Horizontal space misrepresentation in unilateral brain damage. II. Eye-head centered modulation of visual misrepresentation in hemianopia without neglect

A Meta-Analysis of Line Bisection and Landmark Task Performance in Older Adults

Young adults exhibit a small asymmetry of visuospatial attention that favours the left side of space relative to the right (pseudoneglect). However, it remains unclear whether this leftward bias is maintained, eliminated or shifted rightward in older age. Here we present two meta-analyses that aimed to identify whether adults aged ≥50 years old display a group-level spatial attention bias, as indexed by the line bisection and the landmark tasks. A total of 69 datasets from 65 studies, involving 1654 participants, were analysed. In the meta-analysis of the line bisection task (n = 63), no bias was identified for studies where the mean age was ≥50, but there was a clear leftward bias in a subset where all individual participants were aged ≥50. There was no moderating effect of the participant’s age or sex, line length, line position, nor the presence of left or right cues. There was a small publication bias in favour of reporting rightward biases. Of note, biases were slightly more leftward in studies where participants had been recruited as part of a stand-alone older group, compared to studies where participants were recruited as controls for a clinical study. Similarly, no spatial bias was observed in the meta-analysis of the landmark task, although the number of studies included was small (n = 6). Overall, these results indicate that over 50s maintain a group-level leftward bias on the line bisection task, but more studies are needed to determine whether this bias can be modulated by stimulus- or state-dependent factors.

Spontaneous ocular positioning during visual imagery in patients with hemianopia and/or hemineglect

Spontaneous eye movements during imagery are not random and can be used to study and reveal mental visualization processes (Fourtassi et al., 2013; Johansson et al. 2006). For example, we previously showed that during memory recall of French towns via imagery healthy individuals looks straight ahead when recalling Paris and their subsequent gaze positions are significantly correlated with the real GPS coordinates of the recalled towns. This correlation suggests that memory retrieval is done via depictive representations as it is never found when the towns are recalled using verbal fluency. In the present paper we added to this finding by showing that the mental image is spontaneously centered on the head or body midline. In order to investigate the capacities of visual imagery in patients, and by extension, the role of primary visual cortex and fronto-parietal cortex in spatial visual imagery, we recorded gaze positions during memory recall of French towns in an imagery task, a non-imagery task (verbal fluency), and a visually-guided task in five patients with left or right hemianopia and in four patients with hemineglect (two with left hemianopia and two without). The correlation between gaze position and real GPS coordinates of the recalled towns was significant in all hemianopic patients, but in patients with hemineglect this was only the case for towns located on the right half of the map of France. This suggests hemianopic patients can perform spatially consistent mental imagery despite direct or indirect unilateral lesions of the primary visual cortex. In contrast, the left-sided towns recalled by hemineglect patients, revealed that they have some spatial inconsistency or representational difficulty. Hemianopic patients positioned and maintained their gaze in their contralesional hemispace, suggesting that their mental map was not centered on their head or body midline. This contralesional gaze positioning appeared to be a general compensation strategy and was not observed in patients with neglect (with or without hemianopia). Instead, neglect patients positioned their gaze in their ipsilesional hemispace and only when performing the visual imagery task. These findings are discussed in the context of the role of occipital and fronto-parietal cortices in the neuroanatomical model of visual imagery developed by Kosslyn et al. (2006).

Bisecting or not bisecting: this is the neglect question. Line bisection performance in the diagnosis of neglect in right brain-damaged patients

In the present study we analysed the bisecting behaviour of 287 chronic right brain-damaged patients by taking into account the presence and severity of extrapersonal and/or personal neglect diagnosed with the hemineglect battery. We also analysed right brain-damaged patients who had (or did not have) neglect according to their line bisection performance. Our results showed that performance of the line bisection task correlates with performance of cancellation tasks, reading and perceptual tasks, but not with the presence of personal neglect. Personal neglect seems to be unrelated to line bisection behaviour. Indeed, patients affected by extrapersonal and personal neglect do not show more severe neglect in line bisection than patients with only extrapersonal neglect. Furthermore, we observed that 20.56% of the patients were considered affected or not by neglect on the line bisection task compared with the other spatial tasks of the hemineglect battery. We conclude that using a battery with multiple tests is the only way to guarantee a reliable diagnosis and effectively plan for rehabilitative training.

