Directional hypokinesia in spatial hemineglect: a case study

Body schema and body image as internal representations of the body, and their disorders. An historical review

Since the early 1900s, the terms body schema and body image denoted the internal representations of the body. Bonnier's (1905, Revue Neurologique, 13, 605) schema is a conscious spatial representation of the size, shape, and position of the body, and of body parts, whose dysfunction brings about aschématia, and hypo-, hyper-, and paraschématia. The two schemata of Head and Holmes (1911, Brain, 34, 102) are an unconscious plastic postural schema, for the maintenance of posture and balance and for the coding of the position of body parts, and a conscious superficial schema, for the localisation of somatosensory stimuli. Pick's (1922, Psychologische Forschung, 1, 303) body schema refers to a structural description of the body, including the position of body parts and their spatial relationships, defective in autotopagnosia. Schilder's (1935, The image and appearance of the human body) body image is a comprehensive construct, covering physiological, evolutional, neurological and neuropsychological, psychiatric and sociological aspects. Lhermitte's (1939, L'image de notre corps) image, based on the views of the abovementioned authors, is defective in bodily neuropsychological disorders. The two terms have been used interchangeably, to denote (hemi-)asomatognosia, anosognosia, autotopagnosia, depersonalisation, personal neglect, phantom and supernumerary limbs, somatoparaphrenia. Their properties have been summarized with general dichotomies: schema for action in space ("where" system), image for perception ("what" system), after primary sensory processing. While schema and image fractionated into multiple representations of aspects of the body, the two terms are still used to refer to some of these representations, and to their disorders.

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.

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.

Exploring the Jastrow Illusion in Humans ( Homo sapiens), Rhesus Monkeys ( Macaca mulatta), and Capuchin Monkeys ( Sapajus apella)

In the Jastrow size illusion, two vertically stacked but offset stimuli of identical size are misperceived such that the bottom stimulus is overestimated relative to the top stimulus due to their spatial layout. In this study, we explored whether nonhuman primates perceive this geometric illusion in the same manner as humans. Human adults, rhesus macaques, and capuchin monkeys were presented with a computerized size discrimination task including Jastrow illusion probe trials. Consistent with previous results, humans perceived the illusory stimuli, validating the current experimental approach. Adults selected the bottom figure as larger in illusion trials with identical shapes, and performance was facilitated in trials with a true size difference when the larger figure was positioned at bottom. Monkeys performed very well in trials with a true size difference including difficult discriminations (5% difference in stimuli size), but they did not show evidence of the Jastrow illusion. They were indifferent between top and bottom stimuli in the illusory arrangement, showing no evidence of a human-like (or reversed) bias. These results are considered in light of differences in perceptual processing across primates and in comparison to previous comparative studies of the Jastrow and other size illusions.

Analysing non-motor bias in unilateral neglect with a new variant of the line bisection task

PRIMARY OBJECTIVE

To develop a new variant of the line-bisection task for assessing non-motor (attentional, representational, etc.) bias in unilateral neglect (UN), i.e. the exactly bisected line selection task (EBLST).

METHODS AND PROCEDURES

Nine patients with UN were included in this study. In the EBLST, multiple horizontal lines, bisected in various proportions, were presented. The participants chose the most equally bisected line and then pointed to the bisector of the chosen line. To avoid the influence of motor bias, the participants used perceptual judgement first. The conventional line-bisection task was also performed. The deviation of the subjective midpoint was measured for each participant in both tasks.

MAIN OUTCOMES AND RESULTS

Eight participants showed obvious rightward deviation in the EBLST, thus resulting in being classified as patients with non-motor neglect. Five participants showed greater deviation in the EBLST than in the line-bisection task.

CONCLUSION

Non-motor function in patients with UN was successfully assessed by the EBLST.

Anatomical correlates of directional hypokinesia in patients with hemispatial neglect

Unilateral spatial neglect (neglect) is a syndrome characterized by perceptual deficits that prevent patients from attending and responding to the side of space and of the body opposite a damaged hemisphere (contralesional side). Neglect also involves motor deficits: patients may be slower to initiate a motor response to targets appearing in the left hemispace, even when using their unaffected arm (directional hypokinesia). Although this impairment is well known, its anatomical correlate has not been established. We tested 52 patients with neglect after right hemisphere stroke, and conducted an anatomical analysis on 29 of them to find the anatomical correlate of directional hypokinesia. We found that patients with directional hypokinesia had a lesion involving the ventral lateral putamen, the claustrum, and the white matter underneath the frontal lobe. Most importantly, none of the patients without directional hypokinesia had a lesion in the same region. The localization of neglect's motor deficits to the basal ganglia establishes interesting homologies with animal data; it also suggests that a relative depletion of dopamine in the nigrostriatal pathway on the same side of the lesion may be an important pathophysiological mechanism potentially amenable to intervention.

