Acceleration perception and spatial distortion in a left unilateral neglect patient

To explain relative leftward overextension in a line extension task by left unilateral neglect subjects, Bisiach et al. (1998) suggested that the representation of space is distorted--i.e., dilated towards the left side. If perception of the velocity of a moving stimulus is due to a calculation of the distance covered per unit time in representational space, then a stimulus with uniform linear motion should be perceived as decelerating when moving leftwards in the visual field of a subject with left unilateral neglect. We investigated the perception of acceleration in a patient with left unilateral neglect and spatial distortion (revealed as relative left overextension in a line extension task) using a task in which the stimuli were right and left moving targets with variable acceleration. The patient's ability to perceive acceleration was much lower (higher acceleration threshold) for leftward movements than rightward movements. Fourteen months later unilateral neglect had improved, and the relative left overextension and decreasing acceleration threshold for leftward movements were reduced. By contrast, alterations in the perception of acceleration for leftward movements were not found in a patient with left unilateral neglect and left underextension and in a patient with right brain damage and left hemianopia. These findings in one patient with left spatial unilateral neglect and a relative left overextension in a line extension task are consistent with the hypothesis that representational space is distorted, with a disproportionate leftward expansion, that affects perception of movement.     

Motor and perceptual factors in pseudoneglect.

An important variant of the traditional line bisection task has involved a mechanical device invented by Bisiach and his colleagues (Bisiach et al. Perceptual and premotor factors of unilateral neglect. Neurology 1990;40:1278-81 [3]). This tool was devised to dissociate motor from perceptual factors in hemi-spatial neglect, by means of a mid-line indicator which moved 'congruently' or 'non-congruently' with the direction of hand movement. In the non-congruent condition, Bisiach was able to demonstrate a reduction, or reversal, of the direction of bisection error in a number of patients with neglect. These errors were interpreted as instances of 'motor' neglect. Bisiach et al. [3] also tested 10 normal subjects, who did not differ on the two conditions of the task. However, the original experiment [3] required the use of the right hand only, and it has since become clear that bisection errors in normal subjects (i.e. pseudoneglect) are more substantial when dextral subjects use their left hands. By using a modified version of the Bisiach Tool we show that there is an effect of the motor versus perceptual condition on this task, but only when subjects use their non-dominant (left) hand.     

Perceptual and premotor neglect: is there an ideal task to categorise patients?

This review focuses on Edoardo Bisiach's particular input into the perceptual/premotor taxonomy within the neglect syndrome and assesses arguments and experimental designs that have been presented both for and against the dichotomy. Bisiach made most crucial contributions to this topic as well as increasing insights into the syndrome of hemispatial neglect more generally. Most importantly, he elucidated its relevance to visual neuropsychological and neuroscientific research.     

Cognition in dyschiria: Edoardo Bisiach's theory of spatial disorders and consciousness

An overview of Bisiach's theory of mental representations and consciousness is presented. Neuropsychological observations on space disorders led Bisiach to consider analogical representations (and not only symbolic representations) as truly 'cognitive', insofar as they are necessary for the normal functioning of linguistic processes. Bisiach's approach to the scientific study of consciousness, conceived both as the private aspect of phenomenal experience and as a monitoring process, is also discussed.     

A study of right unilateral spatial neglect in left hemispheric lesions: the difference between right-handed and non-right-handed post-stroke patients

We report 20 cases of right unilateral spatial neglect caused by lesions in the left cerebral hemisphere. Differences in neuropsychological symptoms and lesions sites are discussed in connection with handedness. Of the right-handed patients, 6 had severe aphasia, 4 had Gerstmann's syndrome, and 1 had pure agraphia, but unilateral spatial neglect in these cases disappeared after a number of months. Six of the non-right-handed patients had moderate-to-severe aphasia, while the other 3 cases had no aphasia at all. Eight of the 9 cases in this group continued to have right unilateral spatial neglect for more than 6 months. Lesion site as determined by CT differed as to hemisphere, but all fell into the common area previously mentioned in connection with such disorders: i.e., the temporal, parietal and occipital lobes.     

Diverse patterns of performance in copying and severity of unilateral spatial neglect

We analysed the performances of 69 patients with left unilateral spatial neglect in copying a multi-object figure, as well as their performance of the line cancellation and line bisection tests. Three patterns of copying were mainly observed. The first pattern was almost satisfactory performance in copying the central figure with occasional omission of the elements located more laterally to the left. The second pattern was omission of the left half of the whole figure, which was the pattern expected of patients with typical left unilateral spatial neglect. The third pattern was left unilateral spatial neglect when copying the central figure, with favourable copying of left lateral objects; this may be regarded as object-centred neglect. Performance of the line cancellation test, which requires exploratory ability, was significantly better for the patients with the third pattern than for those with the second pattern. A significant difference was also observed between the two groups of patients in performance of the line bisection test, in which exploratory ability plays a more minor role. No significant difference was found in performance of the line cancellation and line bisection tests between the patients with the third and first patterns, in spite of remarkable differences in their copying performances. No distinctive characteristics were found for any group of patients as regards lesion, age, duration after onset, education, and WAJS scores. Therefore we concluded that in most of our patients with neglect, these diverse patterns of copying deficits resulted from different levels of neglect severity but not from different types of unilateral spatial neglect.     

