Horizontal Line Bisection Research Articles

Altered Allocation of Vertical Attention in Individuals With Autism Spectrum Disorder.

Typical adults most frequently orient their attention to other people's eyes, whereas individuals with autism spectrum disorder (ASD) orient their attention to other people's mouths. Typical adults also reveal visuospatial biases on tasks such as vertical and horizontal line bisections. Therefore, the difference in face viewing might be related to a more general group difference in the allocation of vertical attention. To use vertical line bisection and quadrisection tasks to evaluate whether individuals with ASD have a more downward-oriented vertical attentional bias than do typical individuals. We recruited 20 individuals with ASD and 20 control participants matched for age (6-23 years), IQ, and sex. We asked the individuals to bisect and quadrisect lines on the top and bottom when the vertical lines were placed at the intersection of their right, left, and center egocentric sagittal planes and their coronal plane. The distances from the true midpoint and quadripoint were measured, and between-group performances were compared. No significant difference was found between the ASD and control groups for vertical line bisections or lower line quadrisections. However, when the ASD group was compared with the control group for higher line quadrisections, the ASD group exhibited a greater upward deviation. There is no downward vertical attentional spatial bias associated with ASD that could help to explain these individuals' attentional bias toward the mouth. However, additional studies are required to learn if this atypical upward vertical attentional bias might account for some of the symptoms and signs associated with ASD.

Leftward Spatial Bias in Dialyzed Patients With End-Stage Renal Disease: A Sign of Right Hemispheric Attentional Activation or Impaired Left-Sided Disengagement?

In the horizontal line bisection task, patients with end-stage renal disease (ESRD) treated with dialysis typically have an increase in the normal leftward attentional bias. It is not clear, however, whether this increased bias is related to an increase of attention toward left hemispace or impaired disengagement from left-sided stimuli. Non-demented patients with ESRD who were being treated with dialysis and demographically matched healthy controls attempted to bisect series of horizontal lines composed of two segments of unequal length and width, with the longer segment placed to the right or left. To test for the presence of a global spatial attentional bias, participants attempted to find the middle of the whole line. To test for focal attentional engagement and attentional disengagement, participants were asked to bisect only the longer segment of these compound lines. For the global condition, both patients and healthy controls were biased toward the longer segment and more so to the left. In the focal condition, when the longer segment was on the right side, both groups deviated their bisections toward the shorter segment. However, when in the focal condition the longer segment was on the left healthy controls deviated their bisection significantly more rightwards than did the patients, whereas with the longer segment on the right, the patients and healthy controls did not differ in their bias. These results suggest that the previously recognized dysfunction of the right fronto-subcortical attentional network in dialyzed patients might account for the results of the current study.

Disruptions of the Human Connectome Associated With Hemispatial Neglect.

Background and ObjectivesHemispatial neglect is a heterogeneous and complex disorder that can be classified by frame of reference for “left” vs “right,” including viewer-centered neglect (VCN, affecting the contralesional side of the view), stimulus-centered neglect (SCN, affecting the contralesional side of the stimulus, irrespective of its location with respect to the viewer), or both. We investigated the effect of acute stroke lesions on the connectivity of neural networks that underlie VCN or SCN.MethodsA total of 174 patients within 48 hours of acute right hemispheric infarct underwent a detailed hemispatial neglect assessment that included oral reading, scene copy, line cancellation, gap detection, horizontal line bisection tests, and MRI. Each patient's connectivity map was generated. We performed a linear association analysis between network connectivity strength and continuous measures of neglect to identify lesion-induced disconnections associated with the presence or severity of VCN and SCN. Results were corrected for multiple comparisons.ResultsAbout 42% of the participants with right hemisphere stroke had at least one type of neglect. The presence of any type of neglect was associated with lesions to tracts connecting the right inferior parietal cortex, orbitofrontal cortex, and right thalamus to other right-hemispheric structures. VCN only was strongly associated with tracts connecting the right putamen to other brain regions and tracts connecting right frontal regions with other brain regions. The presence of both types of neglect was most strongly associated with tracts connecting the right inferior and superior parietal cortex to other brain regions and those connecting left or right mesial temporal cortex to other brain regions.DiscussionOur study provides new evidence for the specific white matter tracts where disruption can cause hemispatial neglect in a relatively large number of participants and homogeneous time after onset. We obtained MRI and behavioral testing acutely, before the opportunity for rehabilitation or substantial recovery.Classification of EvidenceThis study provides Class II evidence that damage to specific white matter tracts identified on MRI are associated with the presence of neglect following right hemispheric stroke.

