Re: blindsight ("Dr. Leon Deouell" )

Subject: Re: blindsight
From:    "Dr. Leon Deouell"  <deouell(at)SOCRATES.BERKELEY.EDU>
Date:    Thu, 31 May 2001 10:15:12 -0700

The closest neuropsychological condition that would meet the blindsight
hallmark of perception without awareness may be auditory neglect or
auditory extinction. Patients with neglect, usually following right
hemisphere stroke, ignore, do not respond to, and do not orient to stimuli
on the side of space opposite the side of their lesion. Although unilateral
neglect is easier to diagnose in the visual modality, it is present in all
modalities in some form, including audition. We recently had a paper in
Neuroreport, where we described a group of right hemisphere damaged
(stroke) patients suffering from auditory extinction (meaning that when
presented with two stimuli, one on the left and one on the right, they are
not aware of the stimulus on the left, i.e., contralateral to the side of
the brain lesion). The interesting point was that in some cases
(significantly above chance), the patients reported the identity of the
stimulus (a CV syllable) that was actually on the left, rather than the one
that was on the right. We took this to imply implicit processing of stimuli
of which the patient is not aware. There have been some earlier reports
that also support this possibility (you could find the references in the
paper quoted below). None of these are as dramatic and demonstrative as
seeing a patient with blindsight, and more controls are even needed to
validate our initialdata, but on the other hand, patients with neglect are
unfortunately abundant. One important neuroanatomical distinction is that
while blindsight is a consequence to primary visual area loss, neglect and
extinction may ( and frequently do) occur without primary sensory loss. In
fact, our subjects had normal pure tone audiometry in the range of 500-2000.

The reference is :

Deouell, L.Y., & Soroker, N. (2000). What is extinguished in auditory
extinction? NeuroReport, 11, 3059-3062

I am happy to send an electronic version upon request.

  Leon Deouell



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Dr. Leon Deouell, M.D., Ph.D.
University of California, Berkeley
4143 Tolman # 5050
Berkeley, CA 94720-5050

Tel: 510-6439744
Fax:510-6421196