one, it¡¦s two correlograms
jumping back and forth. No disparity, not stereograms. But the random-dot kinematogram
holds, and it contains MOTION cue only. The right one jumping between two stereograms.
DISPARITY cue holds yet motion cue disappears.
This shows how did we manipulate the random-dot patterns to make them identical or different,
OR partial different by changing the random-dot density of the operator.
A test containing both disparity and motion cues
Got it? Monocularly you see square moving leftward and rightward. This is MOTION cue,
retinal image motion.
Answer is upper one.
A test containing motion cue only.?
A bit more difficult. Got it?
Answer is left one.
A test containing disparity cue only.
Got it? See there is no motion cue. The square is not shifting, it¡¦s flickering.
Answer is right one.
Those patients with near ortho eye position yet failed static stereopsis test could, at
1st step, pass the motion test containing both disparity and motion cues. The 2nd step,
they could pass the test with motion cue only and the 3rd step, they failed the test with
disparity cue only.
We therefore know their depth sensation comes from MOTION cue rather than DISPARITY cue.
We told the patients or the parents, despite they can not read static 3D pictures on the
books, they are able to enjoy 3D movies.
Hope you have enjoyed the journey with Motion Stereopsis, also known as Binocular Depth-from-Motion.
Setting it up at the clinic, you¡¦ll get more information about BINOCULARITY besides
static stereopsis.