Weights and measures: A new look at bisection behaviour in neglect

A scoping review and critique of the Input-Output subtyping dimension of spatial neglect

Spatial neglect is a common and debilitating disorder after stroke whereby individuals have difficulty reporting, orienting, and/or responding to the contralesional side of space. Given the heterogeneity of neglect symptom presentation, various neglect subtypes have been proposed to better characterize the disorder. This review focuses on the distinction between Input neglect (i.e., difficulty perceiving and/or attending to contralesional stimuli) and Output neglect (i.e., difficulty planning and/or executing movements toward contralesional stimuli). Conceptualizations of Input and Output neglect have varied considerably. We provide a novel summary of the terminology, measurement approaches, and neural correlates of these subtypes. A protocol detailing our systematic scoping review strategy is registered on the Open Science Framework (https://osf.io/bvtxf/). For feasibility and greater comparability across studies, we limited our inclusion criteria to tasks focused on visual stimuli and upper-limb movements. A total of 110 articles were included in the review. Subtyping tasks were categorized based on whether they mainly manipulated aspects of the input (i.e., congruence of visual input with motor output, presence of visual input) or the output (i.e., modality, goal, or direction of output) to produce an Input-Output subtype dissociation. We used our review results to identify four main critiques of this literature: 1) lack of consistency/clarity in conceptual models; 2) methodological issues of dissociating Input and Output subtypes; 3) a need for updated neural theories; and 4) barriers to clinical application. We discuss the lessons learned from this subtyping dimension that can be applied to future research on neglect subtype assessment and treatment.

Beyond bias: A registered examination of the validity of using line bisection to measure non-lateralised attention

Line bisection is a task widely used to assess lateral asymmetries of attention, in which participants are asked to mark the midpoint of a horizontal line. The directional bisection error (DBE) from the objective midpoint of the line is the traditional measure of performance. However, an alternative method of studying the bisection behaviour, the endpoint weightings method, has been proposed. This method produces two measures of performance: endpoint weightings bias (EWB) and endpoint weightings sum (EWS). While EWB measures attentional asymmetry, it has been suggested that EWS quantifies the total (non-lateralised) attention allocated to the task. If EWS provides a valid index of non-lateralised attention, then changes in tonic and phasic arousal should systematically affect EWS. In this article, we formally tested this prediction, using time on task to manipulate tonic arousal and unpredictable auditory tones, presented simultaneously with line stimuli, to manipulate phasic arousal. Our registered analyses revealed that neither of our manipulations for tonic or phasic arousal significantly influenced EWS. Therefore, the null hypotheses cannot be rejected. An exploratory analysis of all trials and conditions revealed a significant reduction in EWS with time spent on task. However, the lack of any significant effect of the alerting tone on EWS suggests that EWS may not be a valid measure of generalised attention to the task.

The line bisection bias as a deficit of proportional reasoning - evidence from number line estimation in neglect

This study aimed to investigate whether neurological patients presenting with a bias in line bisection show specific problems in bisecting a line into two equal parts or their line bisection bias rather reflects a special case of a deficit in proportional reasoning more generally. In the latter case, the bias should also be observed for segmentations into thirds or quarters. To address this question, six neglect patients with a line bisection bias were administered additional tasks involving horizontal lines (e.g., segmentation into thirds and quarters, number line estimation, etc.). Their performance was compared to five neglect patients without a line bisection bias, 10 patients with right hemispheric lesions without neglect, and 32 healthy controls. Most interestingly, results indicated that neglect patients with a line bisection bias also overestimated segments on the left of the line (e.g., one third, one quarter) when dissecting lines into parts smaller than halves. In contrast, such segmentation biases were more nuanced when the required line segmentation was framed as a number line estimation task with either fractions or whole numbers. Taken together, this suggests a generalization of line bisection bias towards a segmentation or proportional processing bias, which is congruent with attentional weighting accounts of line bisection/neglect. As such, patients with a line bisection bias do not seem to have specific problems bisecting a line, but seem to suffer from a more general deficit processing proportions.

Reducing alertness does not affect line bisection bias in neurotypical participants

Alertness, or one's general readiness to respond to stimulation, has previously been shown to affect spatial attention. However, most of this previous research focused on speeded, laboratory-based reaction tasks, as opposed to the classical line bisection task typically used to diagnose deficits of spatial attention in clinical settings. McIntosh et al. (Cogn Brain Res 25:833-850, 2005) provide a form of line bisection task which they argue can more sensitively assess spatial attention. Ninety-eight participants were presented with this line bisection task, once with and once without spatial cues, and both before and after a 50-min vigilance task that aimed to decrease alertness. A single participant was excluded due to potentially inconsistent behaviour in the task, leaving 97 participants for the full analyses. While participants were, on a group level, less alert after the 50-min vigilance task, they showed none of the hypothesised effects of reduced alertness on spatial attention in the line bisection task, regardless of with or without spatial cues. Yet, they did show the proposed effect of decreased alertness leading to a lower level of general attention. This suggests that alertness has no effect on spatial attention, as measured by a line bisection task, in neurotypical participants. We thus conclude that, in neurotypical participants, the effect of alertness on spatial attention can be examined more sensitively with tasks requiring a speeded response compared to unspeeded tasks.

Spatial Neglect Therapy With the Augmented Reality App "Negami" for Active Exploration Training: A Randomized Controlled Trial on 20 Stroke Patients With Spatial Neglect

OBJECTIVE

To investigate the efficacy of the augmented reality (AR) app "Negami" as an active exploration training for the treatment of spatial neglect. Improvements of the ipsilesional attention and orientation bias (and resulting contralesional neglect) will be examined in stroke patients with spatial neglect and compared with a control group.

DESIGN

Randomized controlled trial with an experimental Negami group, consisting of patients with spatial neglect, and a group of neglect patients receiving standard neglect therapy.