Age-related changes in the allocation of spatially directed focal attention

ABSTRACT Objectives Leftward deviation on a horizontal line bisection test (pseudoneglect) might be induced by right hemispheric dominance for mediating spatial or global attention, or a hemispheric asymmetry in the ability to spatially disengage attention. With aging, this leftward bias is reduced, likely due to the aging-related deterioration of right hemisphere mediated functions (right hemi-aging) or hemispheric asymmetry reduction in old adults (HAROLD). Methods Forty-seven healthy adults divided into younger and older groups performed a modified Posner spatial-attentional task. Results Overall, younger individuals responded faster to left than right-sided imperative stimuli. In contrast, older participants did not reveal a right-left asymmetry to imperative stimuli. The younger group also revealed a strong inverse relationship between the reaction time to right valid cues and the leftward attentional bias while performing the line bisection task (pseudoneglect). Conclusions Our results provide support for both the right hemisphere spatial-attentional dominance hypothesis of pseudoneglect and the right hemi-aging hypotheses.

Modulation of human visuospatial attention analysis by transcranial direct current stimulation (tDCS) in the line bisection performance.

The general population shows physiologic biases in the line bisection performance for visuospatial attention, almost to the left known as pseudoneglect. Previous studies have shown that tDCS affects visuospatial attention in line bisection. This research applies tDCS over left posterior parietal cortice (P3) or right posterior parietal cortice (P4) to explore the effect on pseudoneglect. Subjects randomly were divided into five groups by stimulation distribution: (i) P3-anodal (P3A), (ii) P3-cathodal (P3C), (iii) P4-anodal (P4A), (iv) P4-cathodal (P4C), (v) sham. Participants respectively finished the post-tDCS line-bisection assignment (lines on the left/right side of the monitor (LL/LR), and lines in the center of the monitor (LC)) the same as the pre-tDCS task over the session (P3A, P3C, P4A, P4C and sham) tDCS condition. The principal findings were that P3A tDCS reduced the leftward shift in the horizontal line bisection task, as well as P4C tDCS reduced the leftward shift in LL. Sham stimulation as well as P3C and P4A stimulation didn’t have systematic improvements in the line bisection tasks. Therefore, an activation–orientation model of pseudoneglect is corroborated by these findings. Activation of intact structures in the rebalance of left and right parietal cortex might impose modulating effects on tDCS.

The Influence of Focused and Sustained Spatial Attention on the Allocation of Spatial Attention.

The objective of this study was to evaluate the impact of directed and sustained attention on the allocation of visuospatial attention. Healthy people often have left lateral and upward vertical spatial attentional biases. However, it is not known whether there will be an increase in bias toward the attended portion of the stimulus when volitional spatial attention is allocated to a portion of a stimulus, whether there are asymmetrical spatial alterations of these biases, and how sustained attention influences these biases. We assessed spatial bias in 36 healthy, right-handed participants using a variant of horizontal and vertical line bisections. Participants were asked to focus on one or the other end of vertical or horizontal lines or entire vertical or horizontal lines, and then to bisect the line either immediately or after a 20 second delay. We found a significant main effect of attentional focus and an interaction between attentional focus and prolonged viewing with delayed bisection. Focusing on a certain portion of the line resulting in a significant deviation toward the attended portion and prolonged viewing of the line prior to bisection significantly enhanced the degree of deviation toward the attended portion. The enhanced bias with directed and sustained attention may be useful modifications of the line bisection test, particularly in clinical populations. Thus, future studies should determine whether prolonged viewing with delayed bisection and spatially focused attention reveals attentional biases in patients with hemispheric lesions who perform normally on the traditional line bisection test. (JINS, 2019, 25, 65-71).