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.

Categorisation of 'perceptual' and 'premotor' neglect patients across different tasks: is there strong evidence for a dichotomy?

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 is consistent across different line bisection assessment techniques that have, in the past, been designed to tease these potentially overlapping aspects of hemispatial neglect apart. Twelve patients with hemispatial neglect and three control groups were tested with the Overhead Task, adapted from Nico [Neuropsychologia 34 (1996) 471] in which patients were asked to bisect lines that were mirror reversed, the Pulley Device Technique, adapted from Bisiach et al. [Neurology 40 (1990) 1278] in which they had to perform a movement opposite to the direction of the transaction mark that bisected the line and the Landmark Test, adapted from Milner et al. [Neuropsychologia 30 (1992) 515] in which they had to manually point to the half of a centrally pre-bisected line that, to them, appeared shorter. The specific question was whether these three tasks 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 three techniques. Just 1 out of the 12 patients, was consistently classified across all three tasks. It seemed that despite the fact that all tasks essentially required a line bisection response, the perceptual and motor differences between the tasks were still great enough to result in inconsistent classifications. The Landmark Task classified the majority of patients into the perceptual neglect category, while the Overhead and Pulley Device Techniques tended to identify more patients as suffering from a premotor deficit (albeit not the same set of patients).

The traffic light paradigm: a reaction time task to study laterally directed arm movements

Patients with unilateral brain damage may show slowed or hypometric arm movements toward the contralesional space, as compared to movements directed towards the side of the brain lesion. The present article describes a reaction time paradigm devised to study accuracy and latency of directional arm movements in normal human subjects and brain-damaged patients. Experimental paradigms hitherto used to explore directional motor disorders often do not reliably disentangle between perceptual and motor factors, because they employ lateralized perceptual stimuli. The traffic light paradigm, instead, consists of visual stimuli presented on the vertical midline (like a traffic light) and hand responses to be produced in either hemispace. Thus, participants have to produce lateralized arm responses to central visual stimuli. Performance on this 'motor' paradigm can be contrasted with performance on a 'perceptual' reaction time task, consisting of similar, but lateralized visual stimuli and central motor responses. Results obtained with these paradigms on normal participants and brain-damaged patients are presented and discussed. These results give empirical support to the claim that the traffic light paradigm is suitable to study directional motor disorders in relative isolation from perceptual biases.

Extrapersonal visual unilateral spatial neglect and its neuroanatomy

The neural correlates of left extrapersonal visual unilateral spatial neglect (VUSN), the more extensively investigated component of the neglect syndrome, are reviewed. Damage to a number of right-hemisphere regions brings about VUSN: the posterior parietal cortex (inferior parietal lobule) and, although less frequently, the premotor cortex and subcortical structures, such as the thalamus and the basal ganglia, and white matter fiber tracts. In recent years, a number of studies have investigated the possible association of specific components of left VUSN with damage to specific brain regions within the right hemisphere. The putative distinction most extensively investigated from an anatomical perspective concerns the perceptual vs premotor components of VUSN. In addition, a fine-grain componential analysis of the behavioral tasks used to investigate VUSN is providing more specific insight into the pathological mechanisms underlying the variety of its manifestations. The emerging pattern is that USN is a multifarious disorder, in which specific deficits are associated with damage localized in discrete brain regions and neural circuits. These data concur with evidence from other domains (functional neuroimaging, neurophysiology) to suggest a highly multicomponential neural and functional architecture of spatial cognition.

Neglect without extinction

A patient, AB, is reported who showed clear signs of neglect but no extinction (N+ E-). Several hypotheses proposed to account for this dissociation were put to the test. The postulated association between motor neglect and extinction did not hold good, nor did the possibility that the N+ E- dissociation may be traced back to the difference in test requirements and therefore observed only in patients with object-centred neglect. Likewise, manipulating the physical features of the stimuli (relative size, exposure time, presentation synchrony) did not elicit extinction. However, when the task demands were modified by asking the patient to perform a further spatial analysis of the stimuli, rather than simply detect them, extinction emerged. Since AB performed well on several neglect tasks requiring parallel processing, while failing all tasks calling for serial processing, the hypothesis is put forward that AB's N+ E- dissociation could be interpreted within the parallel/serial distinction framework.

