August 2009
Volume 9, Issue 8
Free
Vision Sciences Society Annual Meeting Abstract  |   August 2009
Dissociation of feature-based motion and ‘objectless’ motion energy for direction discrimination within the sighted and blindsighted visual fields of a hemianope
Author Affiliations
  • Paul Azzopardi
    Department of Experimental Psychology, University of Oxford, U.K.
  • Howard S. Hock
    Department of Psychology, Florida Atlantic University, U.S.A.
Journal of Vision August 2009, Vol.9, 761. doi:10.1167/9.8.761
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      Paul Azzopardi, Howard S. Hock; Dissociation of feature-based motion and ‘objectless’ motion energy for direction discrimination within the sighted and blindsighted visual fields of a hemianope. Journal of Vision 2009;9(8):761. doi: 10.1167/9.8.761.

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Abstract

The detection of motion direction is one of the visual capabilities spared by damage to the striate cortex (or pathways leading to the striate cortex) that is sufficient to eliminate conscious awareness. We have found that the discrimination of motion direction within such a cortically blind visual field is not attributable to the detection of changes in position (i.e., feature tracking), as proposed by Azzopardi and Cowey (2001), but is due instead to the detection of 1st-order motion energy (spatiotemporal changes in luminance). The experiments demonstrating this were based on a version of the line motion illusion (Hikosaka, Miyauchi & Shimojo 1993) entailing reverse-phi motion (Anstis & Rogers1975). Opposing motion directions were simultaneously cued by changes in motion energy and changes in stimulus shape. In forced-choice tests, our blindsighted test subject always selected the motion direction cued by shape when the stimulus was presented in his intact field, and reliably selected the motion direction cued by motion energy when the stimulus was presented in his cortically blind field, where it also was shown that relevant position information either was inaccessible or invalid. The dissociation of motion direction by visual field (cortically blind vs. intact) provides evidence for parallel neural pathways to cortical Area MT/V5, a brain area specialized for the perception of motion: A motion energy pathway originating in the superior colliculus and bypassing Area V1 that is not affected by striatal damage, and an object motion pathway originating in the lateral geniculate nucleus and passing through Area V1 before projecting onto Area MT. Motion energy has been characterized as ‘objectless’ by Sperling and Lu (1998), so its detection is consistent with the severely impaired access to shape information in blindsight.

Azzopardi, P. Hock, H. S. (2009). Dissociation of feature-based motion and ‘objectless’ motion energy for direction discrimination within the sighted and blindsighted visual fields of a hemianope [Abstract]. Journal of Vision, 9(8):761, 761a, http://journalofvision.org/9/8/761/, doi:10.1167/9.8.761. [CrossRef]
Footnotes
 Funded by a European Network Grant from the Oxford McDonnell Network for Cognitive Neuroscience to PA.
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