Blindsight and Unconscious Vision: What They Teach Us about the Human Visual System

Ajina, Sara; Bridge, Holly

doi:10.1177/1073858416673817

Cited by 65 publications

(28 citation statements)

References 112 publications

(133 reference statements)

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“…The existence of residual, visually-evoked activity representing blind-field regions in the damaged V1 of CB patients has important implications, both for understanding preserved vision and designing better visual restitution strategies (Ajina and Bridge, 2016;Ajina and Kennard, 2012;Chokron et al, 2008;Das and Huxlin, 2010;Herpich et al, 2019;Morland et al, 2004;Papanikolaou et al, 2014;Perez and Chokron, 2014;Smirnakis, 2016;Wandell and Smirnakis, 2009). Although it is unclear why regions with preserved V1 activity do not mediate conscious perception without training, here we reveal the potential relevance of such preserved activity to visual restoration efforts.…”

Section: Discussionmentioning

confidence: 99%

“…One proposed recovery mechanism is that training stimulates and improves visual processing in extrageniculostriate pathways mediating blindsight (Ajina and Kennard, 2012;Chokron et al, 2008;Das and Huxlin, 2010;Perez and Chokron, 2014;Smirnakis, 2016). Both human and non-human primates with V1 lesions exhibit visually-guided perceptual abilities within their blind field, despite lacking awareness (Ajina and Bridge, 2016;Leopold, 2012;Weiskrantz et al, 1974). Because blindsight is elicited by large stimuli with high-temporal and low-spatial frequency content, it is thought to rely mainly on direct geniculo-hMT+ and superior colliculus-pulvinar-extrastriate projections (Ajina and Bridge, 2016;Ajina and Kennard, 2012;Ajina et al, 2015;Bridge et al, 2008;Leopold, 2012;Schmid et al, 2010;Weiskrantz et al, 1974).…”

mentioning

confidence: 99%

“…Both human and non-human primates with V1 lesions exhibit visually-guided perceptual abilities within their blind field, despite lacking awareness (Ajina and Bridge, 2016;Leopold, 2012;Weiskrantz et al, 1974). Because blindsight is elicited by large stimuli with high-temporal and low-spatial frequency content, it is thought to rely mainly on direct geniculo-hMT+ and superior colliculus-pulvinar-extrastriate projections (Ajina and Bridge, 2016;Ajina and Kennard, 2012;Ajina et al, 2015;Bridge et al, 2008;Leopold, 2012;Schmid et al, 2010;Weiskrantz et al, 1974). Accordingly, some rehabilitation approaches have targeted blindsight to help CB patients recruit these unconscious processes, with some evidence of increased visual performance and awareness post-training (Chokron et al, 2008;Melnick et al, 2016b;Perez and Chokron, 2014;Sahraie et al, 2010;Sahraie et al, 2006).…”

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confidence: 99%

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Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

Barbot

Das

Melnick

et al. 2020

Preprint

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Damage to the primary visual cortex (V1) causes profound, homonymous visual-field loss termed cortical blindness (CB). Though long considered intractable, multiple studies now show that perceptual training can recover visual functions in chronic CB. A popular hypothesis is that training recruits intact extrageniculostriate pathways. Alternatively, training may induce plastic changes within spared regions of the damaged V1. Here, we linked changes in luminance detection sensitivity with retinotopic fMRI activity in eleven chronic CB patients, before and after extensive visual discrimination training. Our results show that the strength of spared V1 activity representing perimetrically blind-field locations before training predicts the amount of training-induced recovery of luminance detection sensitivity. Additionally, training caused an enlargement of population receptive fields in perilesional V1 cortex, which increased blind-field coverage. These findings uncover fundamental changes in perilesional V1 cortex underlying training-induced restoration of conscious luminance detection sensitivity in cortically-blind patients.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

Barbot

Das

Melnick

et al. 2020

Preprint

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“…In chronic CB, it has been hypothesized that training-induced restoration of visual motion capacities could be mediated by "alternative" visual pathways, such as those claimed to mediate "blindsight", that proceed from the retina to the dorsal lateral geniculate nucleus (dLGN) of the thalamus, the superior colliculus, pulvinar and thence to MT and other extrastriate areas (39)(40)(41)(42).…”

