[visionlist] Trying to demonstrate stereoscopic vision remotely

Lester Loschky loschky at ksu.edu
Fri Mar 20 22:45:14 -04 2020

Hi Everybody,

If you teach Sensation and Perception, and are currently preparing to teach
it remotely, you may have the same question I have: how can you demonstrate
stereovision remotely?

As preface, the following are methods I have used in in-person classes to
demonstrate stereo vision:

   1. an actual stereoscope and example stereoimages to share with students
   (including the classic Julesz square tile random-dot-stereogram image)
   2. example stereoscopic lenticular lens images to share with students
   3. red/green anaglyph images with sets of cardboard & plastic red/green
   anaglyph glasses
   4. Google Cardboard plus cell phone to share with students
   5. random dot autosterographic images
   6. touching two pen tips together using two eyes versus one eye
   7. learning about crossed vs. uncrossed disparity using two fingers at
   different distances

Unfortunately, my students don't uniformly have access to the apparatuses
required for 1-4 above.

Re. # 3 (red/green anaglyph images), I've thought of having students order
a single pair of red/green anaglyph glasses online.  However, it appears
that the cardboard and plastic ones can only be purchased in bulk. (I guess
they're too cheap to sell individually.)  They also might not arrive in
time, but students could still enjoy them once they get them.

Re. #4 (Google Cardboard), I recall getting a free Google Cardboard from
the NYTimes several years ago.  However, they are now no cheaper than $5
(Irisu, of India), and likely wouldn't arrive in time.

Regarding option #5 (random-dot autostereograms), I have found that since
seeing random dot autostereographic images in depth requires perceptual
learning, a large proportion of students don't manage to learn (within the
short time period given in a single class period).  (Of course, many
students may have a lot of time on their hands now, so they might keep at
it long enough to learn to perceive them.  But there will definitely be a
good proportion of students who don't try long enough to learn, and so
don't get it.)

#6 (touching two pen tips together) is definitely something that can be
done remotely.  However, it doesn't have the "Wow!" factor of other
demonstrations.  It is more of an "oh, really..." experience to realize how
much worse you are with one eye than two.

#7 (using two fingers at different distances to teach crossed vs. uncrossed
disparity) can definitely be done remotely.  It is very educational, but
again does not have the "Wow" factor.

There is also the finger "hot dog" illusion, which can be done remotely.
It is interesting, but quite different from all of the others in that
stereoscopic depth perception is not involved.

For the related phenomenon of motion parallax, "wiggle vision" is a very
nice demonstration:

Of course, depth perception from motion parallax is importantly
theoretically related to stereoscopic vision (both involve two different
images from two different views, one seen over time (and only needing one
eye)--motion parallax--and the other seen simultaneously (and requiring two
eyes)--stereovision).  But it is not the same as stereoscopic vision, so is
a separate but related issue.

For the related phenomenon of binocular disparity, there is the famous
"hole in your hand" illusion using a cardboard paper towel roll.  If
students have a spare cardboard paper towel roll, they can do this
remotely.  But, again, it is a theoretically related but separate issue.

Any other suggestions would be appreciated.

Best wishes,

Lester Loschky
Associate Director, Cognitive and Neurobiological Approaches to Plasticity
Department of Psychological Sciences
471 Bluemont Hall
1114 Mid-Campus Dr North
Kansas State University
Manhattan, KS  66506-5302
email: loschky at ksu.edu
research page: https://www.k-state.edu/psych/research/loschkylester.html
lab page: http://www.k-state.edu/psych/vcl/index.html
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