Unilateral spatial neglect in Alzheimer's disease A line bisection study

Neuropsychological studies on Alzheimer's disease (AD) have rarely mentioned about unilateral spatial neglect in spite of widespread use of visuospatial tasks. We reported a 62-year-old woman with probable AD who showed moderate dementia with left unilateral spatial neglect and relatively preserved language function. An extensive line bisection study with either hand confirmed her having left unilateral spatial neglect. Single photon emission computed tomography revealed relative hypoperfusion in the right temporal and parietal regions. AD patients with disproportionate right hemisphere dysfunction may exhibit left unilateral spatial neglect if tested adequately in the stage of mild to moderate dementia. We consider that application of the line bisection test to AD patients contributes to estimation of their right hemisphere function.     

Spatial neglect in a patient with logopenic progressive aphasia

Spatial neglect and extinction are induced by posterior superior temporal and inferior parietal dysfunction. In patients with logopenic progressive aphasia (LPA) these structures are often degenerated, but there are no reports of these disorders being associated. A 53-year-old man with the signs of LPA revealed right-sided spatial neglect on line bisection and drawing tests as well as multimodal extinction. MRI showed left hemispheric posterior temporoparietal atrophy. Since injury to the core structures for these aphasic and attentional syndromes overlaps, patients with LPA should be screened for spatial neglect and extinction.     

Auditory neglect: what and where in auditory space

A sound that we hear in a natural setting allows us to identify the sound source and to localise it in space. Several lines of evidence indicate that the two aspects are processed in anatomically distinct cortical networks. Auditory areas that are part of the What or Where processing streams have been identified recently in man and in non-human primates. Comparison between anatomical and activation studies suggests that processing within either stream can be modulated by specific attentional factors. Attending to auditory events can be affected in neglect. Bisiach et al. (1984) described systematic directional errors to the ipsilesional space, which was considered a manifestation of hemispatial neglect and interpreted as a disruption of the neural network providing the internal representation of egocentric space. The other manifestation of auditory neglect is contralesional extinction in dichotic listening condition (Heilman and Valenstein, 1972). Recently two types of auditory neglect have been described, one corresponding to a primarily attentional deficit associated with basal ganglia lesions and the other to distortions of auditory space representations associated with parieto-prefrontal lesions (Bellmann et al., 2001). Based on studies of sound detection and sound recognition following hemispheric lesions we argue that the two types of neglect correspond to disturbed processing in either the What or the Where stream.     

From phenomena to models

Abstract

Over the past ten years there has been a dramatic expansion in the number of empirical studies concerned with the phenomena of neglect: for instance, there has been research into the systematic, directional errors made by neglect patients in line bisection, the omissions made in line cancellation tasks, the misidentifications in reading and object identification tasks, the errors made in copying and drawing from memory, the denial of neglect (anosognosia), and so forth. This work, whilst welcome, has led to a burgeoning amount of empirical detail that needs to be digested by any researcher coming into the field. In addition, much of the work has suggested that, within the general syndrome of neglect, patients can differ quite strikingly from one another. There are now well-documented dissociations between (for example) patients whose neglect is dependent on visual feedback and those whose neglect is dependent on kineasthetic feedback concerning the position of the limb in space (e.g. Tegnér & Levander, 1991), between neglect in cancellation tasks and anosagnosia (Bisiach, Perani, Vallar, & Berti, 1986), between neglect for peripersonal but not for extrapersonal space (Halligan & Marshall, 1991). This fractionation of symptoms underlines the important point that neglect is not a unitary disorder. A number of functionally different problems exist within (in the most general terms) the systems mapping between sensory input and motor output. And, though these problems are all characterised by being “spatial”, the “space” involved seems to vary according to the task and even the nature of the stimuli (see below). A major task for researchers is to document the nature of the different “spaces” that seem to be affected within particular patients.     

A stimulus-centered reading disorder for words and numbers: Is it neglect dyslexia?

A single case, RCG, showing a unilateral reading disorder without unilateral spatial neglect was studied. The disorder was characterized by substitutions of the initial (left) letters of words, nonwords and Arabic numbers, independently of egocentered spatial coordinates. MRI showed a bilateral lesion with the involvement of the splenium. Although, within the framework of the visual word recognition model proposed by Caramazza and Hillis (1990), RCG disorder could be defined as a stimulus-centered neglect dyslexia, we discuss the hypothesis of a dissociation in neural correlates and mechanisms between the syndrome of unilateral spatial neglect and such a unilateral reading disorder.     

