In article <mike.764429677 at motion>, mike at psych.ualberta.ca (Mike Dawson)
>hucka at engin.umich.edu (Michael Hucka) writes:
>>> >2) Does anyone know of any creature that has some sort of vision system
> >but cannot sense visual motion?
>> 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.
Perhaps better stated something like "the putative human homologs of
monkey visual area MT", but of course any such claim is extremely
speculative and no doubt wrong.
> 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. For details,
>> Zihl, J., von Cramon, D., & Mai, N. (1983). Selective disturbance
> of movement vision after bilateral brain damage. Brain, 106,
>> Hess, R.H., Baker, C.L., & Zihl, J. (1989). The "motion-blind" patient:
> Low-level spatial and temporal filters. Journal of neuroscience, 9,
I hesitated to say anything about the original questions that Michael Hucka
raised, since I chauvinistically like to think that motion is truly
fundamental, not only across species but across modalities as well, but,
like Mike Mulligan and Mary Anne, never really knew if were true. I'd be
very interested if anybody has a counterexample.
Mike Dawson points out the interesting case of the motion blind patient. I
might also mention that a related animal model exists, namely strobe-reared
cats. Performance on tasks involving discrimination of directions is
severely impaired in these animals, but they have fairly normal spatial and
temporal behavior (Pasternak and Leinen, J. Neuroscience 6:938-945, 1986).
This corresponds with the normal cortical responses in such animals with
the exception of a lack of direction selectivity (Cynader and Chernenko,
Science 193:504-505, 1976).
In looking for animals that are not specialized for motion, it should be
enough to determine whether visual cells are direction selective. As
pointed out in another post, it has long been known that frogs have
numerous direction-selective retinal cells. Even in mammals, most of the
retinal ganglion cells are direction selective (although these do not
project to cortex, where direction selectivity is independently created).
Similarly, most insect eyes are full of direction selective mechanisms.
With all the direction selectivity in the world, you'd think we'd
understand how it comes about!
saul+ at pitt.edu