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Glyn W. Humphreys - One of the best experts on this subject based on the ideXlab platform.
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Impaired texture segregation but spared contour integration following damage to right posterior parietal cortex
Experimental Brain Research, 2013Co-Authors: Kathleen Vancleef, Johan Wagemans, Glyn W. HumphreysAbstract:We examined the relations between texture segregation and contour integration in patients with deficits in spatial attention leading to left or right hemisphere extinction. Patients and control participants were presented with texture and contour stimuli consisting of oriented elements. We induced regularity in the stimuli by manipulating the element orientations resulting in an implicit texture border or explicit contour. Participants had to discriminate curved from straight shapes without making eye movements, while the stimulus presentation time was varied using a QUEST procedure. The results showed that only patients with right hemisphere extinction had a spatial bias, needing a longer presentation time to determine the shape of the border or contour on the Contralesional Side, especially for borders defined by texture. These results indicate that texture segregation is modulated by attention-related brain areas in the right posterior parietal cortex.
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Neuropsychological evidence for an interaction between endogenous visual and motor-based attention
Neurocase, 2011Co-Authors: Keiko Kitadono, Glyn W. HumphreysAbstract:We report data examining the relations between endogenous allocation of visual attention and effects of motor-preparation on attention. We tested a patient with a spatial bias in perceptual report following damage to the left inferior parietal lobe and superior temporal gyrus. Previously we have shown that the spatial bias in report can be reduced when a movement is planned to where a target falls in the Contralesional field, while the bias is exacerbated when a movement is planned to the ipsilesional Side (Kitadono & Humphreys, 2007, Cognitive Neuropsychology, 24). Here we pitted the effects of planning a movement to the contra- or ipsilesional Side against the effects of endogenous visual attention, manipulated by varying the probability of where a target would fall. In a no-movement baseline, there was better identification of Contralesional targets when there was a good likelihood of targets appearing on the Contralesional Side (the 20–80 and 50–50 conditions) compared with when targets had a low prob...
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Sustained interactions between perception and action in visual extinction and neglect: evidence from sequential pointing.
Neuropsychologia, 2008Co-Authors: Keiko Kitadono, Glyn W. HumphreysAbstract:Interactions between perception and action were examined by assessing the effects of action programming on extinction and neglect. In an extension of prior work, effects of sequential motor programming were assessed under conditions in which attention was first directed to an ipsilesional stimulus. Despite pointing and reporting a stimulus on the ipsilesional Side first, programming a second action to the Contralesional Side reduced the spatial deficit on report, improving the report of Contralesional stimuli (relative to when the patient just pointed to the ipsilesional Side) while decreasing the report of ipsilesional items. The data suggest that perception and action interact through motor feedback to early visual coding, helping a patient overcome a lack of visual awareness to Contralesional stimuli. This is effective even when attention has to be disengaged from the ipsilesional Side suggesting that motor programming decreases ipsilesional capture and exerts a sustained influence on perception.
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short term effects of the rubber hand illusion on aspects of visual neglect
Neurocase, 2007Co-Authors: Keiko Kitadono, Glyn W. HumphreysAbstract:The ‘rubber hand’ illusion was induced in a patient showing unilateral visual neglect, with the patient experiencing a shift in the felt position of his right hand towards a Contralesional rubber hand. Immediately following the illusion, there were short-lasting reductions in neglect for bisecting about the midline and for cancelling multiple stimuli. No effects were found on the ability to encode briefly presented visual stimuli on the Contralesional Side. The data demonstrate that the illusion can temporarily alter some aspects of neglect, without altering basic visual encoding. The underlying mechanisms, and the relations to other rehabilitation procedures, are discussed.