Chapter 14 - Unilateral spatial neglect after posterior parietal damage

Unilateral spatial neglect is a disabling neurologic deficit, most frequent and severe after right-hemispheric lesions. In most patients neglect involves the left side of space, contralateral to a right-hemispheric lesion. About 50% of stroke patients exhibit neglect in the acute phase. Patients fail to orient, respond to, and report sensory events occurring in the contralateral sides of space and of the body, to explore these portions of space through movements by action effectors (eye, limbs), and to move the contralateral limbs. Neglect is a multicomponent higher-level disorder of spatial awareness, cognition, and attention. Spatial neglect may occur independently of elementary sensory and motor neurologic deficits, but it can mimic and make them more severe. Diagnostic tests include: motor exploratory target cancellation; setting the midpoint of a horizontal line (bisection), that requires the estimation of lateral extent; drawing by copy and from memory; reading, assessing neglect dyslexia; and exploring the side of the body contralateral to the lesion. Activities of daily living scales are also used. Patients are typically not aware of neglect, although they may exhibit varying degrees of awareness toward different components of the deficit. The neural correlates include lesions to the inferior parietal lobule of the posterior parietal cortex, which was long considered the unique neuropathologic correlate of neglect, to the premotor and to the dorsolateral prefrontal cortices, to the posterior superior temporal gyrus, at the temporoparietal junction, to subcortical gray nuclei (thalamus, basal ganglia), and to parietofrontal white-matter fiber tracts, such as the superior longitudinal fascicle. Damage to the inferior parietal lobule of the posterior parietal cortex is specifically associated with the mainly egocentric, perceptual, and exploratory extrapersonal, and with the personal, bodily components of neglect. Productive manifestations, such as perseveration, are not a correlate of posterior parietal cortex damage.

Dissociation between line bisection and mental-number-line bisection in healthy adults

Healthy adults bisect visual horizontal lines slightly to the left of their true center. This bias has been termed “pseudoneglect” and is considered to reflect right hemisphere dominance in the orienting of spatial attention. A previous investigation reported a positive correlation between pseudoneglect and a corresponding negative bias towards numbers lower than the true midpoint, i.e. supposedly to the left of the midpoint, during the mental bisection of number intervals that were defined by two visual arabic digits presented one to the left and one to the right of a horizontal line (Longo and Lourenco, 2007, Neuropsychologia, 45, 7, 1400–1407). Here, studying a sample of 60 healthy participants we verified whether this correlation still holds when the endpoints of number intervals are defined verbally, i.e. with no visual-spatial cues suggesting their left-to-right arrangement. Participants bisected horizontal lines (2cm, 10cm and 20cm), short number intervals (3-, 5-, 7- and 9-unit) and large number intervals (16-, 24-, 32-, 40-, 48-, 56-, and 64-unit). Pseudoneglect was observed both in line and number interval bisection, confirming the results of Longo and Lourenco (2007). Nonetheless, the study of correlations between bisection biases averaged across different line and number intervals lengths and between all possible pairings of line and number interval lengths revealed no significant or systematic pattern. During line bisection pseudoneglect increased as a function of line length while with short number intervals pseudoneglect decreased and turned into an opposite positive bias as a function of interval length. With large number intervals no linear relationship was present between bisection bias and interval length and, as in Longo and Lourenco (2007), the higher was the starting point of the number interval the larger was pseudoneglect. These results show that verbally defined number intervals are not mentally inspected with the same mechanisms that are engaged by the bisection of horizontal visual lines. This suggests that number intervals are not inherently arranged along the mental equivalent of a left-to-right oriented horizontal line. This spatial representation seems rather adopted when, as in the case of the SNARC task, “left” vs. “right” codes must be used for the selection of responses associated with numbers or when, as in the case of Longo and Lourenco (2007), the numerical material to be processed is arranged in left-to-right order.

The Effects of Chronic Right Hemispheric Damage on the Allocation of Spatial Attention: Alterations of Accuracy and Reliability.

Right hemispheric damage (RHD) caused by strokes often induce attentional disorders such as hemispatial neglect. Most patients with neglect over time have a reduction in their ipsilesional spatial attentional bias. Despite this improvement in spatial bias, many patients remain disabled. The cause of this chronic disability is not fully known, but even in the absence of a directional spatial attentional bias, patients with RHD may have an impaired ability to accurately and precisely allocate their spatial attention. This inaccuracy and variable directional allocation of spatial attention may be revealed by repeated performance on a spatial attentional task, such as line bisection (LBT). Participants with strokes of their right versus left (LHD) hemisphere along with healthy controls (HC) performed 24 consecutive trials of 24 cm horizontal line bisections. A vector analysis of the magnitude and direction of deviations from midline, as well as their standard deviations (SD), were calculated. The results demonstrated no significant difference between the LHD, RHD and HC groups in overall spatial bias (mean bisection including magnitude and direction); however, the RHD group had a significantly larger variability of their spatial errors (SD), and made larger errors (from midline) than did the LHD and HC groups. There was a curvilinear relationship between the RHD participants' performance variability and their severity of their inaccuracy. Therefore, when compared to HC and LHD, the RHD subjects' performance on the LBT is more variable and inaccurate.