SETTING

Three rehabilitation hospitals.

PARTICIPANTS

Twenty right hemispheric stroke patients with spatial neglect (N=20).

INTERVENTION

Over a period of 2 weeks, both groups received 5 training sessions per week (à 25 minutes). Neglect behavior was assessed weekly over a 5-week period, with the Negami therapy group receiving a second follow-up assessment at 1-to-2-month intervals after completion of training.

MAIN OUTCOME MEASURES

Letter Cancellation, Bells Test, Copying Task, Line Bisection Task, and a self-developed "Exploration Test".

RESULTS

Both groups improved significantly. While the Negami therapy group improved in 4 of 5 neglect tests used, the standard therapy group improved in only 1 of these tests. We observed significantly better improvement in the Negami group already after the first week of training. This difference was also significant after the end of the training as well as 1 week after the end of training and remained stable 1-2 months after the end of treatment.

CONCLUSION

Negami can be used as an effective alternative or addition to current standard neglect therapy, and may even be superior to it.

Full-field input generated from right visual field information for healthy participants reproduces performance simulating left unilateral spatial neglect in line bisection

Patients with left unilateral spatial neglect (USN) typically place the subjective midpoint to the right of the objective centre when bisecting a horizontal line. This pathological phenomenon may be explained as a result of greater dependence on the right endpoint in the external reference frame (Koyama et al., Brain Cogn, 35, 1997, 271; McIntosh et al., Cogn Brain Res, 25, 2005, 833). Ishiai et al. (Brain, 112, 1989, 1485) reported that once patients with USN fixated on a certain point on the right part of the presented line, they persisted with this point and marked the subjective midpoint there without leftward searches. Ishiai et al.'s interpretation was that the patients saw a totalised line representation that extended equidistantly to the right and left sides, based on the information of the attended rightward extent from the subjective midpoint. Accordingly, we used virtual reality goggles (VRG) and devised a mirror-image viewing (MV) condition that showed a full-field view based on the right visual field information to test whether healthy participants would thereby show neglect-like bisection performance. The participants were 30 healthy adults (22-37 years old; 15 women and 15 men). In this condition, 96.7% (29/30) of participants were judged to exhibit USN-like performance of line bisection, indicating the effectiveness of MV condition to simulate USN. The novelty of the present study lies in the use of a task-specific intervention of neglect-like visuospatial processing during line bisection without attempting to modify the direction of spatial attention. This approach may contribute to the understanding of the pathological visuospatial processing of USN.

Neglecting the bottom space: an object-based disorder? A two-case observational study

Altitudinal neglect is an atypical form of spatial neglect where brain-damaged patients neglect the lower, or sometimes the upper, part of the space. Our understanding of this phenomena is limited, with unknown occurrence across different reference frames, such as distance (peripersonal vs. extrapersonal) and system of reference (egocentric vs. allocentric). Two patients with acute bilateral (P1) or right hemispheric (P2) stroke, with signs of bottom altitudinal neglect, underwent an extensive evaluation of neglect within 10 days post-stroke. Assessments involved altitudinal neglect and unilateral spatial neglect (USN) in peripersonal space, exploring egocentric and allocentric signs and in extrapersonal space. Compared to a control group of 15 healthy age-matched subjects, patients showed allocentric and egocentric left USN in peripersonal space, and mostly allocentric signs of altitudinal neglect. No signs of neglect were evidenced in extrapersonal space. Altitudinal neglect could thus present as an allocentric form of spatial neglect, suggesting that allocentric representations may not only affect the deployment of attentional resources along horizontal dimensions but also operate along vertical dimensions. Future studies should deepen our understanding of altitudinal neglect, eventually leading to further unravel spatial processes that control attention, their corresponding brain mechanisms, and implications for patients' rehabilitation and functional outcome.

[Clinical examination of spatial neglect and other disorders of spatial cognition]

Neglect occurring after stroke, neoplasms or degenerative processes can lead to considerable disability in everyday life as can other disorders of spatial orientation. Therefore, a dedicated examination and early diagnostic classification are obligatory. Behavioral tests are helpful in this respect, enabling the clinician to obtain an initial overview of the existing deficits even at the patient's bedside. The clinical (bedside) examination of spatial neglect as well as the corresponding differential diagnostic procedure for the clarification of (possibly additionally or exclusively existing) hemianopia and extinction, as well as the examination of disorders of visuospatial perception, visuoconstructive disorders, topographic disorders, Bálint's syndrome, simultanagnosia, and optic ataxia are presented. The presentation is based on the newly revised (year 2023) guidelines of the Association of the Scientific Medical Societies in Germany (AWMF) on this subject area.

Negami: An Augmented Reality App for the Treatment of Spatial Neglect After Stroke

BACKGROUND

A widely applied and effective rehabilitation method for patients experiencing spatial neglect after a stroke is "visual exploration training." Patients improve their ipsilesional bias of attention and orientation by training exploration movements and search strategies toward the contralesional side of space. In this context, gamification can have a positive influence on motivation for treatment and thus on the success of treatment. In contrast to virtual reality applications, treatment enhancements through augmented reality (AR) have not yet been investigated, although they offer some advantages over virtual reality.

OBJECTIVE

This study aimed to develop an AR-based app (Negami) for the treatment of spatial neglect that combines visual exploration training with active, contralesionally oriented rotation of the eyes, head, and trunk.

METHODS

The app inserts a virtual element (origami bird) into the real space surrounding the patient, which the patient explores with the camera of a tablet. Subjective reports from healthy elderly participants (n=10) and patients with spatial neglect after stroke (n=10) who trained with the new Negami app were analyzed. Usability, side effects, and game experience were assessed by various questionnaires.

