Temporal order judgements as a sensitive measure of the spatial bias in patients with visuospatial neglect

Visuospatial neglect is not a unitary phenomenon, but can be better considered a syndrome, consisting of a multitude of different spatial and non‐spatial components. In this study, we used a temporal order judgement (TOJ) test in a large sample of stroke patients (n = 73) to scrutinize the contribution of a spatial bias to the performance on shape cancellation and line bisection tests. In the TOJ test, patients were presented with two elements, one in each visual field, after which the one needed to indicate which of the two elements was presented earlier. For each visual field, the presentation of the stimuli was determined by a staircase procedure where the interval between the two stimuli was determined by the performance of the patient. Results indicated that the strength of the spatial bias was strongly correlated with an object cancellation test, but not with a line bisection test. We argue that these findings are explained by differences in the extent to which a spatial bias determines performance on both tasks: In contrast to shape cancellation tests, successful performance on line bisection tests depends primarily on an object‐based, allocentric representation of space, unrelated to any spatial bias in the detection of elements in the contralesional visual field.     

Visuospatial Neglect: The Ultimate Deconstruction?

Unilateral visuospatial neglect is now widely acknowledged to be a highly heterogeneous condition: The overt manifestations of visual neglect can vary as a function of task, spatial domain, and mode of response (at least). Double dissociations (sometimes of the strong form) have already been reported between most of the components of what was originally thought to be a relatively stable construct within the visual modality. Nonetheless, throughout successive fractionations of neglect, reported cases of bidirectional task-specific neglect after unilateral brain damage are rare. We now report two such cases. After right hemisphere stroke, the first patient reliably showed severe left neglect on cancellation but right neglect on line bisection. After left hemisphere stroke, the second case showed right neglect on cancellation but left neglect on line bisection. Extensive investigation of case 1 confirmed our previous conjecture that the crucial distinction between these tasks lies in the presence or the absence of an overt target. In contrast to cancellation, line bisection demands the internal computation of the location of the “target” (the midpoint), followed by executing a motor response toward the precise location of that “imaginary” midpoint. The relative attentional and premotor contributions of the intact and damaged hemispheres to these forms of bidirectional neglect are also assessed.     

Representational neglect for words as revealed by bisection tasks

In the present study, we showed that a representational disorder for words can dissociate from both representational neglect for objects and neglect dyslexia. This study involved 14 brain-damaged patients with left unilateral spatial neglect and a group of normal subjects. Patients were divided into four groups based on presence of left neglect dyslexia and representational neglect for non-verbal material, as evaluated by the Clock Drawing test. The patients were presented with bisection tasks for words and lines. The word bisection tasks (with words of five and seven letters) comprised the following: (1) representational bisection: the experimenter pronounced a word and then asked the patient to name the letter in the middle position; (2) visual bisection: same as (1) with stimuli presented visually; and (3) motor bisection: the patient was asked to cross out the letter in the middle position. The standard line bisection task was presented using lines of different length. Consistent with the literature, long lines were bisected to the right and short lines, rendered comparable in length to the words of the word bisection test, deviated to the left (crossover effect). Both patients and controls showed the same leftward bias on words in the visual and motor bisection conditions. A significant difference emerged between the groups only in the case of the representational bisection task, whereas the group exhibiting neglect dyslexia associated with representational neglect for objects showed a significant rightward bias, while the other three patient groups and the controls showed a leftward bisection bias. Neither the presence of neglect alone nor the presence of visual neglect dyslexia was sufficient to produce a specific disorder in mental imagery. These results demonstrate a specific representational neglect for words independent of both representational neglect and neglect dyslexia.     

Representational bias does not affect bisection of lines with a pictorially or semantically defined top by patients with left hemispatial neglect

Normal subjects may have both representational and visual-based components determining bias in bisection of horizontal, vertical, and radial lines. The influence of these components is less clear in patients with neglect. We asked 25 patients with right hemisphere stroke and clinical features of neglect to bisect lines oriented horizontally, vertically, and radially above and below eye level. Objects including human silhouette figures, arrowheads, and the words 'TOP' and 'BOTTOM' were placed at either end of each line. These figures were presented either upright or upside down in some orientations, and presented rightward and leftward in other orientations, to pictorially or semantically define a "top" to each line independent of the actual top of the visual field. Patients demonstrated a rightward bias on all horizontal line bisections, with similar bias and greater magnitude than normal subjects. Patients also demonstrated visual-based biases on some of the vertical, radial down, and radial up lines presented. However, patients did not demonstrate a significant representational bias with any of the visual cues presented on any of the line orientations. Patients with acute right hemisphere stroke demonstrate a rightward bias when asked to perform line bisection in the horizontal line orientation, as well as an upward bias in vertical line bisection. The lack of representational bias in patients with neglect may be due to a greater degree of visual-based neglect as compared to representational neglect, or it may be due to an absence of representational bias in patients with right hemisphere stroke.     