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A deficit in Contralesional object representation associated with attentional limitations after parietal damage
Cognitive neuropsychology, 2006Co-Authors: Marie-pierre Vernier, Glyn W. HumphreysAbstract:Stankiewicz, Hummel, and Cooper (1998) proposed that detailed coding of part-whole relations for objects is contingent on objects being attended. We report a neuropsychological test of this assertion. We examined the effects of left-right reflection on object matching in a group of patients with parietal damage and impaired attention to the Contralesional Side of space (Experiment 1). The patients were poor at matching objects subject to left-right reflection, relative to identical stimuli (Experiment 2). This was not due to a lack of sensitivity to information on the Contralesional Side. In a subsequent study, the patients were better at matching identical whole objects at fixation than when they just received half the object in their ipsilesional field (Experiment 3). However, unlike both nonlesioned controls and control patients with frontal lesions, the parietal patients were unaffected by altering the relative spatial locations of object features in their Contralesional field (Experiment 4). The basic result, of poor performance with left-right-reflected items, was also replicated using a priming rather than an explicit matching procedure (Experiment 5). These results provide confirmation that visual attention, mediated by the posterior parietal cortex, is important for generating part-whole codes that facilitate the matching of mirror-reflected objects.
Hans-otto Karnath - One of the best experts on this subject based on the ideXlab platform.
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“Nonspatial” Attentional Deficits Interact with Spatial Position in Neglect
Journal of cognitive neuroscience, 2017Co-Authors: Chris Rorden, Hans-otto KarnathAbstract:A widely debated question concerns whether or not spatial and nonspatial components of visual attention interact in attentional performance. Spatial neglect is a common consequence of brain injury where individuals fail to respond to stimuli presented on their Contralesional Side. It has been argued that, beyond the spatial bias, these individuals also tend to exhibit nonspatial perceptual deficits. Here we demonstrate that the "nonspatial" deficits affecting the temporal dynamics of attentional deployment are in fact modulated by spatial position. Specifically, we observed that the pathological attentional blink of chronic neglect is enhanced when stimuli are presented on the Contralesional Side of the trunk while keeping retinal and head-centered coordinates constant. We did not find this pattern in right brain-damaged patients without neglect or in patients who had recovered from neglect. Our work suggests that the nonspatial attentional deficits observed in neglect are heavily modulated by egocentric spatial position. This provides strong evidence against models that suggest independent modules for spatial and nonspatial attentional functions while also providing strong evidence that trunk position plays an important role in neglect.
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Allocentric neglect strongly associated with egocentric neglect.
Neuropsychologia, 2012Co-Authors: Chris Rorden, Haukur Hjaltason, Paul Fillmore, Julius Fridriksson, Olafur Kjartansson, Sigridur Magnusdottir, Hans-otto KarnathAbstract:Following brain injury, many patients experience egocentric spatial neglect, where they fail to respond to stimuli on the Contralesional Side of their body. On the other hand, allocentric, object-based neglect refers to the symptom of ignoring the Contralesional Side of objects, regardless of the objects' egocentric position. There is an established tradition for conSidering these two phenomena as both behaviorally and anatomically dissociable. However, several studies and some theoretical work have suggested that these rather reflect two aspects of a unitary underlying disorder. Furthermore, in a recent large study Yue et al. [Archives of Physical Medicine and Rehabilitation 93 (2012) 156] reported that acute allocentric neglect is only observed in cases where substantial egocentric neglect is also present. In a new sample of right hemisphere stroke patients, we attempted to control for potential confounds by using a novel continuous measure for allocentric neglect (in addition to a recently developed continuous measure for egocentric neglect). Our findings suggest a strong association between egocentric and allocentric neglect. Consistent with the work of Yue et al. (2012), we found allocentric behavioral deficits only in conjunction with egocentric deficits as well as a large corresponding overlap for the anatomical regions associated with egocentric and with allocentric neglect. We discuss how different anatomical and behavioral findings can be explained in a unified physiologically plausible framework, whereby allocentric and egocentric effects interact.
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Object-based neglect varies with egocentric position
Journal of cognitive neuroscience, 2011Co-Authors: Hans-otto Karnath, André Mandler, Simon ClavagnierAbstract:Different reference frames have been identified to influence neglect behavior. In particular, neglect has been demonstrated to be related to the Contralesional Side of the subject's body (egocentric reference frames) as well as to the Contralesional Side of individual objects irrespective of their position to the patient (object-based reference frame). There has been discussion whether this distinction separates neglect into body-and object-based forms. The present experiment aimed to prove possible interactions between object-based and egocentric aspects in spatial neglect. Neglect patients' eye and head movements were recorded while they explored objects at five egocentric positions along the horizontal dimension of space. The patients showed both egocentric as well as object-based behavior. Most interestingly, data analysis revealed that object-based neglect varied with egocentric position. Although the neglect of the objects' left Side was strong at Contralesional egocentric positions, it ameliorated at more ipsilesional egocentric positions of the objects. The patients showed steep, ramp-shaped patterns of exploration for objects located on the far Contralesional Side and a broadening of these patterns as the locations of the objects shifted more to the ipsilesional Side. The data fitted well with the saliency curves predicted by a model of space representation, which suggests that visual input is represented in two modes simultaneously: in veridical egocentric coordinates and in within-object coordinates.