RESULTS

Training at the highest defined difficulty level was perceived as differently challenging but not as frustrating by the group of healthy elderly participants. The app was rated with high usability, hardly any side effects, high motivation, and entertainment. The group of patients with spatial neglect after stroke consistently evaluated the app positively on the dimensions of motivation, satisfaction, and fun.

CONCLUSIONS

The Negami app represents a promising extension by adding AR to traditional exploration training for spatial neglect. Through participants' natural interaction with the physical surrounding environment during playful tasks, side effects as symptoms of cybersickness are minimized and patients' motivation appeared to markedly increase. The use of AR in cognitive rehabilitation programs and the treatment of spatial neglect seems promising and should receive further investigation.

Study protocol of transcranial electrical stimulation at alpha frequency applied during rehabilitation: A randomized controlled trial in chronic stroke patients with visuospatial neglect

BACKGROUND

A frequent post stroke disorder in lateralized attention is visuospatial neglect (VSN). As VSN has a strong negative impact on recovery in general and independence during daily life, optimal treatment is deemed urgent. Next to traditional stroke treatment, non-invasive brain stimulation offers the potential to facilitate stroke recovery as a complementary approach. In the present study, visual scanning training (VST; the current conventional treatment) will be combined with transcranial alternating current stimulation (tACS) to evaluate the additive effects of repeated sessions of tACS in combination with six-weeks VST rehabilitation.

METHODS

In this double-blind randomized placebo-controlled intervention study (RCT), we will compare the effects of active tACS plus VST to sham (placebo) tACS plus VST, both encompassing 18 VST training sessions, 40 minutes each, during 6 weeks. Chronic stroke patients with VSN (> 6 months post-stroke onset) are considered eligible for study participation. In total 22 patients are needed for the study. The primary outcome is change in performance on a cancellation task. Secondary outcomes are changes in performance on a visual detection task, two line bisection tasks, and three measures to assess changes in activities of daily living. Assessment is at baseline, directly after the first and ninth training session, after the last training session (post training), and 1 week and 3 months after termination of the training (follow-up).

DISCUSSION

If effective, a tACS-VST rehabilitation program could be implemented as a treatment option for VSN.

TRIAL REGISTRATION

ClinicalTrials.gov ; registration number: NCT05466487; registration date: July 18, 2022 retrospectively registered; https://clinicaltrials.gov/ct2/show/NCT05466487.

On line bisection: Validity and reliability of online measures of pseudoneglect

This study assessed pseudoneglect using line bisection and perceptual landmark tasks in two matched online sessions. Line bisection bias was characterized by the traditional measure of Directional Bisection Error (DBE), and by Endpoint Weightings Bias (EWB), derived from an "endpoint weightings" analysis, made possible by the independent manipulation of left and right endpoints. EWB is proposed to index the relative attentional allocation to the two ends of the line. The expected leftward bias (pseudoneglect) was found, with larger effect sizes for EWB (d = -0.34 in both sessions) than for DBE (-0.22 in Session 1 and -0.14 in Session 2). Although EWB was slightly less reliable than DBE, it was more sensitive to pseudoneglect, and the endpoint weightings method has further advantages, including the option of an additional measure of non-lateralized attention. A substantial proportion of participants had difficulty following the instructions for the landmark task, which highlights the need for clear instructions and performance checks for this task. This study shows that line bisection can be used to measure pseudoneglect online, and provides grounds to suggest that the task should routinely include the independent manipulation of left and right endpoints, so that an endpoint weightings analysis can be performed.

Endpoints and viewpoints on spatial neglect

In this issue of the Journal of Neuropsychology, Abe and Ishiai (2022) report an experiment designed to probe the subjective experience of line bisection in neglect. A re-analysis of their data can also offer insights into how best to characterise neglect performance for this and other tasks. We show that sensitive measures of neglect can be obtained by quantifying the difference in the influence (or 'weighting') that each endpoint has on the response. The right endpoint is dramatically more influential than the left in people with neglect performing line bisection and endpoint reproduction tasks. This supports the view that neglect may limit the ability to simultaneously represent two locations, so that the response is determined primarily with respect to the right endpoint. We also discuss Abe and Ishiai's conclusion that bisection responses in neglect are accompanied by the subjective experience of a complete line extending equally to either side of the chosen midpoint.

The mobility assessment course: A ready-to-use dynamic measure of visuospatial neglect

The Mobility Assessment Course (MAC) is a tool to measure visuospatial neglect in a dynamic fashion. Although the MAC has been shown to dissociate between patients with and without neglect, it remains unclear whether it is applicable in clinical settings. We evaluated the MAC regarding its (1) feasibility as a diagnostic tool as part of standard care, (2) construct validity, and (3) underlying constructs and potential confounders. A consecutive sample of stroke patients admitted to inpatient rehabilitation completed the MAC, shape cancellation, line bisection, and/or Catherine Bergego Scale (CBS) as part of the standard assessment. To assess feasibility, we computed the percentage of patients who completed the MAC. Construct validity was tested by evaluating MAC performance between patients with and without neglect and controls. Finally, a regression analysis was conducted to assess underlying constructs and potential confounders of MAC performance (i.e., level of mobility and lesion side). The MAC was completed by 82% of patients (N = 182/223; of whom 145 completed all tasks). Patients with neglect performed worse on the MAC (indicating more severe neglect) compared to patients without neglect and controls. The MAC had a lower sensitivity and higher specificity than paper-and-pencil tasks and the CBS. Performance on shape cancellation, line bisection, and CBS were predictors of MAC performance. Level of mobility and lesion side did not predict MAC scores, indicating that these factors do not confound its reliability. To conclude, the MAC is an easy-to-implement tool to evaluate neglect in a dynamic manner, which can be administered in addition to conventional paper-and-pencil tasks.