Disruptions to number bisection after brain injury: Neglecting parts of the Mental Number Line or working memory impairments?

The aim of this study was to investigate the mechanisms underlying consistent directional number bisection bias in a chronic neuropsychological sample, not selected based on behaviour or lesion definitions. Patients completed a test battery that included measures of number bisection, line bisection, verbal working memory, visual-spatial working memory, egocentric neglect and allocentric neglect. Neither the neglect nor working memory measures were found to significantly correlate with number bisection. Furthermore, when outlier patients with very distinct number bisection biases were compared to patients who did not show any number bisection difficulties, no differences were found between the two groups on any of the other behavioural measures. We conclude that number bisection difficulties are not consistently based on any single deficit, be it neglect or working memory, and biases in number bisection should not be assumed to directly reflect problems in either of these areas.     

Radial bisection of words and lines in right‐brain‐damaged patients with spatial neglect

The bisection of lines positioned radially (with the two ends of the line close and far, with respect to the participant's body) has been less investigated than that of lines placed horizontally (with their two ends left and right, with respect to the body's midsagittal plane). In horizontal bisection, patients with left neglect typically show a rightward bias for both lines and words, greater with longer stimuli. As for radial bisection, available data indicate that neurologically unimpaired participants make a distal error, while results from right‐brain‐damaged patients with left spatial neglect are contradictory. We investigated the bisection of radially oriented words, with the prediction that, during bisection, linguistic material would be recoded to its canonical left‐to‐right format in reading, with the performance of neglect patients being similar to that for horizontal words. Thirteen right‐brain‐damaged patients (seven with left spatial neglect) and fourteen healthy controls were asked to manually bisect 40 radial and 40 horizontal words (5–10 letters), and 80 lines, 40 radial and 40 horizontal, of comparable length. Right‐brain‐damaged patients with spatial neglect exhibited a proximal bias in the bisection of short radial words, with the proximal part corresponding to the final right part of horizontally oriented words. This proximal error was not found in patients without neglect and healthy controls. For bisection, short radial words may be recoded to the canonical orthographic horizontal format, unveiling the impact of left neglect on radially oriented stimuli.     

Virtual reality pencil and paper tests for neglect: a protocol.

Hemispatial neglect is a common disorder that can occur after a lesion in the right hemisphere. Its main characterization is the difficulty in processing visual stimuli emanating from the space contralateral to the lesion. Pencil and paper tests (such as target cancellation, line bisection, or drawing copy) are used to diagnose neglect. We propose using virtual reality technology and haptic force feedback to enhance pencil and paper tests. Our system can track the patients' eye-gaze and their hand movements. Also, the efficiency of several techniques used to decrease the neglect in different sensory spaces are investigated.     

Simulating a lesion in a basis function model of spatial representations: comparison with hemineglect

The basis function theory of spatial representations explains how neurons in the parietal cortex can perform nonlinear transformations from sensory to motor coordinates. The authors present computer simulations showing that unilateral parietal lesions leading to a neuronal gradient in basis function maps can account for the behavior of patients with hemineglect, including (a) neglect in line cancellation and line bisection experiments; (b) neglect in multiple frames of reference simultaneously; (c) relative neglect, a form of what is sometime called object-centered neglect; and (d) neglect without optic ataxia. Contralateral neglect arises in the model because the lesion produces an imbalance in the salience of stimuli that is modulated by the orientation of the body in space. These results strongly support the basis function theory for spatial representations in humans and provide a computational model of hemineglect at the single-cell level.     

Virtual environment training system for rehabilitation of stroke patients with unilateral neglect: crossing the virtual street.

In this paper, we propose a system for training of stroke patients with unilateral neglect by using technology of virtual reality (VR). The proposed system is designed to compensate for unilateral neglect. This system contains the calibration of unilateral neglect and the training of this disease. The calibration procedure is implemented by aligning the virtual object at a subjective middle line. The training procedure is implemented by completing the missions that are used to keep the virtual avatar safe during crossing the street in a virtual environment. The results of this study show that the proposed system is effective to train unilateral neglect. The left to right ratio scores extracted from this system gradually decrease as the sessions of training are repeated. To validate the VR system parameters, the parameters are analyzed by correlation with those of traditional unilateral neglect assessment methods (such as the line bisection test and the cancellation test).     

