Form completion across a hemianopic boundary: Behindsight?

McCarthy, Rosaleen A.; James-Galton, Merle; Plant, Gordon T.

doi:10.1016/j.neuropsychologia.2006.01.036

Cited by 11 publications

(8 citation statements)

References 41 publications

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“…This phenomenon can occur when a visual stimulus is presented across the vertical meridian such that it intrudes both the blind and sighted hemifield; in such circumstance, some patients are able to perceive the complete figure. First described by Poppelreuter in 1917 who studied brain-damaged soldiers during the First World War (Poppelreuter, 1917), hemianopic completion has been replicated several times in patients both with or without blindsight (McCarthy et al, 2006;Sergent, 1988;Warrington, 1965Warrington, , 1962 and the term "behindsight" (McCarthy et al, 2006) was proposed to describe this phenomenon. While some patients experience completion even when the blind field component is physically absent, it is most robust with complete stimuli which intrude both the intact and blind field (Marcel, 1998;Torjussen, 1976).…”

Section: Hemianopic Completionmentioning

confidence: 99%

“…While some patients experience completion even when the blind field component is physically absent, it is most robust with complete stimuli which intrude both the intact and blind field (Marcel, 1998;Torjussen, 1976). This phenomenon has been shown not to be related to attentional deficits or incomplete damage to V1 enabling residual conscious vision in the hemianopic field (McCarthy et al, 2006). Symmetry, regularity and simplicity are amongst the features which most effectively produce hemianopic completion.…”

Section: Hemianopic Completionmentioning

confidence: 99%

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On the “blindness” of blindsight: What is the evidence for phenomenal awareness in the absence of primary visual cortex (V1)?

2019

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Blindsight has been central to theories of phenomenal awareness; that a lesion to primary visual cortex (V1) abolishes all phenomenal awareness while unconscious visual functions can remain has led to the view that this region plays a crucial role in generating visual consciousness. However, since the early 20th century, there have been reports, many of which controversial, of phenomenal awareness in patients with V1 lesions. These reports include selective sparing of motion awareness, hemianopic completion and visual aftereffects. More recently, there have been successful attempts of inducing visual qualia with noninvasive brain stimulation. Here we critically review this evidence and discuss their implications to theoretical understanding of phenomenal awareness.

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Section: Hemianopic Completionmentioning

confidence: 99%

Section: Hemianopic Completionmentioning

confidence: 99%

On the “blindness” of blindsight: What is the evidence for phenomenal awareness in the absence of primary visual cortex (V1)?

2019

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“…Another way to demonstrate the residual capacities of HH patients in their blind visual field is to study how a stimulus presented in that field affects a stimulus presented in their normal field. Such testing has been done with tasks like filling out forms ( McCarthy et al, 2006 ). In these experiments, half of the stimulus shape is shown in the normal hemifield, and then the patient must guess the complete shape.…”

Section: Behavioral Consequences Of a Unilateral Occipital Lesionmentioning

confidence: 99%

Behavioral Consequences and Cortical Reorganization in Homonymous Hemianopia

Chokron

Perez

Peyrin

2016

Front. Syst. Neurosci.

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The most common visual defect to follow a lesion of the retrochiasmal pathways is homonymous hemianopia (HH), whereby, in each eye, patients are blind to the contralesional visual field. From a behavioral perspective, in addition to exhibiting a severe deficit in their contralesional visual field, hemianopic patients can also present implicit residual capacities, now usually referred to collectively as blindsight. It was recently demonstrated that HH patients can also suffer from a subtle deficit in their ipsilesional visual field, called sightblindness (the reverse case of blindsight). Furthermore, the nature of the visual deficit in the contralesional and ipsilesional visual fields, as well as the pattern of functional reorganization in the occipital lobe of HH patients after stroke, all appear to depend on the lesion side. In addition to their contralesional and ipsilesional visual deficits, and to their residual capacities, HH patients can also experience visual hallucinations in their blind field, the physiopathological mechanisms of which remain poorly understood. Herein we review blindsight in terms of its better-known aspects as well as its less-studied clinical signs such as sightblindness, hemispheric specialization and visual hallucinations. We also discuss the implications of recent experimental findings for rehabilitation of visual field defects in hemianopic patients.

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“…As an aside, we note that this aspect of our model may also explain the phenomenon of “ hemianopic completion ” [60], whereby some patients with hemianopia report a retinotopic completion of form when the object overlaps the vertical boundary of their field defect [60], [61], [62]. Poppelreuter [63] observed that some patients with hemianopia reported seeing an entire figure when only part of the presented form fell in the intact visual hemifield.…”

Section: Discussionmentioning

confidence: 89%

Visual Search and Line Bisection in Hemianopia: Computational Modelling of Cortical Compensatory Mechanisms and Comparison with Hemineglect

Lanyon

Barton

2013

PLoS ONE

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Hemianopia patients have lost vision from the contralateral hemifield, but make behavioural adjustments to compensate for this field loss. As a result, their visual performance and behaviour contrast with those of hemineglect patients who fail to attend to objects contralateral to their lesion. These conditions differ in their ocular fixations and perceptual judgments. During visual search, hemianopic patients make more fixations in contralesional space while hemineglect patients make fewer. During line bisection, hemianopic patients fixate the contralesional line segment more and make a small contralesional bisection error, while hemineglect patients make few contralesional fixations and a larger ipsilesional bisection error. Hence, there is an attentional failure for contralesional space in hemineglect but a compensatory adaptation to attend more to the blind side in hemianopia. A challenge for models of visual attentional processes is to show how compensation is achieved in hemianopia, and why such processes are hindered or inaccessible in hemineglect. We used a neurophysiology-derived computational model to examine possible cortical compensatory processes in simulated hemianopia from a V1 lesion and compared results with those obtained with the same processes under conditions of simulated hemineglect from a parietal lesion. A spatial compensatory bias to increase attention contralesionally replicated hemianopic scanning patterns during visual search but not during line bisection. To reproduce the latter required a second process, an extrastriate lateral connectivity facilitating form completion into the blind field: this allowed accurate placement of fixations on contralesional stimuli and reproduced fixation patterns and the contralesional bisection error of hemianopia. Neither of these two cortical compensatory processes was effective in ameliorating the ipsilesional bias in the hemineglect model. Our results replicate normal and pathological patterns of visual scanning, line bisection, and differences between hemianopia and hemineglect, and may explain why compensatory processes that counter the effects of hemianopia are ineffective in hemineglect.

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Form completion across a hemianopic boundary: Behindsight?

Cited by 11 publications

References 41 publications

On the “blindness” of blindsight: What is the evidence for phenomenal awareness in the absence of primary visual cortex (V1)?

On the “blindness” of blindsight: What is the evidence for phenomenal awareness in the absence of primary visual cortex (V1)?

Behavioral Consequences and Cortical Reorganization in Homonymous Hemianopia

Visual Search and Line Bisection in Hemianopia: Computational Modelling of Cortical Compensatory Mechanisms and Comparison with Hemineglect

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