Human infants' preference for left-to-right oriented increasing numerical sequences

While associations between number and space, in the form of a spatially oriented numerical representation, have been extensively reported in human adults, the origins of this phenomenon are still poorly understood. The commonly accepted view is that this number-space association is a product of human invention, with accounts proposing that culture, symbolic knowledge, and mathematics education are at the roots of this phenomenon. Here we show that preverbal infants aged 7 months, who lack symbolic knowledge and mathematics education, show a preference for increasing magnitude displayed in a left-to-right spatial orientation. Infants habituated to left-to-right oriented increasing or decreasing numerical sequences showed an overall higher looking time to new left-to-right oriented increasing numerical sequences at test (Experiment 1). This pattern did not hold when infants were presented with the same ordinal numerical information displayed from right to left (Experiment 2). The different pattern of results was congruent with the presence of a malleable, context-dependent baseline preference for increasing, left-to-right oriented, numerosities (Experiment 3). These findings are suggestive of an early predisposition in humans to link numerical order with a left-to-right spatial orientation, which precedes the acquisition of symbolic abilities, mathematics education, and the acquisition of reading and writing skills.

Spontaneous recovery and treatment effects in patients with homonymous visual field defects: a meta-analysis of existing literature in terms of the ICF framework

Homonymous visual field defects (HVFDs) are a common consequence of posterior brain injury. Most patients do not recover spontaneously and require rehabiliation. To determine whether a certain intervention may help an individual patient, it is necessary to predict the patient's level of functioning and the effect of specific training. We provide an overview of both the existing literature on HVFDs in terms of the International Classification of Functioning, Disability, and Health (ICF) components and the variables predicting the functioning of HVFD patients or the effect of treatment. We systematically analyzed 221 publications on HVFD. All variables included in these articles were classified according to the ICF, as developed by the World Health Organization, and checked for their predictive value. We found that ICF helps to clarify the scope of the existing literature and provides a framework for designing future studies, which should consider including more outcome measures related to Activities and Participation. Although several factors have been described that predict HVFD patients' level of functioning or the effects of training, additional research is necessary to identify more.

Exploring near and far regions of space: distance-specific visuospatial neglect after stroke

Visuospatial neglect has been observed in the horizontal (left/right) and vertical (up/down) dimension and depends on the distance at which a task is presented (near/far). Previously, studies have mainly focused on investigating the overall severity of neglect in near and far space in a group of neglect patients instead of examining subgroups of neglect patients with different types of distance-specific neglect. We investigated the spatial specificity (near vs. far space), frequency, and severity of neglect in the horizontal and vertical dimensions in a large group of stroke patients. We used three tasks to assess neglect in near (30 cm) and far (120 cm) space: a shape cancellation, letter cancellation, and a line bisection task. Patients were divided into four groups based on their performance: a group without neglect (N-F-), a near only neglect (N+F-), a far only neglect (N-F+), and a near and far neglect group (N+F+). About 40% of our sample showed neglect. Depending on the task, N+F- was observed in 8 to 22% of the sample, whereas N-F+ varied between 8% and 11%, and N+F+ varied between 11% to 14% of the sample. The current findings indicate that horizontal and vertical biases in performance can be confined to one region of space and are task dependent. We recommend testing for far space neglect during neuropsychological assessments in clinical practice, because this cannot be diagnosed using standard paper-and-pencil tasks.

Non-lateralised deficits in anti-saccade performance in patients with hemispatial neglect

We tested patients suffering from hemispatial neglect on the anti-saccade paradigm to assess voluntary control of saccades. In this task participants are required to saccade away from an abrupt onset target. As has been previously reported, in the pro-saccade condition neglect patients showed increased latencies towards targets presented on the left and their accuracy was reduced as a result of greater undershoot. To our surprise though, in the anti-saccade condition, we found strong bilateral effects: the neglect patients produced large numbers of erroneous pro-saccades to both left and right stimuli. This deficit in voluntary control was present even in patients whose lesions spared the frontal lobes. These results suggest that the voluntary control of action is supported by an integrated network of cortical regions, including more posterior areas. Damage to one or more components within this network may result in impaired voluntary control.

