Document Detail

Are hemianopic monkeys and a human hemianope aware of visual events in the blind field?
MedLine Citation:
PMID:  22441257     Owner:  NLM     Status:  MEDLINE    
In three hemianopic monkeys and one normal monkey who subsequently became hemianopic and in one human hemianope we measured reaction times to touch the remembered position of a brief visual target presented in the normal hemifield or in the blind hemifield, or on the blank trials where no visual target occurred and the correct response was to touch a separate and permanently outlined part of the display. This is the same procedure as first used to demonstrate blindsight in these hemianopic monkeys. In the present experiment physically salient high-contrast (0.95) grating stimuli, which we have previously shown are easily detected and localized in the blind field, were used, and the monkeys' reaction times were also measured. With rare exceptions the monkeys indicated that the visual targets in the blind field were blanks, but their otherwise identical motor responses to targets and blanks had significantly different latencies, which were longer for real targets than for blanks. The results indicate that when the monkeys detect that the stimulus has occurred but do not perceive it as a light, or are just guessing, reaction times are longer. Even when the target in the blind field was moving, it was categorized as a blank. In the human hemianope both high- and low-contrast stimuli were used, and the subject had to indicate whether he had been 'aware' or 'unaware' of the target, after making the reaching response. The latencies when he was correct and aware were significantly shorter than when he was unaware and 'just guessing'. However, he was also significantly faster to respond correctly to the blind-field target when he was unaware and correct than when he was unaware and incorrect, a difference reflected in his percentage correct scores even when totally unaware. Collectively, the results support the notion that the hemianopic monkeys, like the human hemianope, know that something has happened in the blind field as long as the stimuli are physically salient even though the stimuli are categorized as blanks, presumably because, like the human hemianope, there was no phenomenal visual percept.
Alan Cowey; Iona Alexander
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2012-03-23
Journal Detail:
Title:  Experimental brain research     Volume:  219     ISSN:  1432-1106     ISO Abbreviation:  Exp Brain Res     Publication Date:  2012 May 
Date Detail:
Created Date:  2012-04-30     Completed Date:  2012-08-29     Revised Date:  2013-12-13    
Medline Journal Info:
Nlm Unique ID:  0043312     Medline TA:  Exp Brain Res     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  47-57     Citation Subset:  IM    
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MeSH Terms
Analysis of Variance
Functional Laterality
Hemianopsia* / physiopathology,  psychology,  veterinary
Macaca mulatta
Middle Aged
Photic Stimulation
Psychomotor Performance / physiology*
Visual Fields / physiology*
Visual Perception / physiology*
Grant Support
G971/397B//Medical Research Council

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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