Conditions under which stereopsis and motion perception are blind

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Conditions under which stereopsis and motion
perception are blind

• Perception, 2002, volume 31, pages 65 71
• Yong-Guk Kim, John D Mollon

In this article they did experiments on failure
of visual system in stereoscopic depth perception
and perception of coherent motion. We usually see
depth in stereogram (if you know how to look),
but under some conditions this depth perception
is lost. One of these conditions is similar
luminance if luminance is the only difference
between the matching and non-matching
elements. They tried to side step this problem
and they found some interesting results when the
red and green dots are of different size (as in
figure 1). They found out that not when the
elements have the same luminance (a) the depth
perception disappears but when they have a same
luminance flux (b). In the experiments they tried
to confirm these observations.
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Experiment 1 They saw stereograms as in figure 2
and they where asked if the central disk they
should see was in front or behind the rest of the
array. They used 40 randomly ordered trails with
different luminance and with each luminance they
used 3 different sizes. They used 2 subjects for
this experiment, one male (JC) and one female
(SD).
Results The positions of the minima are different
for the diffrent sizes of the green elements.
Those of JC coincided very well with the
calculated flux on which they expected to see the
effect. (vertical arrows)
Figure 3
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Figure 2
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Experiment 2 This was an experiment where the
first author was subject himself. Here they used
random dot kinematograms. The stimulus was about
the same as in experiment 1. This time the
luminance of the red squares was varied as was
the size of green squares. In the experiment a
square in the middle moved eighter vertically
or horizontally. The subject had to choose
between these 2. Results The minimum of the
same-size squares stimuli is where they expected
it to be, but those with smaller green squares
are shifted more to the left.
Figure 3
A random dot kinematogram You see loads of
random pixels, but a group of pixels move around.
You will be able to see that group of pixels
separate from the background.
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General discussion The first experiment shows
that not equal luminance but equal luminance
flux makes a collapse of the depth perception of
a stereogram occur. This is an example of the
fact that one sensory system works differently
from the other. The second experiment reveals
similar limitations in perception.
Fig 4. A stereogram, because I like them ?
Made by Tijmen van Wettum