Dissociation of Visual Perceptions Due to Occipital Injuries, With Especial Reference to Appreciation of Movement

Riddoch, George

doi:10.1093/brain/40.1.15

Cited by 406 publications

(188 citation statements)

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“…Lesions to the homologue of primate V5/MT and surrounding areas have also been shown to cause profound de®cits in the ability to discriminate motion from dynamic noise in humans [4,23,45,60,65,66]. Visual tasks that tap the sensitivity of M-cells up to and including primary visual cortex are reported to be only slightly impaired in these same individuals [4,23].…”

Section: Introductionmentioning

confidence: 99%

Visual motion sensitivity in dyslexia: evidence for temporal and energy integration deficits

et al. 2000

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In addition to poor literacy skills, developmental dyslexia has been associated with multisensory de®cits for dynamic stimulus detection. In vision these de®cits have been suggested to result from impaired sensitivity of cells within the retino-cortical magnocellular pathway and extrastriate areas in the dorsal stream to which they project. One consequence of such selectively reduced sensitivity is a diculty in extracting motion coherence from dynamic noise, a de®cit associated with both developmental dyslexia and persons with extrastriate, dorsal stream lesions. However the precise nature of the mechanism(s) underlying these perceptual de®cits in dyslexia remain unknown. In this study, we obtained motion detection thresholds for 10 dyslexic and 10 control adults while varying the spatial and temporal parameters of the random dot kinematogram (RDK) stimuli. In Experiment 1 stimulus duration was manipulated to test whether dyslexics are speci®cally impaired for detecting short duration, rather than longer stimuli. Dot density was varied in Experiment 2 to examine whether dyslexics' reduced motion sensitivity was aected by the amount of motion energy present in the RDKs. Dyslexics were consistently less sensitive to coherent motion than controls in both experiments. Increasing stimulus duration did not improve dyslexics' performance, whereas increasing dot density did. Thus increasing motion energy assisted the dyslexics, suggesting that their motion detectors have a lower signal to noise ratio, perhaps due to spatial undersampling. 7

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Section: Introductionmentioning

confidence: 99%

Visual motion sensitivity in dyslexia: evidence for temporal and energy integration deficits

et al. 2000

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“…Of the visual capacities typically spared in blindsight, the detection and discrimination of movement is the most robust (2,16,17). Several studies have indicated that cortically blind patients are able to discriminate the direction of movement of single spots (11,(18)(19)(20) and bars (21,22), with a preference for fastermoving targets that reflects the selectively spared sensitivity to high temporal frequencies (3).…”

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confidence: 99%

Illusory motion perception in blindsight

Azzopardi

Hock

2010

Proc. Natl. Acad. Sci. U.S.A.

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Motion detection is typically spared in blindsight, which results from damage to the striate cortex (area V1) of the brain that is sufficient to eliminate conscious visual awareness and severely reduce sensitivity to luminance contrast, especially for high spatial and low temporal frequencies. Here we show that the discrimination of motion direction within cortically blind fields is not attributable to feature tracking (the detection of changes in position or shape), but is due instead to the detection of firstorder motion energy (spatiotemporal changes in luminance). The key to this finding was a version of the line motion illusion entailing reverse-phi motion in which opposing motion directions are simultaneously cued by motion energy and changes in stimulus shape. In forced-choice tests, a blindsighted test subject selected the direction cued by shape change when the stimulus was presented in his intact field, but reliably selected the direction cued by motion energy when the same stimulus was presented in his blind field, where relevant position information was either inaccessible or invalid. Motion energy has been characterized as objectless, so reliance on motion energy detection is consistent with impaired access to shape information in blindsight. The dissociation of motion direction by visual field (cortically blind vs. intact) provides evidence that two pathways from the retina to MT/V5 (the cortical area specialized for motion perception) are functionally distinct: the retinogeniculate pathway through V1 is specialized for feature-based motion perception, whereas the retinocollicular pathway, which bypasses V1, is specialized for detecting motion energy.superior colliculus | visual cortex | visual pathway | hemianopia B lindsight is a rare phenomenon caused by damage to the primary visual cortex (striate cortex, or V1) of the brain that is sufficient to eliminate conscious visual awareness (1, 2). Visual sensitivity to luminance contrast is reduced in the corresponding part of the visual field, most severely for high spatial and low temporal frequencies (3). The fact that it is not completely abolished for low spatial and high temporal frequencies accounts for many of the residual visual capacities that have been reported in blindsight, including, in forced-choice tests, the ability to detect and discriminate stimuli presented in the field defect (2, 4). Evidence obtained from monkeys with striate cortex lesions as well as from cortically blind patients suggests that these capacities are mediated by neural pathways that project from the retina to extrastriate visual cortex, which normally bypass the main visual pathway that projects from the retina to the striate cortex via the lateral geniculate nucleus (the retinogeniculate pathway) and involve the superior colliculus of the midbrain and the lateral geniculate and pulvinar nuclei of the thalamus (5-13).Blindsight is not merely normal vision without awareness. In addition to the loss of primary visual cortex, retrograde degeneration of relay neurons ...

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“…A further possibility is that moving stimuli, which are more readily detected in blindsight, lead to real phenomenal visual percepts (Riddoch, 1917;Barbur et al, 1993;Zeki and ffytche, 1998). …”

Section: Introductionmentioning

confidence: 99%

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

2012

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The nal publication is available at Springer via https://doi.org/10.1007/s00221-012-3327-x Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractBlindsight has been widely investigated and its properties documented. One property still debated and contested is the puzzling absence of phenomenal visual percepts of visual stimuli that can be detected with perfect accuracy. We investigated the possibility that phenomenal visual percepts of exogenous visual stimuli in patient GY might be induced by using transcranial direct current stimulation. High contrast and low contrast stimuli were presented as a moving grating in his blind hemifield. When left area MT/V5 was anodally stimulated during the presentation of high contrast gratings, he never reported a phenomenal percept of a moving grating but showed perfect blindsight performance. When applied along with low contrast gratings, for which accuracy was titrated to 60-70%, performance did not improve but responses were significantly faster. Cathodal stimulation had no effect. Results are explained in the framework of GY's reorganised cortical connexions and oscillatory patterns known to be involved in awareness in GY. The apparent presence of phenomenal visual percepts in earlier studies is shown to be a semantic confusion about what he means when he says that he sees in his blind field.

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Dissociation of Visual Perceptions Due to Occipital Injuries, With Especial Reference to Appreciation of Movement

Cited by 406 publications

References 4 publications

Visual motion sensitivity in dyslexia: evidence for temporal and energy integration deficits

Visual motion sensitivity in dyslexia: evidence for temporal and energy integration deficits

Illusory motion perception in blindsight

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

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