Perceptual asymmetries in normal children and children with attention deficit/hyperactivity disorder

Perceptual asymmetries in normal right-handed children (7-12 years of age) and children with attention deficit/hyperactivity disorder (ADHD), combined type, were investigated using various chimeric stimuli in free-viewing conditions. In the face-matching task, participants indicated which of two symmetrical face chimeras more closely resembled the original; in the chimeric faces task, participants indicated which of a pair of faces appeared happier; and in the grey scales task participants indicated which of two shaded rectangles appeared to be darker overall. Leftward biases were found for normal children with no effects of age. Contrary to expectations, normal leftward biases were also found for ADHD children in the face-matching and the chimeric faces tasks; however, a significant leftward bias was not observed in the grey scales task. The absence of anomalous perceptual bias in ADHD children on these purely perceptual tasks, suggests that anomalous perceptual asymmetries observed in other tasks (line bisection and cancellation tasks) may have been confounded by the motor response, and/or the explicit spatial components of those tasks.     

Perceptual-attentional and motor-intentional bias in near and far space

Spatial bias demonstrated in tasks such as line-bisection may stem from perceptual-attentional (PA) "where" and motor-intentional (MI) "aiming" influences. We tested normal participants' line bisection performance in the presence of an asymmetric visual distracter with a video apparatus designed to dissociate PA from MI bias. An experimenter stood as a distractor to the left or right of a video monitor positioned in either near or far space, where participants viewed lines and a laser point they directed under (1) natural and (2) mirror-reversed conditions. Each trial started with the pointer positioned at either the top left or top right corner of the screen, and alternated thereafter. Data analysis indicated that participants made primarily PA leftward errors in near space, but not in far space. Furthermore, PA, but not MI, bias increased bilaterally in the direction of distraction. In contrast, MI, but not PA, bias was shifted bilaterally in the direction of startside. Results support the conclusion that a primarily PA left sided bias in near space is consistent with right hemisphere spatial attentional dominance. A bottom-up visual distractor specifically affected PA "where" spatial bias while top-down motor cuing influenced MI "aiming" bias.     

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.     

Impact of situational threat on the behavioral activation system

Previous research has indicated that individuals respond differently to difficult tasks, depending on whether the situational factors surrounding the task make the individual perceive it as a challenge or a threat. Distinct response patterns between these two stress responses have been identified and vary based on an individual’s personality traits. In keeping with this research, the current study examined how performance pressure-induced threat impacts the relationship between trait approach motivation and prefrontal cortex activation utilizing a simple line bisection task. Participants completed line bisection tasks before and after performing a difficult motor skill task under pressure intended to provoke a threat-based response. As expected, individuals with high levels of trait approach motivation showed a rightward line bisection bias at pretest absent in participants with low levels of trait approach motivation. However, in contrast to previous studies utilizing more challenge-based tasks that report consistent rightward line bisection bias in high approach motivation populations, the current study identified a shift towards a leftward line bisection bias after the study task. The results suggest that the inability to succeed under pressure caused high trait approach participants to temporarily lose their approach orientation due to threat response.     

The relationship between vertical stimulation and horizontal attentional asymmetries

The original aim was to examine the effect of perceived distance, induced by the Ponzo illusion, on left/right asymmetries for line bisection. In Experiment 1, university students (n?=?29) made left/right bisection judgements for lines presented in the lower or upper half of the screen against backgrounds of the Ponzo stimuli, or a baseline. While the Ponzo illusion had relatively little effect on line bisection, elevation in the baseline condition had a strong effect, whereby the leftward bias was increased for upper lines. Experiment 2 (n?=?17) eliminated the effect of elevation by presenting the line in the middle and moving the Ponzo stimuli relative to the line. Despite this change, the leftward bias was still stronger in the upper condition in the baseline condition. The final experiment (n?=?17) investigated whether upper/lower visual stimulation, which was irrelevant to the task, affected asymmetries for line bisection. The results revealed that a rectangle presented in the upper half of the screen increased the leftward line bisection bias relative to a baseline and lower stimulation condition. These results corroborate neuroimaging research, showing increased right parietal activation associated with shifts of attention into the upper hemispace. This increased right parietal activation may increase the leftward attentional bias—resulting in a stronger leftward bias for line bisection.     

Hemispheric control of spatial attention

According to the activation-orienting hypothesis the distribution of attention in space is biased in the direction contralateral to the more activated hemisphere. The present investigation tested this proposal and evaluated the nature of hemispheric differences in orienting control. Activation imbalance was produced by a unilateral visual stimulus. The distribution of attention was measured using a modified line bisection task in which subjects judged the location of an intersect on a tachistoscopically presented horizontal line. The first three experiments suggest that (a) attention is biased in the direction contralateral to the stimulated hemisphere, and (b) the biases do not depend on the task relevance or hemispatial position of the stimulus producing the activation imbalance. The final three experiments suggest that when orienting conflict is introduced the rightward bias becomes more robust than the leftward bias. The findings are consistent with the activation-orienting hypothesis. Each hemisphere generates a contralateral attentional bias and the rightward bias of the left hemisphere is stronger. The relevance of these findings to understanding unilateral neglect resulting from parietal damage is discussed.     