Mental representation of a line when patients with left unilateral spatial neglect bisect it: A study with an endpoint reproduction task

Patients with left unilateral spatial neglect (USN) typically place the subjective midpoint to the right of the objective centre. Based on the previous findings (e.g., Ishiai et al. 1989, Brain, 112, 1485), we hypothesized that the patients with left USN may see the representational image of a line that extends equally towards either side of the subjective midpoint depending not upon the information about the leftward extent. The present study tested whether patients with left USN would place the subjective midpoint at the centre of their mental representation of the line. The participants were 10 patients with left USN and 10 neurologically healthy controls. We devised a new 'endpoint reproduction task' using a computer display with a touch panel to seek the representational image when patients with left USN bisect lines and asked the participants to reproduce the location of the right or left endpoint after bisecting lines. The results showed that the representational image of the bisected line depends primarily on the location of the objective right endpoint, not on the location of the objective left endpoint in space. The analyses of the estimated right and left representational extents confirmed our hypotheses that patients with left USN would bisect a line seeing the representational line image that centred across their subjective midpoint. We believe that the findings of the present study with the use of the endpoint reproduction task will contribute to a better understanding of the visuospatial process underlying line bisection of patients with left USN.

Congruent movement training as a rehabilitation method to ameliorate symptoms of neglect-proof of concept

Stroke patients with visuospatial neglect (VSN) have difficulties responding to visual information located in the contralesional hemifield, affecting many daily life activities (ADL) such as eating, reading and mobility. Visual Scanning Therapy (VST) is widely used in clinical practice to ameliorate symptoms of VSN. Yet, not all patients benefit from this training and many training sessions are needed in order to achieve stable results. One potentially promising improvement to the VST is based on the theory that different effectors of the motor systems (e.g., eyes, hands) independently allocate attention during the programming of the movement (i.e., Pre Motor Theory of Attention (PMT)). Here, we studied this direct implementation of the PMT and tested whether a congruent movement training (CMT: congruent -i.e., executed at the same time to the same location-eye and pointing movements) is more effective to attenuate symptoms of neglect compared to VST. This study can be seen as a proof of concept. Attenuation of neglect symptoms was found in the CMT group after just 5 h of training in the subacute phase of neglect. In contrast, no training effects were found in the VST group. These findings indicate the potential of CMT which is a minimal -yet crucial-upgrade of the standard VST protocol that can be easily implemented in the clinic.

Exploring the relationship between impaired illness awareness and visuospatial inattention in patients with schizophrenia

Anosognosia, described as impairment in an individual's ability to perceive and understand their illness, and visuospatial inattention commonly co-occur as a result of structural brain lesions in the right posterior parietal area. Anosognosia or impaired illness awareness is a common feature of schizophrenia that contributes to medication nonadherence and poor clinical outcomes. A recent pilot study suggests patients with impaired illness awareness have a rightward visuospatial bias. We aimed to examine this relationship in a large sample of patients. This study consisted of 106 patients with schizophrenia spectrum disorder (henceforth, schizophrenia) and 20 healthy controls. Visuospatial attention was assessed using the line bisection test (LBT). Illness awareness was assessed using the VAGUS self-report version. A Welch's t-test was used to examine differences in LBT scores between patients with schizophrenia and healthy controls. Correlation analyses between LBT and VAGUS scores were performed in patients with schizophrenia. For exploratory purposes, intra-subject reliability of the LBT was also examined using a two-way mixed intra-class correlation coefficient (ICC). There were no differences in LBT scores between patients with schizophrenia and healthy controls. In patients, there were no associations between LBT and VAGUS scores. ICCs between two consecutively acquired LBTs were 0.92 (95% CI: 0.81-0.96) in patients with schizophrenia and 0.93 (95% CI: 0.81-0.97) in healthy controls. Our results, using a reliable measure, did not support our previous preliminary finding that suggested a relationship between impaired illness awareness and visuospatial bias in patients with schizophrenia. Future studies should consider more sensitive visuospatial attention tasks when testing this hypothesis.

How does the number of targets affect visual search performance in visuospatial neglect?

INTRODUCTION

Impairments in visual search are a common symptom in visuospatial neglect (VSN). The severity of the lateralized attention bias in visual search tasks can vary depending on the number of distractors: the more distractors, the more targets are missed. However, little is known about how the number of targets affect search performance in VSN. The aim of the current study was to examine the effect of the number of targets on hit rate in VSN.

METHODS

We included 23 stroke patients with right-brain damage and VSN, 55 with right-brain damage without VSN, and 49 with left-brain damage without VSN, all admitted for inpatient rehabilitation. In a visual search task, patients had to find and tap targets, presented along with non-targets. The location and number of targets varied from trial to trial, allowing the evaluation of the effects of number and location of targets on hit rate.

RESULTS

VSN patients detected a lower percentage of targets when more targets were present. For patients with right-brain damage without VSN, adding targets only reduced the hit rate of the most contralesional target. No effect of number of targets on hit rate was seen in patients with left-brain damage. Additionally, VSN patients found less contralesional targets than ipsilesional targets, made more delayed revisits, and had an initial rightward bias when compared to the other groups. There were no differences in search time, search consistency, or immediate revisits between groups. There was a moderate positive relation between the hit rate asymmetry score in our search task and conventional paper-and-pencil VSN tasks, and neglect behavior in daily life.

CONCLUSIONS

In VSN patients, a higher number of targets reduces the hit rate. The reduced hit rate in visual search evoked by additional targets should be taken into account when assessing visual search in VSN.

