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[Q] Visual detection of moving vs. stationary stimuli

Michael Hucka hucka at engin.umich.edu
Sun Mar 27 12:19:36 EST 1994


  anderson> mike at psych.ualberta.ca (Mike Dawson) writes:

  >> I do not know of any *normal* creature of this sort.  However, there
  >> is a very famous clinical case, the so-called "motion blind patient".
  >> This woman has suffered damage to visual system MT from a stroke.
  >> Her ability to see static objects is unaffected, as measured by a
  >> large number of standard psychophysical techniques.  However, her
  >> ability to see movement has almost been totally erased.  

  anderson> This has always struck me as very weird.  What does she see
  anderson> instead of motion?  Nothing?  Or a series of "still images"?
  anderson> (But wouldn't this "look" like motion?)  Or what?

Semir Zeki, in his 1993 book _A_Vision_of_the_Brain_, writes the following
about Zihl's patient:

  [The damage] had led to several problems, including a difficulty with
  calculations and a mild aphasia.  But the most striking observation by far
  was the patient's inability to see objects in motion.  So severe was this
  that, 'She had difficulty, for example, in pouring tea or coffee into a cup
  because the fluid appeared to be frozen, like a glacier.  In addition, she
  could not stop pouring at the right time since she was unable to perceive
  the movement in the cup (or a pot) when the fluid rose.  The patient also
  complained of difficulties in following a dialogue because she could not
  see the movements of ... the mouth of the speaker'.  She had difficulty in
  crossing roads because of the cars whose exact position was difficult for
  her to judge -- 'When I'm looking at the car first, it seems far away.  But
  then, when I want to cross the road, suddenly the car is very near' -- she
  could not see the position of the car in between.  In brief, she had no
  knowledge of visual movement and little knowledge of the visual world when
  it was set in motion. [p. 82]

So I interpret this as meaning she saw the world as a series of still images.
Perhaps sort of like being in a place where the only light is a strobelight.
--
-- Mike Hucka
   University of Michigan, Ann Arbor, Mich.



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