Dopaminergic stimulation in unilateral neglect

OBJECTIVE

To explore the hypothesis that dopaminergic circuits play a part in the premotor components of the unilateral neglect syndrome, the effects of acute dopaminergic stimulation in patients with neglect were studied.

METHODS

Two tasks were evaluated before and after subcutaneous administration of apomorphine and placebo: a circle crossing test and a test of target exploration (a modified version of the bell test), performed both in perceptual (counting) and in perceptual-motor (pointing) conditions.

SUBJECTS

Four patients with left neglect.

RESULTS

After dopaminergic stimulation, a significant improvement was found compared with placebo administration and baseline evaluation, in the performance of the two tests. Three of the patients had a more marked improvement in the perceptual-motor condition (pointing) of the task than the perceptual condition (counting).

CONCLUSIONS

The findings suggest that dopaminergic neuronal networks may mediate, in different ways, both perceptive and premotor components of the unilateral neglect syndrome.

Visuomotor processing in unilateral neglect

The extent to which visual information on the contralateral, unattended side influences the performance of patients with hemispatial neglect was studied in a visuomotor reaching task. We replicated the well-established finding that, relative to target-alone trials, normal subjects are slower to reach to targets in the presence of visual distractors which appear either ipsilateral or contralateral to the target, with greater interference in the former condition. Six patients with hemispatial neglect showed even greater interference than did the normal subjects when the distractor appeared ipsilaterally but showed no significant interference from contralateral distractors. This pattern of performance was qualitatively similar for patients with lesions restricted to posterior regions and for patients with more extensive lesions involving both posterior and anterior brain regions. These findings suggest that, in the visuomotor domain, information on the contralateral side is processed minimally, if at all, in patients with hemispatial neglect.

Perception and action in hemispatial neglect

Hemispatial neglect is a neurological disorder which entails a spatial bias that penalizes events occurring in the hemispace contralateral to a brain lesion. Mechanisms operating upon various stages ranging from perception to action have been invoked to explain neglect. The present study explores the contribution of a defective programming of arm movements towards the neglected hemispace to neglect behaviour. Two reaction time tasks -- a "perceptual" task and a "motor" task -- were performed by right brain-damaged (RBD) patients with left hemispatial neglect, RBD patients without signs of neglect and control subjects. The perceptual task consisted of lateralized visual stimuli and central motor responses, whereas the motor task consisted of visual stimuli presented on the vertical midline and hand responses to be produced in either hemispace. Neglect patients showed a rightward bias on the perceptual task, but only two RBD patients (showing no signs of severe neglect) were consistently slowed in producing leftward motor responses. Different reference frames may thus be used in perceptual tasks and tasks involving arm movements. We conclude that hemispatial neglect commonly results from attentional impairments operating upon a visual perceptual frame of reference; additional deficits appear to be necessary to produce a directional motor disorder.

Visual neglect associated with frontal lobe infarction

Five patients with left-sided visual neglect following focal infarction of the right frontal lobe are presented. Lesion location was assessed using computed tomography or magnetic resonance imaging. The common area of lesion overlap was small, being confined to the dorsal aspect of the inferior frontal gyrus (Brodmann's area 44) and the immediate underlying white matter. This cortical region is part of the homologue of Broca's area in the right hemisphere and is considered to be part of human premotor cortex. The association of neglect with injury to this area suggests it may play an important role in directing attention in visual space.

Frontal lobe mechanisms subserving vision-for-action versus vision-for-perception

In the typical course of daily events, we often gaze at an object, attend to its features and its place, reach toward it and grasp it, all with an awareness of what we are doing at the time. But behavior is not always thus. Gaze, attention, limb movement direction and awareness can be behaviorally dissociated from each other, and this review focuses on one such dissociation: that between the perception of an object and the use of that object's inherent spatial and nonspatial information for mediating visuomotor control. We review evidence that partially different neuronal systems underlie these two aspects of visual information processing. In neurophysiological studies of the primate frontal lobe, it has been possible to demonstrate that neural signals appearing to be visual responses reflect, at least in part, the motor significance of a stimulus. This finding has been confirmed, in separate studies, for both spatial and nonspatial visual information and supports the hypothesis that some frontal cortex activity reflects the selection and guidance of action rather than the properties of visual stimuli, per se. These findings are discussed in the context of neuropsychological studies indicating that accurate and appropriate movements are possible without perceptual awareness of the information guiding those movements.