Disconnection somewhere down the line: Multivariate lesion-symptom mapping of the line bisection error

Line Bisection is a simple task frequently used in stroke patients to diagnose disorders of spatial perception characterized by a directional bisection bias to the ipsilesional side. However, previous anatomical and behavioural findings are contradictory, and the diagnostic validity of the line bisection task has been challenged. We hereby aimed to re-analyse the anatomical basis of pathological line bisection by using multivariate lesion-symptom mapping and disconnection-symptom mapping based on support vector regression in a sample of 163 right hemispheric acute stroke patients. In line with some previous studies, we observed that pathological line bisection was related to more than a single focal lesion location. Cortical damage primarily to right parietal areas, particularly the inferior parietal lobe, including the angular gyrus, as well as damage to the right basal ganglia contributed to the pathology. In contrast to some previous studies, an involvement of frontal cortical brain areas in the line bisection task was not observed. Subcortically, damage to the right superior longitudinal fasciculus (I, II and III) and arcuate fasciculus as well as the internal capsule was associated with line bisection errors. Moreover, white matter damage of interhemispheric fibre bundles, such as the anterior commissure and posterior parts of the corpus callosum projecting into the left hemisphere, was predictive of pathological deviation in the line bisection task.

The reliability of pseudoneglect is task dependent

Bisection tasks that require individuals to identify the midpoint of a line are often used to assess the presence of biases to spatial attention in both healthy and patient populations. These tasks have helped to uncover a phenomenon called pseudoneglect, a bias towards the left-side of space in healthy individuals. First identified in the tactile domain, pseudoneglect has been subsequently demonstrated in other sensory modalities such as vision. Despite this, the specific reliability of pseudoneglect within individuals across tasks and time has been investigated very little. In this study, we investigated the reliability of response bias within individuals across four separate testing sessions and during three line bisection tasks: landmark, line bisection and tactile rod bisection. Strong reliability was expected within individuals across task and session. Pseudoneglect was found when response bias was averaged across all tasks, for the entire sample. However, individual data showed biases to both left and right, with some participants showing no clear bias, demonstrating individual differences in bias. Significant, cross-session within-individual reliability was found for the landmark and tactile rod bisection tasks respectively, but no significant reliability was observed for the line bisection task. These results highlight the inconsistent nature of pseudoneglect within individuals, particularly across sensory modality. They also provide strong support for the use of the landmark task as the most reliable measure of pseudoneglect.

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Reliability of pseudoneglect was assessed across 4 sessions and 3 tasks.

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The landmark task was the most reliable test for pseudoneglect across sessions.

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Responses to line bisection and tactile rod were less reliable across sessions.

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Responses to different bisection tasks in the same individuals were not reliable.

Non-Spatial Impairments Affect False-Positive Neglect Diagnosis Based on Cancellation Tasks

OBJECTIVE

To diagnose egocentric neglect after stroke, the spatial bias of performance on cancellation tasks is typically compared to a single cutoff. This standard procedure relies on the assumption that the measurement error of cancellation performance does not depend on non-spatial impairments affecting the total number of cancelled targets. Here we assessed the impact of this assumption on false-positive diagnoses.

METHOD

We estimated false positives by simulating cancellation data using a binomial model. Performance was summarised by the difference in left and right cancelled targets (R-L) and the Centre of Cancellation (CoC). Diagnosis was based on a fixed cutoff versus cutoffs adjusted for the total number of cancelled targets and on single test performance versus unanimous or proportional agreement across multiple tests. Finally, we compared the simulation findings to empirical cancellation data acquired from 651 stroke patients.

RESULTS

Using a fixed cutoff, the rate of false positives depended on the total number of cancelled targets and ranged from 10% to 30% for R-L scores and from 10% to 90% for CoC scores. The rate of false positives increased even further when diagnosis was based on proportional agreement across multiple tests. Adjusted cutoffs and unanimous agreement across multiple tests were effective at controlling false positives. For empirical data, fixed versus adjusted cutoffs differ in estimation of neglect prevalence by 13%, and this difference was largest for patients with non-spatial impairments.

CONCLUSIONS

Our findings demonstrate the importance of considering non-spatial impairments when diagnosing neglect based on cancellation performance.

Peripersonal and extrapersonal visuospatial neglect in different frames of reference: A brain lesion-symptom mapping study

INTRODUCTION

Visuospatial neglect can occur in peripersonal and extrapersonal space. The dorsal visual pathway is hypothesized to be associated with peripersonal, and the ventral pathway with extrapersonal neglect. We aimed to evaluate neural substrates of peripersonal versus extrapersonal neglect, separately for egocentric and allocentric frames of reference.

METHODS

This was a retrospective study, including stroke patients admitted for inpatient rehabilitation. Approximately 1 month post-stroke onset, computerized cancellation (egocentric) and bisection tasks (egocentric and allocentric) were administered at 30 cm and 120 cm. We collected CT or MRI scans and performed voxel-based lesion-symptom mapping for the cancellation, and subtraction analyses for the line bisection task.

RESULTS

We included 98 patients for the cancellation and 129 for the bisection analyses. The right parahippocampal gyrus, hippocampus, and thalamus were associated with egocentric peripersonal neglect as measured with cancellation. These areas were also associated with extrapersonal neglect, together with the right superior parietal lobule, angular gyrus, supramarginal gyrus, lateral occipital cortex, planum temporale and superior temporal gyrus. Lesions in the right parietal, temporal and frontal areas were associated with both peripersonal and extrapersonal egocentric neglect as measured with bisection. For allocentric neglect no clear pattern of associated brain regions was observed.

DISCUSSION

We found right hemispheric anatomical correlates for peripersonal and extrapersonal neglect. However, no brain areas were uniquely associated with peripersonal neglect, meaning we could not conclusively verify the ventral/dorsal hypothesis. Several areas were uniquely associated with egocentric extrapersonal neglect, suggesting that these brain areas can be specifically involved in extrapersonal, but not in peripersonal, attention processes.

