Whooa, whoa, whoa!
Too much confusion for one posting!
One confusion on top of another, but two wrongs don't make a right!
Where to begin? In the middle, I guess. I'll interpolate comments.
In <7nkg7t$8qo$1 at news1.xs4all.nl> "Mervyn van Kuyen" <mervyn at xs4all.nl>
writes:
>>JoRoss wrote:
>>1 - Blindsight. I read a paragraph about this, and it looks like an
>interesting
>>hook for a story I'm working on. But I don't know: what causes it
(stroke,
>>brain lesion--if there is such a thing--head trauma, etc.), if it can
occur
>in
>>the complete visual field (I read about it on one side only), and how
>people
>>who have it deal with it. If I understand blindsight (probably not),
it
>seems
>>that your subconscious (or unconscious) can see, but you cannot
consciously
>>"see" what you're seeing--you are, effectively, blind. True, false? I
don't
>>know if a low-level, speculative discussion is appropriate on this
>newsgroup
>>(please e-mail if not), but I'd love to know more.
>>>The left hemispere of the cortex deals with the right visual field,
>the right hemispere deals with both left and right.
COMMENT: the right hemisphere deals with the left visual field in
exactly the same way that the left hemisphere deals with the right
visual field, i.e. as being the cortical projection areas for left and
right visual fields, respectively. What you may be thinking of
(perhaps misunderstanding whatt you have read) is that the right
hemisphere seems to be important for "attention" in both left and right
visual fields, left and right somatosensory perception, etc.
There damage to
>the left hemispere has no blinding effect, language could be impaired.
COMMENT: strictly speaking, it would have to be a pretty large or very
precisely placed lesion in EITHER hemisphere to have a "blinding"
effect--and the "blinding" would be only in one visual field. For
example, one of my patients who (relevant to the question of face
perception, discussed under a different heading) had prosopagnosia on
the basis of PERHAPS a unilateral lesion, was "blind in the upper part
of her left visual field, i.e. a field cut in the "left upper
quadrant".
>When the right hemisphere is damaged (through a stroke), then the
patient
>neglects his right half of the world and body. He/she might eat only
the
>left side of the plate or put make-up on the left side only.
CCOMMENT: I'll give you the benefit of the doubt and assume that you
really do know what you meant to say here, but suffer from left/right
confusion or just get mixed up when you try to use words. The
unilateral neglect due to a right hemisphere lesion (usually in the
parietal lobe; "vision" is really not affected att all) is, of course,
the exact OPPOSITE of what you have written here. (Yes, I'm sure.
I've presented several papers on my own research in unilateral
neglect.)
GENERAL COMMENT: a wise person knows what he knows and knows what he
does not know. That is, he knows where his knowledge ends and his
speculations begin. To avoid misleading others, who are admittedly
ignorant and are seeking information, one should state up-front what it
is you know for sure, what it is you THINK you know (becauuse you read
it or heard it somewhere), and what is just a sheer "guess". This
proper display of intellectual honesty and humility (which I have found
to be standard practice in the very best neuroscientists of our day)
has the further advantage of protecting you from sometimes very harsh
criticism and contempt.
HISTORICAL NOTE: "Blindsight" is the phenomenon of people with
cortical blindness (i.e. large lesions in just exactly the right spot,
the visual cortex causing a complete loss of conscious awareness of any
visual stimuli) being able to point to objects they are blindly
"looking" at (i.e. directing their eyes towards) more reliably than one
could expect if they were just pointing randomly. Larry Weizkrantz
(have I mis-spelled his name? dosn't look right to me) was one of the
first (THE first?) to study this systematically. I had the privilege
of hearing his first-hand report, very early in this exploration, when
Hans-Lukas Teuber invited him to speak to our class (I studied with him
c. 1960-1961).
Teuber had a grading policy which is relevant to the advice I gave you.
He said that, eventually, many of us would be teaching, i.e. be in a
position where people trusted us to tell them things which were true.
Therefore, in an effort to develop habits of intellectual honesty and
humility in us, he would give us one point for each correct answer on
one of his exams, zero if we left the item blank or said "I don't
know", but MINUS one point if we wrote something which was not correct.
ANOTHER PERSONAL HISTORICAL NOTE: Last November, Elizabeth Warrington
came from London to speak at the NY Academy of Sciences (at my
invitation). I've known her, casually, for many years, but it wasn't
ujtil I ws going over her bibliography (to prepare to introduce her)
that I realized that she had collaborated with Weiskrantz in some of
those very early blindsight studies!
F. Frank LeFever, Ph.D.
New York Neuropsychology Group
