Re: any ideas? (Sophie Scott )

Subject: Re: any ideas?
From:    Sophie Scott  <sophie.scott(at)UCL.AC.UK>
Date:    Tue, 30 Dec 2003 14:48:39 +0000

It is certainly the case that pretty restricted damage to left posterior superior temporal cortex can result in 'conduction aphasia' where people can understand speech, but cannot repeat it: the converse can also occur, where people can repeat speech but not understand it (in transcortical sensory aphasia). This dissociation between repetition and comprehension has led some of us (Scott and Johnsrude, TINS 2003; Hickok and Poeppel TICS 2000; Wise et al, Brain, 2001) to suggest that (and as suggested by the work on human auditory pathways by Stephanie Clarke) early perceptual processing of speech might be mediated by (at least) two parallel pathways, one directed towards lexical semantic processing (a 'what' pathway, from the monkey literature) and one associated with the sort of sensori-motor integration necessary for repetition (a 'how' pathway). There remains some controversy about specific aspects of the anatomy underpinning this difference, which I'm not going to bore you with here. However I am intrigued as to how this dissociation, which is typically discussed as a cortical phenomenon, might relate to a hearing problem which does not appear to be centrally mediated. It would be interesting to consider the role of cortical projections from MGB (not all of which go to primary auditory cortex). best wishes Sophie >The first part does sound a little like "blindsight", where people can react >at significantly better than chance to items in the 'dead area' in cases of >hemispheric neglect (Milner and Goodale, and others). This has been ascribed >to different pathways, the 'what' and 'how' pathways, where the latter deal >with a great deal of material that never really achieves conscious >representation. >Although a lady in Lausanne (Suzanne Clarke, I think -I'm sorry, I don't >have the reference here) has being doing some work to establish evidence for >similarly parallel processing pathways in audition - under the >'what-and-where' banner, I've not heard of a 'deafhearing' equivalent to >blindsight - if such equivalence were established, it would be quite >significant for models of auditory perception! Allowing for the speculation >that such equivalent could exist, then someone reacting to an auditory >stimulus of which they can have no conscious acknowledgement is not so >strange. Unfortunately, I've never heard of blindsight (which in any case is >usually the result of particular insult to brain tissue, isn't it?) being >developed by some training regime or other, to provide a substitute for >'proper' vision. >I'd be interested to hear more on this, from anyone knowledgeable in this >area. >regards >ppl -- Sophie Scott, Wellcome RCD Fellow, Depts Psychology and Phonetics, UCL, UK. 020 7679 5342

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