Line bisection in Parkinson's disease: Investigation of contributions of visual field, retinal vision, and scanning patterns to visuospatial function.

Parkinson's disease (PD) is characterized by disorders of visuospatial function that can impact everyday functioning. Visuospatial difficulties are more prominent in those whose motor symptoms begin on the left body side (LPD) than the right body side (RPD) and have mainly been attributed to parietal dysfunction. The source of visuospatial dysfunction is unclear, as in addition to subcortical-cortical changes, there are irregularities of visual scanning and potentially of retinal-level vision in PD. To assess these potential contributors, performance on a visuospatial task--line bisection--was examined together with retinal structure (nerve fiber layer thickness, measured by optical coherence tomography [OCT]), retinal function (contrast sensitivity, measured by frequency-doubling technology [FDT]), and visual scanning patterns. Participants included 20 nondemented patients (10 LPD, 10 RPD) and 11 normal control (NC) adults. Relative to the other groups, LPD were expected to show rightward bias on horizontal line bisection, especially within the left visual hemispace, and downward bias on vertical bisection. LPD relative rightward bias was confirmed, though not mainly within the left hemispace and not correlated with retinal structure or function. Retinal thinning was seen in LPD relative to RPD. Qualitative visualization of eye movements suggested greater LPD exploration of the right than left side of the line during horizontal bisection, and some overall compression of scanning range in RPD (both orientations) and LPD (primarily vertical). Results indicated that rightward visuospatial bias in our LPD sample arose not from abnormalities at the retinal level but potentially from attentional biases, reflected in eye movement patterns.

Line bisection error predicts the presence and severity of neglect dyslexia in paragraph reading

Cancellation tasks and line bisection tasks are commonly used to diagnose spatial neglect after right hemisphere lesions. In such tasks, neglect patients often show leftsided omissions of targets in cancellation tests as well as a pathological rightward deviation in horizontal line bisection. However, double dissociations have also been reported and the relation between performance in both tasks is not clear. Another impairment frequently associated with the neglect syndrome are omissions or misread initial letters of single words, a phenomenon termed neglect dyslexia (ND). Omissions of whole words on the contralesional side of the page are generally considered as egocentric or space-based errors, whereas misreadings of the left part of a word in ND can be viewed as a type of stimulus-centered or word-based, perceptual error. As words, sentences and horizontal lines have a similar spatial layout in the sense that they all are horizontally aligned, long stimuli with a canonical left–right orientation (with a defined beginning on the left and an end on the right side), we hypothesized a significant association between the horizontal line bisection error (LBE) in neglect and the extent (number) of neglected or substituted letters within single words in ND (neglect dyslexia extension, NDE). To this purpose, we computed Center-of-Cancellation (CoC) scores in a cancellation task as well as Center-of-Reading (CoR) scores in an experimental paragraph reading test. We found that the CoR was a better indicator for egocentric word omissions than the CoC in a group of 17 patients with left visuospatial neglect. Furthermore, the LBE predicted the severity of ND, indicated by highly significant correlations between the LBE and the extent of the neglected letter string within single words (NDE; r=0.73, p<0.001) as well as between the LBE and the frequency of ND errors (r=0.61; p=0.009). In contrast, we found no significant correlation between the CoC and the severity of ND. These results indicate two different pathological mechanisms being responsible for contralesional spatial neglect and ND. In conclusion, the LBE is a more sensitive predictor of the presence and severity of the reading disorder in spatial neglect than conventional cancellation tasks.

The neural correlates of impaired collision avoidance in hemianopic patients

The aim of this study was to assess the brain regions associated with impaired performance in a virtual, dynamic collision avoidance task, in a group of patients with homonymous visual field defects (HVFDs) because of unilateral vascular brain lesions. Overall task performance was quantitatively assessed as the number of collisions while crossing an intersection at two levels of traffic density. Twenty-six patients were divided into two subgroups using the median split method: patients with 'performance above average' (HVFD(A), i.e. lower number of collisions) and patients with 'performance below average' (HVFD(B), i.e. higher number of collisions). In order to identify the anatomical structures that might be specifically affected in HVFD(B) patients but spared in HVFD(A) patients, overlap, subtraction and voxel-based lesion-symptom mapping analyses were performed using the MRIcron software. No significant difference in collision avoidance between patients with left- and right-hemispheric lesions was revealed. Separate lesion analysis in 12 patients with right- and 14 patients with left-hemispheric lesions showed that the cortical structures associated with impaired collision avoidance were the parieto-occipital region and posterior cingulate gyrus in the right hemisphere and the inferior occipital cortex and parts of the fusiform (occipito-temporal) gyrus in the left hemisphere. In the present collision avoidance paradigm, impaired performance of patients with right-hemispheric lesions is associated with damage in the dorsal processing stream and potential impact on the visual spatial working memory (WM), while impaired performance of patients with left-hemispheric lesions is associated with damage in the ventral stream and potential impact on the visual object WM.

