Action-blindsight in healthy subjects after transcranial magnetic stimulation

Christensen, Mark Schram; Kristiansen, Lasse; Rowe, James B.; Nielsen, Jens Bo

doi:10.1073/pnas.0705858105

Cited by 43 publications

(34 citation statements)

References 25 publications

(30 reference statements)

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“…Although both conscious and unconscious performance are impaired by V1 TMS at similar time windows, subjective YesNo judgments of stimulus presence have been found to be more strongly affected than forced-choice discrimination performance (Boyer, Harrison, & Ro, 2005;Christensen, Kristiansen, Rowe, & Nielsen, 2008;Ro, Shelton, Lee, & Chang, 2004). Moreover, forced-choice accuracy has been found to remain above chance on trials in which participants report not having consciously seen the stimulus.…”

Section: Tms-induced Blindsight: Evidence Of Conscious Effects In V1 mentioning

confidence: 90%

Why is “blindsight” blind? A new perspective on primary visual cortex, recurrent activity and visual awareness

Silvanto

2015

Consciousness and Cognition

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The neuropsychological phenomenon of blindsight has been taken to suggest that the primary visual cortex (V1) plays a unique role in visual awareness, and that extrastriate activation needs to be fed back to V1 in order for the content of that activation to be consciously perceived. The aim of this review is to evaluate this theoretical framework and to revisit its key tenets. Firstly, is blindsight truly a dissociation of awareness and visual detection? Secondly, is there sufficient evidence to rule out the possibility that the loss of awareness resulting from a V1 lesion simply reflects reduced extrastriate responsiveness, rather than a unique role of V1 in conscious experience? Evaluation of these arguments and the empirical evidence leads to the conclusion that the loss of phenomenal awareness in blindsight may not be due to feedback activity in V1 being the hallmark awareness. On the basis of existing literature, an alternative explanation of blindsight is proposed. In this view, visual awareness is a "global" cognitive function as its hallmark is the availability of information to a large number of perceptual and cognitive systems; this requires inter-areal long-range synchronous oscillatory activity. For these oscillations to arise, a specific temporal profile of neuronal activity is required, which is established through recurrent feedback activity involving V1 and the extrastriate cortex. When V1 is lesioned, the loss of recurrent activity prevents inter-areal networks on the basis of oscillatory activity. However, as limited amount of input can reach extrastriate cortex and some extrastriate neuronal selectivity is preserved, computations involving comparison of neural firing rates within a cortical area remain possible. This enables "local" read-out from specific brain regions, allowing for the detection and discrimination of basic visual attributes. Thus blindsight is blind due to lack of "global" long-range synchrony, and it functions via "local" neural readout from extrastriate areas.

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Section: Tms-induced Blindsight: Evidence Of Conscious Effects In V1 mentioning

confidence: 90%

Why is “blindsight” blind? A new perspective on primary visual cortex, recurrent activity and visual awareness

Silvanto

2015

Consciousness and Cognition

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“…A similar argument, based on comparisons between discrimination performance and levels of awareness in sighted and blind fields, was made by Larry Weiskrantz (2009) based on the results of Kentridge, Heywood, and Weiskrantz (1999). More recently, Christensen, Kristiansen, Rowe, and Nielsen (2008), and Overgaard, Fehl, Mouridsen, Bergholt, and Cleeremans (2008) have argued that the current methods for reporting visual awareness do not suffice for determining visual awareness. They conducted a series of studies using improved measures for determining visual awareness, and argued on the basis of these studies that blindsight is indeed severely degraded conscious vision.…”

Section: Introductionmentioning

confidence: 80%

“…New, more fine-grained methods have been developed for testing for visual awareness (Christensen et al, 2008;Overgaard et al, 2008). Based on prior testing on normal subjects, one team of researchers (Overgaard et al, 2008) developed a fourpoint scale, the ''Perceptual Awareness Scale'' (PAS), for testing visual awareness in blindsight.…”

Section: Feelings But No Qualiamentioning

confidence: 99%

Color experience in blindsight?

Brogaard¹

2011

Philosophical Psychology

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Blindsight, the ability to blindly discriminate wavelength and other aspects of stimuli in a blind field, sometimes occurs in people with lesions to striate (V1) cortex. There is currently no consensus on whether qualitative color information of the sort that is normally computed by double opponent cells in striate cortex is indeed computed in blindsight but doesn't reach awareness, perhaps owing to abnormal neuron responsiveness in striate or extra-striate cortical areas, or is not computed at all. The existence of primesight, the experience of colored afterimages in blindsight, has been taken to suggest that qualitative color information is computed either in pre-striate or striate cortical areas but is not broadcast to working memory. I argue here that a recent study in which color phosphenes were induced in a blindsighter using bilateral transcranial magnetic stimulation indicates that computations necessary for conscious color vision are lost in blindsight. Owing to this loss, the neural responsiveness in extrastriate cortical areas is abnormal and hence is unable to give rise to color awareness. Blindsight is thus degraded vision in which the computations necessary for conscious color vision have been lost.

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“…Based on prior testing of normal subjects, one team of researchers developed a four-point scale, the ''Perceptual Awareness Scale'' (PAS), for testing visual awareness in blindsight (Christensen, Kristiansen, Rowe, & Nielsen, 2008;Overgaard et al, 2008). Instead of the traditional yes/no strategy, they developed a so-called 'Perceptual Awareness Scale' (PAS).…”

Section: Type 2 Blindsightmentioning

confidence: 99%

Type 2 blindsight and the nature of visual experience

Brogaard

2015

Consciousness and Cognition

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Action-blindsight in healthy subjects after transcranial magnetic stimulation

Cited by 43 publications

References 25 publications

Why is “blindsight” blind? A new perspective on primary visual cortex, recurrent activity and visual awareness

Why is “blindsight” blind? A new perspective on primary visual cortex, recurrent activity and visual awareness

Color experience in blindsight?

Type 2 blindsight and the nature of visual experience

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