Monocular patching may induce ipsilateral "where" spatial bias

Spatial bias is an asymmetry of perception and/or representation of spatial information - "where" bias -, or of spatially directed actions - "aiming" bias. A monocular patch may induce contralateral "where" spatial bias (the Sprague effect [Sprague, J. M. (1966). Interaction of cortex and superior colliculus in mediation of visually guided behavior in cat. Science, 153(3743), 1544-1547]). However, an ipsilateral patch-induced spatial bias may be observed if visual occlusion results in top-down, compensatory re-allocation of spatial perceptual or representational resources toward the region of visual deprivation. Tactile distraction from a monocular patch may also contribute to an ipsilateral bias. To examine these hypotheses, neurologically normal adults bisected horizontal lines at baseline without a patch, while wearing a monocular patch, and while wearing tactile-only and visual-only monocular occlusion. We fractionated "where" and "aiming" spatial bias components using a video apparatus to reverse visual feedback for half of the test trials. The results support monocular patch-induced ipsilateral "where" spatial errors, which are not consistent with the Sprague effect. Further, the present findings suggested that the induced ipsilateral bias may be primarily induced by visual deprivation, consistent with compensatory "where" resource re-allocation.

Gaze but not arrows: a dissociative impairment after right superior temporal gyrus damage

Superior temporal sulcus (STS) activation has consistently been demonstrated in the normal brain when viewing eyes, and thus this area is implicated as a gaze processing region in humans. In a recent report, we have presented a case, M.J., with a well-circumscribed lesion to the right superior temporal gyrus (STG), who demonstrated impaired discrimination of gaze direction. In the aim to make distinct whether this impairment is unique to gaze, we have applied a spatial cueing paradigm established by Kingstone and colleagues. In our experiment, pictorial gaze and symmetrical arrows were centrally presented as non-predictive, spatial cues in detecting peripheral targets. Fifteen normal subjects and M.J. participated in the experiment. In concordance with previous reports, controls demonstrated a significant facilitation of reaction times in detecting targets cued by congruent gaze/arrows, compared with incongruent cues. In striking contrast, M.J. showed no such congruency advantage for gaze, in the face of a normal congruency advantage for arrows. We have demonstrated that a circumscribed lesion to the right STG impairs the ability to utilize biological directional information such as gaze, but leaves the non-biological counterpart (arrows) intact. This dissociation implies that indeed, the STS specializes in processing gaze.

A deficit in discriminating gaze direction in a case with right superior temporal gyrus lesion

The superior temporal sulcus (STS) region is well recognized as being heavily involved in detecting and discriminating gaze. Lesions confined to this area are quite rare in humans, and so the research has mainly depended on animal studies and functional neuroimaging in normal human subjects. We report one such rare case, a 54-year-old Japanese female with a possible congenital s anomaly who, after a cerebral hemorrhage, demonstrated a lesion almost completely confined to the entire right superior temporal gyrus (STG). In the subacute phase, the patient showed evidence of left hemispatial neglect, from which she gradually recovered. In the chronic phase, she showed a puzzling difficulty in obtaining eye-contact. We have conducted, in conjunction with conventional neuropsychological evaluations, experimental assessment of her ability in gaze cognition. Her performance on neuropsychological testing demonstrated no compromise in intellect, memory, or language skills, and a close-to-full recovery from neglect. On gaze cognition experiments, she was repeatedly shown to perceive left gaze as straight, and to a lesser degree, straight gaze as right. We suggest that the function of the STG in detecting gaze, together with the directional information it receives from earlier visual areas, may be associated, when damaged, with this deficit in detecting contra-directional gaze. We have demonstrated for the first time that a single circumscribed lesion to the STG results in both gaze processing deficit and concurrent aberrant gaze behavior of the victim herself, implicating a mechanism within the STG as an interface between gaze of others and gaze of self.

Causes of cross-over in unilateral neglect: between-group comparisons, within-patient dissociations and eye movements