Bisection and dissection of horizontal lines: The long and the short of the Oppel-Kundt illusion

Bisection and dissection of horizontal lines: The long and the short of the Oppel-Kundt illusion

Bisection and dissection of horizontal lines: The long and the short of the Oppel-Kundt illusion

Bisection and dissection of horizontal lines: The long and the short of the Oppel-Kundt illusion

Galvanic vestibular stimulation reduces the pathological rightward line bisection error in neglect—A sham stimulation-controlled study

Patients with right hemisphere lesions often show left spatial neglect and the typical rightward deviation in horizontal line bisection. Previous studies have shown that sensory stimulation modulates line bisection. A less well-known but promising sensory stimulation method is galvanic vestibular stimulation (GVS). This non-invasive technique leads to activation of the vestibular cortices and adjacent cortical areas in the temporo-parietal cortex via polarization effects of the vestibular nerves. This is accomplished by application of weak direct currents, delivered by two electrodes attached to the mastoids. Despite the relative benefits of GVS its effects on line bisection have not yet been studied in neglect patients. Thus, the present study investigated the impact of GVS on performance in a modified line bisection task in right-brain damaged patients with versus without leftsided visual neglect. In neglect patients, but not in control patients, left-cathodal and right-cathodal GVS significantly reduced the rightward line bisection error as compared to Baseline (without GVS) and sham stimulation. A larger decrease of the rightward line bisection error was observed during right-cathodal GVS. Sham stimulation showed no specific effects on line bisection. The beneficial effects of GVS might be due to activation of preserved structures of the lesioned right posterior parietal cortex which is known to be involved in line bisection.

Attention biases the perceived midpoint of horizontal lines

In patients with right brain damage and left visual neglect, attention tends to be captured by right-sided objects and cannot easily disengage from them. While these phenomena can account for several clinical and experimental patterns of performance such as biased visual search, its role is more controversial for other neglect-related signs, such as the typical rightward shifts in horizontal line bisection. It is thus important to see whether and how attentional orienting can bias line bisection in normal participants using standard clinical bisection stimuli. In 3 experiments, we explored the Attentional Repulsion Effect (ARE, Suzuki & Cavanagh, 1997) on pre-bisected lines. Normal observers saw horizontal lines with a vertical bisection mark near the center, preceded by a cue to the left or right of the line, or by no cue. On each trial, observers indicated whether they saw the bisection mark to the left or at the right of the midpoint. We plotted the proportion of ‘seen-at-right’ responses as a function of the mark's actual position. For uncued lines, the point of subjective equality was slightly at the left of the true center, consistent with the pseudoneglect phenomenon. Right-sided cues shifted the apparent bisection point to the left (and vice versa), as predicted by the ARE. Similar results occurred with different task instructions (compare the length of the left-sided line segment to the right-sided segment) and in the presence or absence of central fixation marks. These results obtained in normal participants support attentional accounts of biased line bisection in neglect patients.

Neglect Is More Common and Severe at Extreme Hemoglobin Levels in Right Hemispheric Stroke

Anemia is 1 potential mechanism by which the brain receives inadequate oxygenation. The purpose of this study was to determine in acute stroke patients whether lower hemoglobin values were associated with worse hemispatial neglect. In 203 subjects, neglect testing batteries were administered within 24 hours of admission for acute right hemispheric stroke. We analyzed the error rate on each test as well as "any neglect" (z score >or=2 on any of 3 selected tests compared with normal controls), as predicted by hemoglobin level, with adjustment for infarct size, National Institutes of Health Stroke Scale score, age, and sex. The association between hemoglobin and neglect varied on the basis of hemoglobin level. At lower hemoglobin levels (<12 g/dL), each 1-point higher hemoglobin value was protective (adjusted odds ratio=0.56; 95% CI, 0.35 to 0.89) from having "any neglect." However, for a hemoglobin value >14 g/dL, each 1-point higher hemoglobin value was associated with higher odds of having neglect (adjusted odds ratio=1.67; 95% CI, 1.09 to 2.57). Similar relations were found for predicted error rate on the horizontal line bisection, line cancellation, and copy Ogden scene neglect tests. These relations seemed to be more pronounced in individuals who had a diffusion/perfusion mismatch. Lower and higher hemoglobin levels were each associated with increased odds of neglect and with worse severity of neglect, independent of stroke size and severity. Higher hemoglobin values may represent dehydration or hyperviscosity. The importance of the extremes of hemoglobin in identifying individuals at risk for worse functional consequences of stroke warrants further study.