Weight and see: Line bisection in neglect reliably measures the allocation of attention, but not the perception of length

Line bisection has long been a routine test for unilateral neglect, along with a range of tests requiring cancellation, copying or drawing. However, several studies have reported that line bisection, as classically administered, correlates relatively poorly with the other tests of neglect, to the extent that some authors have questioned its status as a valid test of neglect. In this article, we re-examine this issue, employing a novel method for administering and analysing line bisection proposed by McIntosh et al. (2005). We report that the measure of attentional bias yielded by this new method (EWB) correlates significantly more highly with cancellation, copying and drawing measures than the classical line bisection error measure in a sample of 50 right-brain damaged patients. Furthermore when EWB was combined with a second measure that emerges from the new analysis (EWS), even higher correlations were obtained. A Principal Components Analysis found that EWB loaded highly on a major factor representing neglect asymmetry, while EWS loaded on a second factor which we propose may measure overall attentional investment. Finally, we found that tests of horizontal length and size perception were related poorly to other measures of neglect in our group. We conclude that this novel approach to interpreting line bisection behaviour provides a promising way forward for understanding the nature of neglect.

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We used novel measures of attentional allocation to study line bisection behaviour in 50 right-brain damaged patients.

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These measures were more sensitive to neglect than was directional bisection error, and they correlated more highly with other core tests of neglect.

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We propose that one measure (EWB) reflects a lateral bias of attention, and the other measure (EWS) reflects overall attention.

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Perceptual biases on size-matching and landmark tasks did not correlate highly with line bisection, or any other core tests of neglect.

The end of the line: Antagonistic attentional weightings in unilateral neglect

The line bisection task is widely used in the study of neglect. Some years ago, McIntosh, Schindler, Birchall, & Milner (2005) proposed a radical reframing of this ubiquitous task. Rather than using the traditional measure of directional bisection error, they quantified the sensitivities of the response to the changing locations of the left and right endpoints of the line, expressing these as 'endpoint weightings'. A novel prediction generated from their analysis was that manipulations increasing attention to the left end of the line should cause an increase in the left endpoint weighting and a corresponding reduction in the right endpoint weighting. The present study fulfilled this prediction, using a forced-report cueing method in a group of 12 patients with left neglect. The data confirm an antagonistic relationship between endpoint weightings, consistent with the idea that they represent the sharing of a finite resource. It is argued that the endpoint weightings model of line bisection offers a sensitive and uniquely useful framework for studying competitive lateral biases of attention in neglect, and may also provide insight into non-lateralised attentional impairments.

Look where you're going! Perceptual attention constrains the online guidance of action

Action guidance, like perceptual discrimination, requires selective attention. Perception is enhanced at the target of a reaching movement, but it is not known whether selecting an object for perception reciprocally prioritises it for action. Two theoretical frameworks, the premotor theory and the Visual Attention Model, predict that this reciprocal relation should hold. We tested the influence of perceptual attention on the online control of reaching. In Experiment 1, participants attended covertly to a flanker on one or other side of a fixated target, prior to reaching for that target, which occasionally jumped, after reach onset, to the attended or non-attended side. Participants corrected their reaches for almost all target jumps. In Experiment 2, we required covert monitoring of the flanker during reaching. This concurrent perceptual task globally reduced correction behaviour, indicating that perception and action share a common attentional resource. Corrections were especially unlikely toward the attended side. This is explained by assuming that perceptual attention primed an action toward the attended location and that the participant inhibited this primed action. The data thus imply that perceptual selection constrains online action guidance, as predicted by the premotor theory and the VAM. We further argue that the fact that participants can inhibit a location within the action system but simultaneously maintain its prioritisation for perceptual monitoring, is easier to reconcile with the VAM than with the premotor theory.

Representational pseudoneglect: a review

Pseudoneglect, the tendency to be biased towards the left-hand side of space, is a robust and consistent behavioural observation best demonstrated on the task of visuospatial line bisection, where participants are asked to centrally bisect visually presented horizontal lines at the perceived centre. A number of studies have revealed that a representational form of pseudoneglect exists, occurring when participants are asked to either mentally represent a stimulus or explore a stimulus using touch in the complete absence of direct visuospatial processing. Despite the growing number of studies that have demonstrated representational pseudoneglect there exists no current and comprehensive review of these findings and no discussion of a theoretical framework into which these findings may fall. An important gap in the current representational pseudoneglect literature is a discussion of the developmental trajectory of the bias. The focus of the current review is to outline studies that have observed representational pseudoneglect in healthy participants, consider a theoretical framework for these observations, and address the impact of lifespan factors such as cognitive ageing on the phenomenon.

A circle-monitor for computerised assessment of visual neglect in peripersonal space

Current assessment of visual neglect involves paper-and-pencil tests or computer-based tasks. Both have been criticised because of their lack of ecological validity as target stimuli can only be presented in a restricted visual range. This study examined the user-friendliness and diagnostic strength of a new "Circle-Monitor" (CM), which enlarges the range of the peripersonal space, in comparison to a standard paper-and-pencil test (Neglect-Test, NET).

METHODS

Ten stroke patients with neglect and ten age-matched healthy controls were examined by the NET and the CM test comprising of four subtests (Star Cancellation, Line Bisection, Dice Task, and Puzzle Test).

RESULTS

The acceptance of the CM in elderly controls and neglect patients was high. Participants rated the examination by CM as clear, safe and more enjoyable than NET. Healthy controls performed at ceiling on all subtests, without any systematic differences between the visual fields. Both NET and CM revealed significant differences between controls and patients in Line Bisection, Star Cancellation and visuo-constructive tasks (NET: Figure Copying, CM: Puzzle Test). Discriminant analyses revealed cross-validated assignment of patients and controls to groups was more precise when based on the CM (hit rate 90%) as compared to the NET (hit rate 70%).