Double dissociation between unilateral neglect and anosognosia

We report two patients presenting with a subacute right hemisphere stroke. These cases demonstrate a double dissociation between unilateral neglect and anosognosia for hemiplegia. The first patient suffered from a severe left hemiplegia associated with severe and persisting unilateral neglect. He appeared fully aware of his motor impairment. The second patient had a severe left hemiplegia, without any major sign of unilateral neglect on clinical tests nor on behavioural assessment. Nevertheless, he presented a severe and sustained anosognosia for hemiplegia. These case reports support the assumption that anosognosia and unilateral neglect, although they are frequently associated, may rely on independent mechanisms.     

Ineffective leftward search in line bisection and mechanisms of left unilateral spatial neglect

We examined the eye-fixation pattern of a patient with severe left unilateral spatial neglect who showed leftward searches of various extent in more than half of line bisection trials. Because of complete left homonymous hemianopia, he perceived only the segment of the line between its right endpoint and the point of the leftmost fixation. In the trials with leftward searches, he frequently placed the subjective midpoint on the right part of the perceived segment. In the trials without leftward searches, he placed it near the left extreme point of the perceived segment. For all these bisections, the subjective midpoint was constantly placed far to the right of the true midpoint of the line irrespective of the length perceived. We consider that in severe left unilateral spatial neglect, rightward attentional bias is the predominant factor that determines where to place the subjective midpoint. Transient attentional shift to the left may produce leftward searches, but it does not induce effective processing of line bisection.     

Auditory deficits in visuospatial neglect patients

Since the pioneering experimental work of Bisiach et al. (1984) on deficits in sound localisation associated with unilateral brain lesions and visual neglect, a number of systematic investigations have examined auditory processing in visuospatial neglect patients. Evidence from a variety of experimental paradigms has revealed some auditory deficits in detection and identification tasks, during bilateral stimulation; plus localisation deficits for single sounds. These deficits emerge predominantly for contra-lesional sounds, although some auditory disturbances applying to both contra- and ipsilesional sounds have also been documented. Here we review evidence suggesting that some of these auditory deficits arise in relatively high-level stages of spatial processing. In addition, we present new analyses showing that auditory deficits in identification and localisation tasks often correlate with clinical measures of visual neglect, across a variety of different studies and tasks. This empirical relation suggests that a disturbance of multisensory spatial processing may often account for the joint auditory and visual spatial deficits in neglect patients, although rarer dissociations between the modalities should also be considered.     

Clock Drawing in Children With Perinatal Stroke

BackgroundChildren with perinatal stroke may show evidence of contralateral spatial neglect. The goal of this study was to determine whether the Clock Drawing Test commonly used in adults to identify neglect would be effective in detecting neglect in children with perinatal stroke.MethodsThirty-eight individuals (age range 6-21 years) with left hemisphere or right hemisphere perinatal onset unilateral lesions and 179 age-matched controls were given a free-drawn Clock Drawing Test in a cross-sectional design. An adapted scoring system that evaluated right- and left-sided errors separately was developed as part of the investigation.ResultsChildren with right hemisphere lesions made a greater number of errors on both the right and left sides of the clock drawings in all age subgroups (6-8 years, 9-14 years, and 15-21 years) compared with controls. Children with right hemisphere lesions showed greater left and right errors in the younger groups compared with controls, with significantly poorer performance on the left at 6-8 years, suggestive of contralateral neglect. However, by ages 15-21 years, the right hemisphere lesion subjects no longer differed from controls.ConclusionsClock drawing can identify spatial neglect in children with early hemispheric damage. However, brain development is a dynamic process, and as children age, spatial neglect may no longer be evident. These findings demonstrate the limitations of predicting long-term outcome after perinatal stroke from early neurocognitive data. Children with perinatal stroke may require different neural pathways to accomplish specific skills or to overcome deficits, but ultimately they may have “typical” outcomes.     

Neglect-associated constructional disorders: a paradoxical phenomenon?

Five neglect patients without diffuse cognitive impairment or overt constructional disabilities were asked to bisect lines and rectangles and to copy rectangles bisected in their midplane. As a group, patients showed the usual rightward bias in bisecting lines and a milder deviation in bisecting horizontally-aligned rectangles, but showed a leftward deviation of the subjective midline in the copying task. This was due to drawing the left half shorter with respect to normal controls but three patients also drew the right half longer (the total length was the same as that of controls). A possible interpretation of rectangle copying results in these three patients is that they could create a representation of the stimulus to be copied accurately enough to reproduce its total length correctly but the subjective distribution of right and left space within that representation was unbalanced. However, specific experimental work is needed to verify why our patients with mild to moderate unilateral spatial neglect overrepresented the left side in a line bisection task and underrepresented it in a copying task.     