Differential effects of line length on bisection judgements in hemispatial neglect

Recent studies have shown that certain symptoms of spatial neglect are co-determined by two major factors: one whose general nature is perceptual, the other whose nature is directional and/or motor. In the present study, patients whose neglect was classified as predominantly 'perceptual' or 'directional' through use of the Landmark task (Milner, Brechmann and Pagliarini, 1992) were asked to bisect lines ranging in length from 20 to only 2.5 cm. It was found that the one patient with predominantly directional neglect showed large rightward errors at all line lengths. In contrast, those with perceptual neglect made very small (usually leftward) errors on short lines. It is argued that it is essential to separate these different subtypes of neglect patient if we are to understand the causation of their behaviour in tasks such as line bisection.

Spatial attention in the mental architecture: evidence from neuropsychology

Using neuropsychological evidence, this paper examines whether spatial attention functions as a domain-specific module or as a more general-purpose central processor. Data are presented from two spatial attention cuing tasks completed by subjects, with an acquired attentional deficit, and control subjects. In both tasks, an arrow indicated with high probability the side of response (response task) or the side of space on which the stimulus would appear (visuospatial task). In the response task, the stimuli appeared foveally and the response component was lateralized, and in the visuospatial task, the stimuli were lateralized and the response component remained constant in the midline. Only the neglect subjects showed a disproportionate increase in reaction time on both the response and visuospatial tasks when the arrow cued the subject to the ipsilateral side and the stimulus or response was on the side of space contralateral to the lesion. The substantial association across the two tasks suggests that a common underlying internal spatial representation subserves perception and action. While this finding is consistent with Fodor's view of a cross-domain processor, it does not meet all of his criteria of a central processor. We conclude, therefore, that the posterior attentional mechanism is strictly neither a module nor a central processor. Rather, these results suggest that a common attentional mechanism may subserve behavior in domains that are tightly coupled.

Seeing the forest but only half the trees?

In visuo-spatial neglect after right hemisphere damage, patients fail overtly to notice and respond to stimuli on the side of space contralateral to lesion. Nonetheless, these neglected stimuli may covertly influence their performance in other tasks less direct than overt detection or identification. We report here a new type of dissociation between two forms of conscious perceptual awareness in a patient with left neglect. J.R. was shown hierarchical drawings in which a larger (global) form, such as a geometric figure or an alphabetic letter, is composed of smaller (local) forms (dots, circles, or letters). She gave accurate verbal reports of the global structure of these stimuli (Navon figures), yet when required to cross out the smaller subfigures, she only cancelled those on the right of each global figure. Conscious perception of the whole does not automatically lead to visual awareness of all the parts thereof.

The effect of space location on neglect depends on the nature of the task

It has been often reported that in patients with visual neglect line bisection is more accurate in the right than in the left hemispace. However, no data are available on the effect of hemispace on reading errors associated with neglect. We examined a 62-year-old man who presented with severe left neglect following a large infarction in the right cerebral hemisphere. The patient was asked to read 180 words aloud and to bisect 90 lines. Stimuli were presented in three different spatial locations: across the centre, to the right or to the left of the body midline. Line bisection was significantly more accurate in the right hemispace compared with the centre, or the left hemispace. In contrast, reading was significantly more accurate with words presented on the left side than on the centre or right side. This is the first time that such dissociation has been reported. We hypothesize that the dissociation depends on the nature of the stimuli and on the different cognitive demands of the tasks.

Preserved leftward movement in left unilateral spatial neglect due to frontal lesions

Three patients with left unilateral spatial neglect after predominantly frontal lobe lesions were asked to extend a horizontal line leftwards to double its original length. In this line extension task, they readily executed movements in or towards the contralesional left space. They performed the task in the left and right hemispaces as well as in the midline. The mean extension lengths did not differ significantly among these three spatial conditions. These results suggest that directional hypokinesia takes little part in left unilateral spatial neglect due to frontal lobe lesions. It is considered that the patients could execute leftward movements as the task oriented their attention sufficiently to the left. Two of the three patients, like reported cases with frontal neglect, showed a typical exploratory deficit for the left space in the line cancellation test. Such a deficit found in the traditional tasks, however, does not mean the presence of directional hypokinesia. All three patients showed visual extinction on double simultaneous stimulation. An attentional mechanism seems to play a predominant part in unilateral spatial neglect due to frontal lesions.

Homing in on neglect: a case study of visual search

We report three studies of visual search in a patient with left neglect after a right parietal infarct. Manipulations whereby the patient's attention is explicitly drawn to the spatial extent of the page on which the stimuli for cancellation are displayed have little or no effect on the number of targets cancelled. The results are consistent with a "zoom lens" model of attentional deployment. "Neglect" on search tasks seems to reflect a systematic bias that emerges when global attention is constricted to permit analysis of local features.