Oblique spatial shifts of subjective visual straight ahead orientation in quadrantic visual field defects

Patients with postchiasmatic visual field defects often show a contralesional bias towards the scotoma in line bisection or when indicating their visual subjective straight ahead (VSSA). Recent evidence suggests a retinotopic misrepresentation of visual space in patients with homonymous quadrantanopia (HQ). We therefore assessed in the present study whether patients with HQ show an oblique shift of their VSSA towards their scotoma, in addition to the known bias in horizontal line bisection. Moreover, we examined whether eccentric fixation contributes to this shift. To this purpose, 15 non-neglecting stroke patients with HQ and 15 matched healthy control subjects were assessed in horizontal line bisection and in the horizontal and vertical dimension of their VSSA. Additionally, perimetric blind spot mapping was performed. Eight out of nine patients with left quadranopia showed the typical leftsided, horizontal line bisection error, while only one out of seven patients with rightsided quadranopia showed a rightsided shift. Normal subjects showed a non-significant leftward shift in line bisection (pseudoneglect). All 15 patients with HQ showed a large oblique shift of their VSSA towards the blind quadrants, while normal subjects showed no systematic left-rightward shift, but a small downward shift of the VSSA. The position of the blind spot was normal in all testable eyes of patients and control subjects, thus excluding eccentric fixation or cyclorotation of the eyes. In conclusion, our study reveals a hitherto unreported oblique spatial shift of subjective visual body orientation towards the blind quadrants in non-neglecting patients with quadranopia.

Line bisection in unilateral homonymous visual field defects

The contralesional line bisection error in unilateral homonymous hemianopia is a frequent but neglected clinical phenomenon. Our knowledge about this bisection error is based on small samples of hemianopic patients. Moreover, horizontal line bisection has never been investigated in other unilateral visual field defects. The present study is the first to examine line bisection in a large, representative sample of patients with unilateral homonymous visual field defects. We investigated horizontal line bisection in 129 patients with left- or right-sided homonymous hemianopia (60.5%), upper and lower quadranopia (24.8%), and paracentral scotoma (14.7%), and determined the magnitude and direction of line bisection error. The contralesional horizontal line bisection error was present not only in patients with hemianopia but also in those with upper or lower quadranopia or paracentral scotoma. Neither the type nor the severity of the visual field defect was found to determine the bisection error. Only the side of the field defect seemed to determine the horizontal direction of the bisection error (left-/rightward). The contralesional bisection error is not a specifically “hemianopic” phenomenon. It is frequently associated with any unilateral homonymous visual field defect, i.e., hemianopia, upper/lower quadranopia, paracentral scotoma. Moreover, our results further support the recent finding that the contralesional bisection error is not a direct consequence of the visual field defect. Yet, they also suggest that, although the visual field defect does not seem to be the primary cause of the contralesional bisection error, it may nevertheless contribute to it.

Normalization of horizontal pseudoneglect following right, but not left, upper limb amputation

ObjectivesSubjects who have suffered limb amputations are known to have physiological alterations of their body's representation, or schema. Such changes of brain function might alter the right–left spatial allocation of attention. The goal of this study was to learn if, compared to normal subjects, limb amputees had alterations of right–left spatial attention. MethodsThe subjects were veterans with amputation of one upper or lower limb. All subjects performed horizontal line bisections in their left, middle and right body-centered space. ResultsFollowing right upper limb amputation, there appears to be a reduction of the normal left-sided bias (pseudoneglect) primarily for lines presented in the right body hemispace. ConclusionsThis amputation-induced alteration of attentional bias might be related to changes in the body schema, a compensatory strategy, or alterations of scanning patterns. Further studies are needed to reproduce these results and to learn the underlying brain mechanism.