Patients with left unilateral neglect bisect long horizontal lines to the right of the true centre. However, when given short lines, many of the same patients mark the midpoint to the left of the true centre, towards the otherwise neglected space. This paradoxical phenomenon has been termed 'cross-over' and is difficult to explain based on current accounts of the neglect syndrome. To explore the causes of cross-over, in a first study we evaluated bisection of 20, 100 and 200 mm horizontal lines in groups of unilateral brain-damaged patients with neglect and hemianopia, with neglect and no hemianopia, with hemianopia and no neglect and without neglect or hemianopia. Cross-over of 20 mm lines was found only in neglect patients with hemianopia. To ascertain further the influence of visual field defects on cross-over, in a second study we compared the performance of two right-brain-damaged patients with contralesional neglect and inferior quadrantanopia with that of a patient with inferior quadrantanopia and no neglect. Patients bisected lines oriented so as to cross or uncross the blind quadrant of the visual field. When short 20 mm lines crossed the blind quadrant, neglect patients showed cross-over; when the same lines crossed the seeing quadrants cross-over was absent. These findings were confirmed by the examination of a neglect patient with sparing of the central 5 degrees of the contralesional left visual hemifield in the right eye and no sparing in the left eye. In monocular viewing, cross-over was present when 20 mm lines were bisected with the left eye and absent when bisected with the right eye. Recording of eye movements showed that at the moment of bisection left eye fixations shifted towards the contralesional line endpoint whereas right eye fixations remained anchored to the centre of the line. With long lines, both eyes deviated ipsilesionally. These results show that in neglect patients ipsilesional deviation in the bisection of long lines turns into apparently paradoxical contralesional bisection of short ones only when these cross a retinotopically blind sector of the neglected space. Cross-over seems to depend on the small spatial effects produced by reflexive contralesional gaze shifts allowing eccentric fixations with the seeing hemifield. During the bisection of long lines, these effects are cancelled out by the strong attentional deviation induced by the marked extension of the ipsilesional line segment. This explanation establishes coherence between cross-over and current accounts of the neglect syndrome.

Misprojection of landmarks onto the spatial map

It has been suggested that neglect patients misrepresent the metric spatial relations along the horizontal axis (anisometry). The "fabric" of their internal spatial medium would be distorted in such a way that physically equal distances appear relatively shorter on the contralesional side (canonical anisometry). The case of GL, a 76-year-old lady with left neglect on visual search tasks, is presented. GL showed severe relative overestimation on the left (contralesional) side on two independent tasks evaluating the metrics of her internal representation. A qualitatively similar pattern was found in two out of 10 other neglect patients who performed the second task. This behavior cannot be accounted for by the canonical anisometry hypothesis. Nevertheless, GL produced a relative left overextension (underestimation) when trying to set the endpoints of a virtual line given its midpoint (Endpoints Task). An interpretation of these results is offered in terms of a misprojection of relevant landmarks onto the internal representation without assuming distortion of its "fabric."

Underestimation of contralateral space in neglect: a deficit in the “where” task

Space perception was investigated in right brain damaged patients with ( N=13) and without neglect ( N=5; control group). Patients were requested to localise a target tachistoscopically flashed at various eccentricities along the horizontal meridian. All patients had an intact visual field and spared ability to manually point to a target. To segregate magno- and parvo-pathway activity, stimuli modulated in either luminance or chromatic contrast were used. Patients were required to verbally report the stimulus position (verbal task) or to manually point to the stimulus (pointing task). Neglect patients reported the stimuli in the left visual field closer to the centre than they actually were. In the verbal test, underestimation was about 7 deg at the most eccentric position tested (20 deg), and decreased linearly for smaller eccentricities. The effect was similar but less marked in the pointing task. No difference was found for stimuli with luminance or chromatic contrast. Space underestimation was confined to the contralesional space; no evidence of misperception was detected in the ipsilesional hemifield. The present findings are consistent with the view that contralesional space representation is compressed in neglect patients.

The anatomy of neglect without hemianopia: a key role for parietal-frontal disconnection?

We investigated the anatomical correlates of chronic unilateral neglect in right brain damaged patients with no visual field defects. Independently from basal ganglia or thalamus involvement, neglect patients had a subcortical area of maximal lesion overlap (maxov) in the superior longitudinal fasciculus (SLF). Neglect patients without lesion of subcortical nuclei had an additional maxov area in the rostralmost limit of the supramarginal gyrus (SmG). Patients without neglect showed a maxov area in the corticospinal tract with no involvement of the SLF or SmG. These findings call attention to the role of parietal-frontal disconnection in the pathogenesis of neglect. This disconnection can make neglect generalised and enduring also in patients suffering only partial damage of the parietal-temporal cortex, and who would otherwise show more selective attentional impairments.

Comparison of the Milner and Bisiach Landmark Tasks: can Neglect Patients be Classified Consistently?

