Literature DB >> 22441257

Are hemianopic monkeys and a human hemianope aware of visual events in the blind field?

Alan Cowey1, Iona Alexander.   

Abstract

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.

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Year:  2012        PMID: 22441257     DOI: 10.1007/s00221-012-3066-z

Source DB:  PubMed          Journal:  Exp Brain Res        ISSN: 0014-4819            Impact factor:   1.972


  26 in total

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Journal:  Neuropsychologia       Date:  2007-12-08       Impact factor: 3.139

6.  Perceiving electrical stimulation of identified human visual areas.

Authors:  Dona K Murphey; John H R Maunsell; Michael S Beauchamp; Daniel Yoshor
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8.  Leter: Residual visual function after brain wounds involving the central visual pathways in man.

Authors:  E Poppel; R Held; D Frost
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9.  Conscious visual perception without V1.

Authors:  J L Barbur; J D Watson; R S Frackowiak; S Zeki
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10.  Residual colour vision in a human hemianope: spectral responses and colour discrimination.

Authors:  P J Brent; C Kennard; K H Ruddock
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  2 in total

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Authors:  Tim Martin; Anasuya Das; Krystel R Huxlin
Journal:  Brain       Date:  2012-11       Impact factor: 13.501

2.  Modulation of cortical excitability can speed up blindsight but not improve it.

Authors:  Alan Cowey; Iona Alexander; Amanda Ellison
Journal:  Exp Brain Res       Date:  2012-11-15       Impact factor: 1.972

  2 in total

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