CONCLUSION

The CM proved to be a sensitive novel tool to diagnose visual neglect symptoms quickly and accurately with superior diagnostic validity compared to a standard neglect test while being well accepted by patients. Due to its upgradable functions the system may also be a valuable tool not only to test for non-visual neglect symptoms, but also to provide treatment and assess its outcome.

Pleasant music improves visual attention in patients with unilateral neglect after stroke

OBJECTIVE

To investigate whether listening to pleasant music improves visual attention to and awareness of contralesional stimuli in patients with unilateral neglect after stroke.

METHODS

A within-subject design was used with 19 participants with unilateral neglect following a right hemisphere stroke. Participants were tested in three conditions (pleasant music, unpleasant music and white noise) within 1 week. All musical pieces were chosen by the participants. In each condition, participants were asked to complete three sub-tests of the Behavioural Inattention Test (the Star Cancellation Test, the Line Bisection Test and the Picture Scanning test) and a visual exploration task with everyday scenes. Eye movements in the visual exploration task were recorded simultaneously. Mood and arousal induced by different auditory stimuli were assessed using visual analogue scales, heart rate and galvanic skin response.

RESULTS

Compared with unpleasant music and white noise, participants rated their moods as more positive and arousal as higher with pleasant music, but also showed significant improvement on all tasks and eye movement data, except the Line Bisection Test.

CONCLUSION

The findings suggest that pleasant music can improve visual attention in patients with unilateral neglect after stroke. Additional research using randomized controlled trials is required to validate these findings.

A virtual reality test battery for assessment and screening of spatial neglect

BACKGROUND

There is a need for improved screening methods for spatial neglect.

AIM

To construct a VR-test battery and evaluate its accuracy and usability in patients with acute stroke.

METHOD

VR-DiSTRO consists of a standard desktop computer, a CRT monitor and eye shutter stereoscopic glasses, a force feedback interface, and software, developed to create an interactive and immersive 3D experience. VR-tests were developed and validated to the conventional Star Cancellation test, Line bisection, Baking Tray Task (BTT), and Visual Extinction test. A construct validation to The Rivermead Behavioral Inattention Test, used as criterion of visuospatial neglect, was made. Usability was assessed according to ISO 9241-11.

RESULTS

Thirty-one patients with stroke were included, 9/31 patients had neglect. The sensitivity was 100% and the specificity 82% for the VR-DiSTRO to correctly identify neglect. VR-BTT and VR-Extinction had the highest correlation (r² = 0.64 and 0.78), as well as high sensitivity and specificity. The kappa values describing the agreement between traditional neglect tests and the corresponding virtual reality test were between 0.47-0.85. Usability was assessed by a questionnaire; 77% reported that the VR-DiSTRO was 'easy' to use. Eighty-eight percent reported that they felt 'focused', 'pleased' or 'alert'. No patient had adverse symptoms. The test session took 15 min.

CONCLUSIONS

The VR-DiSTRO quickly and with a high accuracy identified visuospatial neglect in patients with stroke in this construct validation. The usability among elderly patients with stroke was high. This VR-test battery has the potential to become an important screening instrument for neglect and a valuable adjunct to the neuropsychological assessment.

Dissecting the component deficits of perceptual imbalance in visual neglect: evidence from horizontal-vertical length comparisons

INTRODUCTION

Signs of left unilateral neglect often occur after damage to the right hemisphere and entail a left-right imbalance in stimulus processing. Typically, neglect patients deviate rightward when bisecting lines. An underestimation of the left portion of the line and/or a right overestimation could explain this effect.

METHODS

Here we dissected their respective contribution by asking participants to compare a vertical segment to a horizontal segment, either on the left or on the right. We also tested whether neglect patients exhibited the symmetry law, whereby normal participants underestimate symmetrically bisected lines as compared to asymmetrically bisected lines.

RESULTS

Controls and patients underestimated symmetric figures. Depending on the degree of left-right horizontal competition, neglect patients underestimated left-sided stimuli or overestimated right-sided stimuli.

CONCLUSIONS

We concluded that two independent deficits contribute to neglect signs: a deficit in attentional orienting to the left, which can be worsened by left hemianopia, perhaps depending on impaired functioning of right-hemisphere attentional networks, and a tendency for attention to be captured by right-sided stimuli, possibly resulting from the activity of an isolated left hemisphere. Finally, the symmetry law was preserved in neglect patients, and thus appears to be driven by pre-attentive mechanisms.

Spatial neglect and attention networks

Unilateral spatial neglect is a common neurological syndrome following predominantly right hemisphere injuries and is characterized by both spatial and non-spatial deficits. Core spatial deficits involve mechanisms for saliency coding, spatial attention, and short-term memory and occur in conjunction with nonspatial deficits that involve reorienting, target detection, and arousal/vigilance. We argue that neglect is better explained by the dysfunction of distributed cortical networks for the control of attention than by structural damage of specific brain regions. Ventral lesions in right parietal, temporal, and frontal cortex that cause neglect directly impair nonspatial functions partly mediated by a ventral frontoparietal attention network. Structural damage in ventral cortex also induces physiological abnormalities of task-evoked activity and functional connectivity in a dorsal frontoparietal network that controls spatial attention. The anatomy and right hemisphere dominance of neglect follow from the anatomy and laterality of the ventral regions that interact with the dorsal attention network.

The amusic brain: lost in music, but not in space

Congenital amusia is a neurogenetic disorder of music processing that is currently ascribed to a deficit in pitch processing. A recent study challenges this view and claims the disorder might arise as a consequence of a general spatial-processing deficit. Here, we assessed spatial processing abilities in two independent samples of individuals with congenital amusia by using line bisection tasks (Experiment 1) and a mental rotation task (Experiment 2). Both amusics and controls showed the classical spatial effects on bisection performance and on mental rotation performance, and amusics and controls did not differ from each other. These results indicate that the neurocognitive impairment of congenital amusia does not affect the processing of space.