Line versus representational bisections in unilateral spatial neglect

OBJECTIVES: To clarify the mechanisms of left unilateral spatial neglect found in the bisection of lines after cueing to the left end point and to determine whether neglect occurs for the mental representation of a line. METHODS: A new representational bisection task was developed to eliminate the influence of the right segment of the physical line that would attract attention. Eight patients with typical left unilateral spatial neglect underwent line and representational bisection tasks on a computer display with a touch panel. In the line bisection with cueing, they bisected a line after touching the left end point. In the representational bisection, the patients were presented with a line until they touched the left end point. On the blank display, they pointed to the subjective midpoint of the erased line. The performances of the two bisection tasks were compared when the length and position of stimulus lines were varied. RESULTS: The rightward errors in the representational bisection were greater than or equivalent to those in the line bisection with cueing. The effect of line length in which the errors became greater for the longer lines was equally found in the line bisection with cueing and the representational bisection. This was confirmed in the condition where the right end point was placed at a fixed position and the line length was varied. CONCLUSIONS: After cueing to the left end point, rightward bisection errors of patients with neglect are not caused by overattention to the right segment of the physical line. Left neglect occurs mainly for the mental representation formed at the time of cueing or seeing the whole extent of a line.     

Rehabilitation by limb activation training reduces left-sided motor impairment in unilateral neglect patients: A single-blind randomised control trial

Limb activation treatment for unilateral neglect has been shown to be effective in several single case studies (Robertson, Hogg, & McMillan, 1998a; Robertson, North, & Geggie, 1992). Limb Activation Treatment (LAT) is based on the theoretical model that links different aspects of spatial representation in the brain. Specifically, proprioceptive representations are strongly linked to external visual representations, such as activation of one may have influences on the other. LAT is implemented using an automatic device—the limb activation device (LAD). This device encourages patients with left unilateral neglect to make small movements with the partly paralysed left side of their body. Thirty-nine patients with right brain damage following cerebrovascular accident (CVA) who showed left unilateral neglect, were randomly allocated to perceptual training plus LAT or to perceptual training alone. Both groups received training of 12 sessions of 45 min duration over a 12 week period; 36 of the 39 patients were successfully followed up blind at 3 months, a total of 32 were followed up blind at 6 months and 26 at 18–24 months. Outcome was assessed using a variety of standardised functional outcome and neuropsychological measures. LAT treatment was associated with significantly improved left-sided motor function, with effects lasting up to 18–24 months. The limb activation device can be used in the context of existing therapy with no additional therapy time. This study shows that LAT can produce enduring improvements in left-sided motor impairment in CVA patients suffering left unilateral neglect.     

The role of vision in spatial representation

A complex link exists between vision and unilateral spatial neglect (USN). Firstly, USN is not a perceptual deficit, secondly, USN is not necessarily accompanied by a visual deficit and finally, USN can be observed in non-visual modalities as well as in mental spatial imagery. This apparent supramodality of USN stands in sharp contrast to the fact that neglect signs are often more severe and more durable in the visual than in other sensory modalities (Chokron et al., 2002). The influence of vision on spatial representation has rarely been studied. In the present study we assessed six right brain-damaged patients suffering from left USN on two tasks involving spatial representations: a clock-drawing task and a drawing from memory task in two experimental conditions, with and without visual control. We confirm that even in mental imagery, the absence of visual feedback may decrease and even suppress left neglect signs (Bartolomeo and Chokron, 2001b; 2002). Since vision is largely involved in the orientation of attention in space, suppressing visual control could reduce the magnetic attraction towards the right ipsilesional hemispace and in this way could allow a re-orientation of attention towards the left neglected hemispace. We discuss the theoretical and therapeutic implications of these findings.     

Do neck-proprioceptive and caloric-vestibular stimulation influence covert visual attention in normals, as they influence visual neglect?

Neck-proprioceptive and caloric-vestibular stimulation have been shown to ameliorate the spatial bias exhibited by patients suffering from unilateral visual neglect. These interventions might in principle have their effect by biasing covert attention towards the neglected side. If so, the same interventions should also modulate covert attention in neurologically-intact subjects. However, we demonstrate here that neither neck-proprioception (vibration of left neck muscles) nor caloric-vestibular stimulation (injection of iced water into the left ear) affect covert visual attention in healthy individuals. These results from normals may distinguish between different accounts for unilateral neglect in patients. In particular, they argue against explanations of neglect solely in terms of a pathological misperception of body orientation within an otherwise normal neural representation of space.