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Transcutaneous electrical stimulation and vibration of neck muscles in neglect
Experimental brain research, 1995Co-Authors: Hans-otto KarnathAbstract:Four neglect patients without visual field defects, one with a lesion of the right basal ganglia and three with a right, predominantly parietal lesion, were examined with a cancellation and a copying task before, during and after neck muscle vibration, during transcutaneous electrical stimulation of neck muscles and during vibration of hand muscles on the left Side. In all patients, neck muscle vibration improved task performance, while transcutaneous electrical stimulation and hand vibration had little or no effect. The present results demonstrate that the effect of neck muscle vibration cannot be explained as arousal and activation due to unspecific sensory stimulation on the Contralesional Side of the body. They rather argue for the assumption that the compensatory effect of neck muscle vibration on neglect is an effect induced by the predominant activation of afferent Ia nerve fibres and their specific contribution to the central representation of egocentric space.
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Disturbed coordinate transformation in the neural representation of space as the crucial mechanism leading to neglect
Neuropsychological Rehabilitation, 1994Co-Authors: Hans-otto KarnathAbstract:Abstract Karnath (1988) and Gainotti, D'Erme and De Bonis (1989). suggested that the typical and severe neglect symptomology that is seen predominantly after lesions of the right hemisphere, is due to the combined effect of at least two different components: (1) an imbalance of lateral orienting tendencies with spontaneously primary orienting towards the ipsilesional Side; together with (2) a deficit in orienting attention (from this primary focus), as well as eye or limb movements, to the Contralesional Side of the sagittal midplane.
M. Jane Riddoch - One of the best experts on this subject based on the ideXlab platform.
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Functional electrical stimulation (FES) of the upper limb alleviates unilateral neglect: a case series analysis.
Neuropsychological rehabilitation, 2009Co-Authors: Peter Harding, M. Jane RiddochAbstract:We report the results of a new form of therapy for unilateral spatial neglect. Functional electrical stimulation (FES) applied to the left forearm extensor muscles reduced the symptoms of severe left unilateral visual neglect in three patients, with the benefits being measurable at 6 months post-treatment. We suggest that FES activates a proprioceptive map within the right parietal lobe whose level of activation is otherwise diminished by the lesion. This both increases awareness of the Contralesional Side and stimulates functional interactions with the environment.
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Long-term effects of prism adaptation in chronic visual neglect: A single case study
Cognitive neuropsychology, 2006Co-Authors: Glyn W. Humphreys, Alexia Watelet, M. Jane RiddochAbstract:We investigated the effects of long-term training using prism adaptation on a patient with chronic neglect. A positive effect of prism adaptation was apparent on tests of visuo-spatial processing (cancellation, bisection, and grasping), but there was no benefit for neglect on the detection of errors on the Contralesional Side of words or on the detection the left Side of chimeric faces. Across training sessions, the benefit of adaptation on immediate performance decreased, but it increased across sessions and within sessions when performance was tested up to 90 minutes after adaptation. The beneficial effect was maintained up to 1 year posttraining. In later sessions there were also increased negative after-effects following prism adaptation, as training progressed. There was no improvement on tests of mathematical cognition, which comprised an independent deficit in this patient. The data suggest that prolonged prism training can induce long-term adaptive spatial realignment of visuomotor mappings, ameliorating some aspects of neglect. We discuss the implications for the rehabilitation of neglect and for understanding the neglect syndrome more generally.
Anouk Lamontagne - One of the best experts on this subject based on the ideXlab platform.
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Exploring barriers and facilitators to the clinical use of virtual reality for post-stroke unilateral spatial neglect assessment.
Disability and rehabilitation, 2017Co-Authors: Tatiana Ogourtsova, Philippe S. Archambault, Anouk LamontagneAbstract:AbstractBackground: Hemineglect, defined as a failure to attend to the Contralesional Side of space, is a prevalent and disabling post-stroke deficit. Conventional hemineglect assessments lack sens...
