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 ----------------------------------------------------------------------------------------------------------- Dr. Leon Deouell, M.D., Ph.D. University of California, Berkeley 4143 Tolman # 5050 Berkeley, CA 94720-5050 Tel: 510-6439744 Fax:510-6421196

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