The effects of local and global processing demands on perception and action

The line-bisection task, adapted to utilise a wooden rod as the bisection stimulus, has revealed that patients with visuo-spatial neglect may be more accurate at bisection when asked to pick up the rod, compared to pointing to its centre. We recently reported that neurologically intact participants show a similar dissociation on this task-demonstrating a rightward bias when pointing to the centre, which was not present when grasping the rod by the centre. The current paper examined how pointing and grasping responses were affected by adapted rod-bisection tasks that emphasised local or global processing. In Experiment 1, 26 participants completed four rod-bisection tasks. The rods were compound stimuli and the participants directed to focus on either the local or global level. The results demonstrated that when participants focused on the global level, the previous dissociations found for pointing and grasping conditions were evident. However, the perception of centre did change when participants focused on the local level: both the pointing and grasping responses were rightward biased. In Experiment 2, 42 participants completed three bisection tasks which again emphasised either the local or global level, but in different sets of stimuli. The results of this task further support the findings in Experiment 1: the rightward bias in the local-bisection task was again evident and in addition, the global-bisection task resulted in no bias and no difference between the pointing and grasping bisections. These results demonstrate how task demands can similarly affect the pointing and grasping responses, and indicate that local and global processing may be involved in perception/action dissociations on rod bisection.     

Relationship maintenance and biases on the line bisection task: Attractive alternatives,asymmetrical cortical activity,and approach–avoidance motivation

People in long-term romantic relationships possess relationship maintenance mechanisms designed to protect against the temptation of desirable relationship alternatives. The current research examined the link between relationship maintenance mechanisms and an index of neurologically based approach/avoidance motivation. Participants completed a line bisection task that yields measures of asymmetric activity in the right and left frontal cortices; such activity is thought to reflect people's level of approach/avoidance motivation. Compared to single participants, participants in committed relationships displayed relatively less left visual field bias on the line bisection task (indicative of greater left frontal cortical activation and greater cognitive avoidance motivation) in response to available, attractive opposite-sex targets. Decreased left visual field bias was particularly pronounced among individuals with moderate levels of relationship commitment — those expected to display the highest levels of relationship maintenance. These findings provide insight into perceptual, motivational, and neurological processes that may help people avoid tempting relationship alternatives.     

Extra‐powerful on the visuo‐perceptual space,but variable on the number space: Different effects of optokinetic stimulation in neglect patients

We studied the effects of optokinetic stimulation (OKS; leftward, rightward, control) on the visuo‐perceptual and number space, in the same sample, during line bisection and mental number interval bisection tasks. To this end, we tested six patients with right‐hemisphere damage and neglect, six patients with right‐hemisphere damage but without neglect, and six neurologically healthy participants. In patients with neglect, we found a strong effect of leftward OKS on line bisection, but not on mental number interval bisection. We suggest that OKS influences the number space only under specific conditions.     

Influence of age and sex on line bisection: a study of normal performance with implications for visuospatial neglect

Line bisection is an established clinical task used to diagnose visuospatial neglect. To date, few studies have considered the extent to which age and sex as background variables contribute to bisection performance. Both variables affect the neural substrates underlying cognitive processes and hence the behavioural performance of bisection. The purpose of this study was to examine the effects of age and sex on normal bisection performance, using three different line lengths to elucidate the influence of these potential contributing factors. Seventy men and 70 women, divided equally into seven age-cohorts between 14 and 80 years, bisected lines. Results indicated clear age- and sex-related differences both in the magnitude and direction of bisection deviations across the three line lengths. Differences are discussed in terms of neural changes across the adult lifespan including hemispheric differences and hormonally mediated changes.     

What Is Line Bisection in Unilateral Spatial Neglect?: Analysis of Perceptual and Motor Aspects in Line Bisection Tasks

Three patients with unilateral spatial neglect could detect the difference of length between the right and left segments when a line had a transection mark. To examine the effect of response mode, the manual line bisection task and a new “line bisection task by fixation” were given to the patients. In tasks that used lines with no landmark, they showed apparent rightward errors. The results suggest that line bisection is not a task that examines the ability of patients with neglect to compare the right and left extents of a line. Where to fixate as the subjective midpoint may determine the rightward errors of bisection, whether manual response is used or not.