Section: Substrates Of Preserved Vision and Mechanisms Of Vision Restmentioning

confidence: 99%

Time is vision: functional preservation and enhanced capacity for recovery in subacute occipital stroke

Saionz

Tadin

Melnick

et al. 2019

Preprint

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One Sentence Summary: The first 3 months after an occipital stroke are characterized by a gradual -not sudden -loss of visual perceptual abilities and increased rehabilitative potential if visual discrimination training is administered in the blind field. Abstract:Stroke damage to the primary visual cortex (V1) causes a loss of vision known as hemianopia or cortically-induced blindness (CB). While early, spontaneous, perimetric improvements can occur, by 6 months post-stroke, the deficit is considered chronic and permanent. Despite evidence from sensorimotor stroke showing that early injury responses heighten neuroplastic potential, to date, rehabilitation research has focused only on chronic CB patients. Consequently, little is known about the functional properties of subacute, post-stroke visual systems, and whether they can be harnessed to enhance visual recovery. Here, for the first time, we show that conscious visual discrimination abilities are partially preserved inside subacute, perimetrically-defined blind fields, disappearing by 6 months post-stroke. Complementing this discovery, we show that global motion discrimination training initiated subacutely leads to comparable magnitude of recovery as that initiated in chronic CB. However, it does so 6 times faster, generalizes to deeper, untrained regions of the blind field, and to other [untrained] aspects of motion perception, preventing their degradation upon reaching the chronic period. Untrained subacutes exhibited only spontaneous improvements in perimetry -spontaneous recovery of motion discriminations was never observed.Thus, in CB, the early post-stroke period appears characterized by gradual -rather than suddenloss of visual processing. Subacute training stops this degradation, and is dramatically more efficient at eliciting recovery than identical training in the chronic period. Finally, spontaneous improvements in subacutes appear restricted to luminance detection, whereas recovering discrimination abilities requires deliberate training. Simply stated, after an occipital stroke, "time is VISION".

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“…Since the geniculo‐striate pathway is not functional in patients with V1 damage, there must be an alternative route by which visual information can travel to the brain to facilitate blindsight . Recent work has provided evidence that a pathway between the lateral geniculate nucleus (LGN) and motion area hMT+ may underlie these abilities . Specifically, it has been shown that such a pathway is consistently present in patients who show blindsight, but not those without blindsight …”

Section: Introductionmentioning

confidence: 99%

Visual training in hemianopia alters neural activity in the absence of behavioural improvement: a pilot study

Larcombe

Kulyomina

Antonova

et al. 2018

Ophthalmic Physiologic Optic

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BackgroundDamage to the primary visual cortex (V1) due to stroke often results in permanent loss of sight affecting one side of the visual field (homonymous hemianopia). Some rehabilitation approaches have shown improvement in visual performance in the blind region, but require a significant time investment.MethodsSeven patients with cortical damage performed 400 trials of a motion direction discrimination task daily for 5 days. Three patients received anodal transcranial direct current stimulation (tDCS) during training, three received sham stimulation and one had no stimulation. Each patient had an assessment of visual performance and a functional magnetic resonance imaging (fMRI) scan before and after training to measure changes in visual performance and cortical activity.ResultsNo patients showed improvement in visual function due to the training protocol, and application of tDCS had no effect on visual performance. However, following training, the neural response in motion area hMT+ to a moving stimulus was altered. When the stimulus was presented to the sighted hemifield, activity decreased in hMT+ of the damaged hemisphere. There was no change in hMT+ response when the stimulus was presented to the impaired hemifield. There was a decrease in activity in the inferior precuneus after training when the stimulus was presented to either the impaired or sighted hemifield. Preliminary analysis of tDCS data suggested that anodal tDCS interacted with the delivered training, modulating the neural response in hMT+ in the healthy side of the brain.ConclusionTraining can affect the neural responses in hMT+ even in the absence of change in visual performance.

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Blindsight and Unconscious Vision: What They Teach Us about the Human Visual System

Cited by 65 publications

References 112 publications

Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

Time is vision: functional preservation and enhanced capacity for recovery in subacute occipital stroke

Visual training in hemianopia alters neural activity in the absence of behavioural improvement: a pilot study

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