The aim of the presented studies was to investigate whether classifications of neglect patients into perceptual (i.e. identifying a patient as suffering from mainly attentional/space representation deficits) and premotor (judging the main impairment to be related towards actions into contralesional space) categories are consistent across similar Landmark techniques that have, in the past, been designed to tease these potentially overlapping aspects of hemispatial neglect apart. Thirteen patients with hemispatial neglect were tested both with the Landmark Test, adapted from Milner et al. (1992; 1993) in which they had to manually point to the half of a centrally pre-bisected line that, to them, appeared shorter and the motor version of the Bisiach Landmark Test (Bisiach et al., 1998) in which, rather than just judging a centrally prebisected line, they had to judge asymmetrically bisected lines as well. The specific question was whether these two tasks, which are very similar, would categorise the same set of patients in the same way. Most patients could be classified into either the premotor or perceptual category in each task, but no consistent categorisation emerged across the two tests. Just three out of the thirteen patients were consistently classified across both tests. Despite the apparent similarity of the two tests the Milner Landmark Test proved to be much more sensitive to identifying even a slight perceptual bias and seems therefore the test of choice if identification of perceptual bias is the major interest.

Line bisection following hemispherectomy

Two left- and right-hemispherectomized patients with contralateral hemianopia and 20 normal controls were administered a line bisection task. All hemispherectomized patients showed a strong bisection bias towards their blind visual field. This contralateral bias persisted when patients were forced to start scanning within their blind hemifield, supporting the idea of a strategic adaptation of attention towards the blind visual field. In all patients the hemispherectomy was performed as a result of cortical abnormality (congenital or acquired) and therefore early changes in functional cerebral organization may have occurred in these patients. The absence of a neglect-like ipsilateral bias and the presence of a hemianopic-like contralateral bias in line may represent a functional deficit or suggest that plastic changes following hemispherectomy induced an adaptive functional re-organization of spatial attention in both left- and right-hemispherectomized patients.

Eye-movement patterns do not mediate size distortion effects in hemispatial neglect: looking without seeing

Over the last decade a range of studies have shown that some patients with hemispatial neglect subjectively underestimate the size of objects presented in their contralesional hemispace. Recently, it has been suggested that the effect is simply due to either hemianopia [Brain 124 (2001) 527], or the combination of neglect and hemianopia [Neurology 52 (1999) 1845]. In the current study we asked right hemisphere lesioned patients with and without neglect and hemianopia as well as healthy controls to judge either two horizontal or vertical lines presented simultaneously in right and left hemispace and monitored their eye movements. Three out of the six patients showed the predicted size distortion effect for horizontal lines. We found no evidence that the effect was mediated by eye movements. The two neglect patients who showed the strongest left side underestimation showed symmetrical (left, right) scanning of the lines both in terms of number of fixations and fixation time, yet they still failed to judge the relative size veridically. In addition, we did not find strong evidence for a link with hemianopia. We therefore propose that the effect reflects a computational/representational failure of processing for horizontal extent.

Horizontal space misrepresentation in unilateral brain damage. I. Visual and proprioceptive-motor influences in left unilateral neglect

Patients with unilateral neglect can misperceive horizontal distances in the contralesional space as being shorter than equivalent ipsilesional ones. We evaluated the visual and motor-proprioceptive components of space misrepresentation through a distance reproduction task performed both with and without visual guidance. Four groups of right brain damaged patients (neglect with hemianopia (N+H+), neglect with inferior quandrantanopia (N+Q+), neglect without hemianopia (N+H-) and patients without neglect or hemianopia (N-H-)) and one group of healthy controls (C) performed the line bisection task and reproduced horizontal distances either by setting the endpoints or by doubling the length of a line in the contralesional or ipsilesional space. The doubling length task was administered in three different conditions: (a) visuomotor (the patient draws the line in free vision); (b) visual (by sight the patient guides the examiner drawing the line); (c) proprioceptive-motor (the patient is blindfolded and manually inspects and extends the horizontal distance subtended by the line). Compared to C and N-H- patients, only N+H+ patients exhibited a significant ipsilesional shift in line bisection. N+H+ patients showed the most severe contralesional-overextension/ipsilesional-underextension asymmetry in the endpoint, visuomotor and visual line extension task. In the proprioceptive-motor condition no asymmetry was found and N+H- showed greater overextension on both sides of space. In N+H-, brain damage was mainly centered in central-frontal cortex and basal ganglia. These findings re-emphasize the relevance of damage to visual retinotopically organized representations of space in the genesis of horizontal space misrepresentation of neglect patients and suggest the possible association of a non-lateralized defective processing of proprioceptive-motor information with unilateral neglect.