Looking at human eyes affects contralesional stimulus processing after right hemispheric stroke

Homonymous hemianopsia versus unilateral spatial neglect rehabilitation strategies in stroke patients

Abstract Visual rehabilitation therapy is one of the most problematic issue in stroke rehabilitation. The difficulties consist in specific assessment of visual deficit and poor results reports by the authors of the clinical studies. Opposite, experimental studies reports encouraging results that give hopes in this specific rehabilitation therapy. There are still difficult to analyze different aquisitions concerning various visual residual deficits after stroke, the main rehabilitation targgets being motor rehabilitation in order to ensure at least a partial autonomy in day by day life. All the studies that proved there are chances for a better quality of life if there is an improvement of visual abilities together with motor and cognitive skills with a better rehabilitation prognosis. The aim of this paper is to make a brief report regarding two of the most important visual deficits after stroke as are homonymous hemianopsia and neglect. Starting with differential diagnosis, neuroplasticity and specific rehabilitation available method, the main issues are discussed. a better understanding of phenomena that are associated with spontaneous rehabilitation, or enhancing the progress of recuperation by various method, could be able to bring a new light and hopefully better results in rehabilitation for these patients Key words: stroke, visual impairment, visual rehabilitation, neuroplasticity, homonymous hemianopsia,

Direct Gaze Partially Overcomes Hemispatial Neglect and Captures Spatial Attention

Direct gaze has been shown to be a particularly important social cue, being preferentially processed even when unconsciously perceived. Results from several visual search tasks further suggest that direct gaze modulates attention, showing a faster orientation to faces perceived as looking toward us. The present study aimed to analyze putative modulation of spatial attention by eye gaze direction in patients with unilateral neglect. Eight right hemisphere stroke patients with neglect performed a target cancelation paradigm. Patients were instructed to cross all open-eyed pictures amidst closed eyed distractors. Target images were either in direct or averted gaze. Participants performed significantly better when observing targets with direct gaze supporting the hypothesis that this gaze direction captures attention. These findings further suggest that perception of direct gaze is able to diminish the visuospatial impairment seen in neglect patients.

Unveiling residual, spontaneous recovery from subtle hemispatial neglect three years after stroke

A common and disabling consequence of stroke is the difficulty in processing contralesional space (i.e., hemispatial neglect). According to paper-and-pencil tests, neglect remits or stabilizes in severity within a few months after a brain injury. This arbitrary temporal limit, however, is at odds with neglect’s well-known dependency on task-sensitivity. The present study tested the hypothesis that the putative early resolution of neglect might be due to the insensitivity of testing methods rather than to the lack of spontaneous recovery at later stages. A right hemisphere stroke patient was studied longitudinally for 3 years. According to paper-and-pencil tests the patient showed no symptom of hemispatial neglect 1 month post stroke. Awareness of spatially lateralized visual targets was then assessed by means of computer-based single- and dual-tasks requiring an additional top-down deployment of attention for the parallel processing of visual or auditory stimuli. Errorless performance at computer-based tasks was reached at month 12 and maintained until month 29 after stroke. A bottom-up manipulation was then implemented by reducing target diameter. Following this change, more than 50% of contralesional targets were omitted, mostly under dual-tasking. At months 40 and 41 the same task revealed a significant (but not complete) reduction in the number of contralesional omissions. Ipsilesional targets were, in contrast, still errorless detected. The coupling of a bottom-up (target change) and a top-down (dual-tasking) manipulation revealed the presence of a long-lasting spontaneous recovery from contralesional spatial awareness deficits. In contrast, neither manipulation was effective when implemented separately. After having excluded the potential confound of practice effects, it was concluded that not only the presence but also the time course of hemispatial neglect strongly depends on the degree of attentional engagement required by the task.

Neglect and extinction depend greatly on task demands: a review

This review illustrates how, after unilateral brain damage, the presence and severity of spatial awareness deficits for the contralesional hemispace depend greatly on the quantity of attentional resources available for performance. After a brief description of neglect and extinction, different frameworks accounting for spatial and non-spatial attentional processes will be outlined. The central part of the review describes how the performance of brain-damaged patients is negatively affected by increased task demands, which can result in the emergence of severe awareness deficits for contralesional space even in patients who perform normally on paper-and-pencil tests. Throughout the review neglect is described as a spatial syndrome that can be exacerbated in the presence and severity by both spatial and non-spatial tasks. The take-home message is that the presence and degree of contralesional neglect and extinction can be dramatically overlooked based on standard clinical (paper-and-pencil) testing, where patients can easily compensate for their deficits. Only tasks where compensation is made impossible represent an appropriate approach to detect these disabling contralesional deficits of awareness when they become subtle in post-acute stroke phases.

Increased attentional demands impair contralesional space awareness following stroke

Rate and severity of contralesional loss of awareness following stroke is highly variable across patients and assessment methods. We studied whether the degree of impairment for contralesional space awareness depends on the quantity of attentional resources that are available for task performance. A new computer-based paradigm was used to assess visual extinction and single-target detection rate in four right hemisphere stroke patients. In the single-task condition, they had to report only the position of the target(s) ("right", "left", or "both" sides). In the dual-task conditions, patients also performed a second task, visual or auditory, that recruited additional attentional resources. The same tasks were also performed by healthy controls and by a left hemisphere stroke patient. Patients' performance was apparently unimpaired in the single-task condition. In contrast, dramatic failures to report the left-sided target emerged in the dual-task conditions. The performance of control participants was unaffected by the dual-task manipulation, whereas the left stroke patient showed the opposite pattern (i.e., unawareness of right-sided targets). Severe contralesional space unawareness under dual-task conditions reveals that visuospatial deficits can dramatically emerge when attentional resources are consumed by a concurrent task. Apparently spared contralesional awareness may simply reflect the availability of resources that are just sufficient to perform a single-task. This finding has important implications for the assessment of contralesional space awareness following stroke, because everyday life activities are often more demanding than most of the tests adopted for diagnosing space awareness disorders.