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Perceptual and locomotor factors affect obstacle avoidance in persons with visuospatial neglect
Journal of NeuroEngineering and Rehabilitation, 2014Co-Authors: Gayatri Aravind, Anouk LamontagneAbstract:BackgroundFor safe ambulation in the community, detection and avoidance of static and moving obstacles is necessary. Such abilities may be compromised by the presence of visuospatial neglect (VSN), especially when the obstacles are present in the neglected, i.e. Contralesional field.MethodsTwelve participants with VSN were tested in a virtual environment (VE) for their ability to a) detect moving obstacles (perceptuo-motor task) using a joystick with their non-paretic hand, and b) avoid collision (locomotor task) with moving obstacles while walking in the VE. The responses of the participants to obstacles approaching on the Contralesional Side and from head-on were compared to those during ipsilesional approaches.ResultsUp to 67 percent of participants (8 out of 12) collided with either Contralesional or head-on obstacles or both. Delay in detection (perceptuo-motor task) and execution of avoidance strategies, and smaller distances from obstacles (locomotor task) were observed for colliders compared to non-colliders. Participants’ performance on the locomotor task was not explained by clinical measures of VSN but slower walkers displayed fewer collisions.ConclusionPersons with VSN are at the risk of colliding with dynamic obstacles approaching from the Contralesional Side and from head-on. Locomotor-specific assessments of navigational abilities are needed to appreciate the recovery achieved or challenges faced by persons with VSN.
Giuseppe Vallar - One of the best experts on this subject based on the ideXlab platform.
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Somatoparaphrenia: a body delusion. A review of the neuropsychological literature
Experimental Brain Research, 2009Co-Authors: Giuseppe Vallar, Roberta RonchiAbstract:A review of published brain-damaged patients showing delusional beliefs concerning the Contralesional Side of the body (somatoparaphrenia) is presented. Somatoparaphrenia has been reported, with a few exceptions, in right-brain-damaged patients, with motor and somatosensory deficits, and the syndrome of unilateral spatial neglect. Somatoparaphrenia, most often characterized by a delusion of disownership of left-Sided body parts, may however occur without associated anosognosia for motor deficits, and personal neglect. Also somatosensory deficits may not be a core pathological mechanism of somatoparaphrenia, and visual field disorders may be absent. Deficits of proprioception, however, may play a relevant role. Somatoparaphrenia is often brought about by extensive right-Sided lesions, but patients with posterior (parietal-temporal), and insular damage are on record, as well as a few patients with subcortical lesions. Possible pathological factors include a deranged representation of the body concerned with ownership, mainly right-hemisphere-based, and deficits of multisensory integration. Finally, the rubber hand illusion, that brings about a bodily misattribution in neurologically unimpaired participants, as somatoparaphrenia does in brain-damaged patients, is briefly discussed.
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Modulation of neglect hemianesthesia by transcutaneous electrical stimulation.
Journal of the International Neuropsychological Society : JINS, 1996Co-Authors: Giuseppe Vallar, Maria Luisa Rusconi, Bruno BernardiniAbstract:The effects of transcutaneous electrical stimulation on deficits of tactile perception contralateral to a hemispheric lesion were investigated in 10 right brain-damaged patients and in four left brain-damaged patients. The somatosensory deficit recovered, transiently and in part, after stimulation of the Side of the neck contralateral to the Side of the lesion, in all 10 patients with lesions in the right hemisphere, both with (six cases) and without (four cases) left visuo-spatial hemineglect, and in one left brain-damaged patient with right hemineglect. In three left brain-damaged patients without hemineglect, the treatment had no detectable effects. In one right brain-damaged patient, the stimulation of the Side of the neck ipsilateral to the Side of the lesion temporarily worsened the somatosensory deficit. These effects of transcutaneous electrical stimulation are similar to those of vestibular stimulation. The suggestion is made that these treatments modulate, through afferent sensory pathways, higher-order spatial representations of the body, which are pathologically distorted toward the Side of the lesion. The modulatory effect is direction-specific: the defective internal representation of the Contralesional Side may be either partly restored, improving the disorder of tactile perception, or further impoverished, worsening the deficit. The possible neural basis of this modulation is discussed.