Rightward collisions and their association with pseudoneglect

Whereas right parietal damage can result in left hemineglect, the general population shows a subtle neglect of the right hemispace-known as pseudoneglect. A recent study has demonstrated that people collide to the right more often and attributed this bias to pseudoneglect. [Nicholls, M. E. R., Loftus, A., Meyer, K., & Mattingley, J.B. (2007). Things that go bump in the right: The effect of unimanual activity on rightward collisions. Neuropsychologia, 45, 1122-1126]. Nicholls examined the effect of unimanual activation by requiring participants to fire projectiles at a target whilst walking and found that the rightward bias was exaggerated or reversed when the left and right hands were active, respectively. However, the act of aiming at a target may have inadvertently biased walking trajectory to the right. The current study addressed this issue by requiring participants (n=149) to walk through a narrow doorway three times whilst entering text into a phone using the (a) left, (b) right or (c) both hands. Despite the fact that entering text into a phone should produce no rightward bias, participants bumped to the right more often. Unlike previous research, no effect of unimanual activation was observed. This lack of effect was attributed to the smaller hand movements for entering numbers compared to firing a toy gun. Finally, this study showed an association for the first time between biases in observable bumping and line bisection performance-suggesting that unilateral bumping is related to pseudoneglect.

Line bisection in left neglect: the importance of starting right

When marking the subjective midpoint of a horizontal line, patients with left unilateral neglect typically deviate rightward. Different accounts of this pattern of performance refer either to a biased competition between the two hemi-segments of the line, with the right part being subjectively perceived as longer than the left part, or to a distortion of a cognitive representation of space, with spatial coordinates progressively relaxing from the right to the left. These accounts make different predictions about the role of the right part of the line, which is crucial in the biased competition account, but less important in the distortion account. To test these predictions, we asked participants to set the endpoints and the centre of perceived and imaginary lines. Contrary to previous studies, we controlled for the direction of performance of the endpoint task, with left-to-right trials and right-to-left trials being performed in separate blocks. Five patients with right-hemisphere lesions and left neglect demonstrated the typical asymmetries when a right-sided stimulus (segment or endpoint) was present, but showed either normal performance or a reversed (leftward) bias while setting the endpoints and the centre of an imaginary line starting from the left side, when no right-sided visual stimulus was present until completion of each trial. We concluded that the right-sided portion of the line has a crucial importance in determining patients' rightward deviations in line bisection, consistent with the biased competition hypothesis and with neurocognitive models of attentional orienting.

Pseudoneglect and neglect for mental alphabet lines

While patients with right parietal damage neglect the left side of stimuli, the intact-brain population shows a slight neglect of the right side--known as pseudoneglect. Although pseudoneglect occurs for physical stimuli, it is not certain whether the bias extends to mental representations. To investigate this issue, we examined spatial distortions in the representation of length for mental alphabet lines, which are thought to have a left-to-right arrangement. In Expt. 1, participants (n=10) were presented with letter strings (e.g. C_H_P) and estimated whether the letter length was greater on the left or right side of the inner-letter. The strings were presented simultaneously along a line or sequentially in the centre of the screen in either an ascending (i.e. A-Z) or descending (i.e. Z-A) sequence. Participants reliably overestimated the length on the left regardless of presentation mode. In Expt. 2, participants (n=20) judged whether the inner-letter was the true centre. Responses were biased such that inner-letters shifted to the left of true centre were perceived to be the centre. Combined, both studies demonstrate that the length on left side of the mental alphabet line is overestimated relative to the right. In Expt. 3, a reversal of the bias towards the right was found for a group of neglect patients. The data demonstrate that letters have a left-to-right mental representation and that the left side of this representation is overrepresented in a manner similar to the overestimation associated with pseudoneglect for physical stimuli.

Things that go bump in the right: The effect of unimanual activity on rightward collisions

Patients with right parietal damage and spatial neglect ignore the leftward features of their environment - causing them to bump into the left-side of doorways. In contrast, the normal population shows a mild attentional bias towards the left. Self-report measures show more collisions to the right in everyday settings. We sought to obtain a quantitative measure of lateralised bumping in a laboratory setting. Participants (n=276) walked through a narrow doorway and the experimenter recorded collisions. To investigate the association between bumping and paper-and-pencil tests of pseudoneglect, a line bisection task was administered. Unilateral activation of the hemispheres has been found to ameliorate the effects of spatial neglect. We investigated the effect of activation by asking participants to move their left-, right- or both-hands as they walked. In the both hands condition, which acted as a baseline, there were more right bumps than left bumps. The rightward bias was exasperated when the left hand moved, presumably because this movement activated the right hemisphere. In contrast, there were more left bumps when the right hand moved. The results demonstrate that bumping is not random and that we collide with the right side more often. Biases in bumping, however, were not related to biases in line bisection. The effect of hand-movement demonstrates that bumping is brought about by an imbalance of activation between the hemispheres.

The eyes have it: Oculomotor exploration and line bisection in neglect

In this issue of Cortex, Ishiai et al. (2006) report the eye movements of patients with left neglect during the bisection of lines of different lengths. This is the latest in a series of papers from Ishiai's group, which form an important corpus of data on the oculomotor behaviour of neglect patients during line bisection and related tasks. In this article, I argue that these data should critically constrain theoretical models of bisection errors in neglect, but that these constraints have been applied rarely in practice. First, I briefly introduce bisection behaviour in neglect and describe some of the models proposed to account for its character. I then consider the implications for these models of Ishiai and colleagues' observations. Finally, I outline a novel view of the bisection task that is more compatible with their observations.