Left Unilateral Spatial Neglect Research Articles

Mechanisms of unilateral spatial neglect in copying a single object

The present study examined 13 patients with typical left unilateral spatial neglect to explore the mechanisms of neglect in copying a single object. All patients identified the figure of a sunflower as a flower that had petals all around the central circle. Besides, in the free viewing of the flowers prepared by the examiner, 10 of the 13 patients could discriminate between the presence and absence of the left-sided petals. When copying the flower, however, they always left the left side unfinished without noticing the incompleteness. Whether perception in the left visual field was impaired or not was irrelevant to the performances in the copying and the free viewing of the flowers. We consider the mechanism of left unilateral spatial neglect in copying a flower as follows. Small leftward shift of attention may take place during the free observation of the stimulus flower. While copying, however, neglect patients pay attention exclusively to the right-sided petals they are drawing. The strong engagement of attention to the right side results in the lack of discovery of the left-sided omission. The close integration of attentional and premotor mechanisms seems to be crucial for the appearance of unilateral spatial neglect in copying a single object. Copyright © 1996 Elsevier Science Ltd

Appearance and disappearance of unilateral spatial neglect for an object: Influence of attention-attracting peripheral stimuli

We reported a dramatic phenomenon of appearance and disappearance of left unilateral spatial neglect for the same single object. In experiment 1, four patients with mild neglect who copied a single flower satisfactorily showed left neglect in copying of the same flower when it was accompanied with some peripheral stimuli. In experiment 2, we included three additional conditions to determine the stimulus component crucial for left neglect of the flower: a flower with a stem and a flower with either right or left peripheral stimuli were also used for copying. Overall results showed that neglect was most evident for the flower with the right peripheral stimuli. On the other hand, the presence of left stimuli provoked less severe neglect of the flower, which was as mild as that in the single flower condition. The results were explained in terms of an attentional mechanism underlying unilateral spatial neglect. When copying the flower with peripheral stimuli on both sides or on the right side, the stimuli on the right side might attract the patient's attention. Consequently, he exhibited left neglect on the central flower. On the other hand, neglect was less evident in the other conditions, since the figures did not include such attention-attracting stimuli on the right side

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-centered" 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 WAIS 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.

Analysis of patients with excellent motor recovery after large infarction in the middle cerebral artery territory including the cortex

We reported 6 cases of excellent motor recovery after a large infarction in the middle cerebral artery territory including the cortex. All patients were men (aged 67 to 80); 4 had left hemiplegia and 2 had right hemiplegia. They had abrupt onset of focal neurologic symptoms and signs, suggesting embolic stroke. The consciousness level, according to the Japan coma scale, was grade II in 4 patients and normal in the other 2. Atrial fibrillation was present in 4 patients and premature atrial and ventricular contractions were seen in 1 each. Hypertension was present in 3 patients and diabetes mellitus in 1. The motor plegia gradually improved after 1 to 3 days and almost completely disappeared at 12 days after onset. All patients were eventually able to walk alone without any aids. However, aphasia persisted in 2 patients with left hemispheric damage and left unilateral spatial neglect in 3 patients with right hemispheric damage. A cerebral blood flow analysis by single photon emission computed tomography, using [123I] isopropyliodoamphetamine or technetium 99m hexamethylpropylenamine oxime, demonstrated increased blood flow in the frontal lobe cortex surrounding the infarcted region in 5 patients. These patients showed good recovery from motor deficit, even though, motor symptoms did not begin to improve until 1 to 3 days after onset of stroke. We suggest that there is a subgroup of stroke patients, whose severe motor deficit starts to improve even 3 days after onset of a large infarction in the middle cerebral artery territory including the cerebral cortex.

Neuropsychological mechanisms of left unilateral spatial neglect associated with right hemisphere damage

Neuropsychological mechanisms of left unilateral spatial neglect associated with right hemisphere damage

Horizontal visual motion modulates focal attention in left unilateral spatial neglect.

Patients with unilateral spatial neglect are impaired in directing focal attention toward the contralesional side of space. Provision of static spatial cues on the neglected side has previously been shown to help overcome this deficit. Common movement of visual stimuli may also guide the allocation of spatial attention, although such effects have not been examined in patients with unilateral spatial neglect. Eleven patients with right hemisphere damage and clinical evidence of left unilateral spatial neglect, and 11 matched, healthy controls were tested on a task of horizontal line bisection. Lines were presented on a computer display, with a neutral, static, or slowly drifting, random dot background. Under conditions of motion, background stimuli drifted either leftward or rightward, across the full width of the display, at speeds that did not elicit optokinetic nystagmus or perceptual aftereffects. Controls were accurate in all conditions, and showed minimal effects of background conditions. By contrast, patients with left unilateral spatial neglect were sensitive to leftward background motion, showing a significant leftward shift in bisection error, relative to neutral, static, and rightward moving backgrounds. There was no significant effect of rightward motion in comparison with the neutral and static conditions. The extent to which patients were susceptible to the effects of background motion was not related to severity of unilateral spatial neglect, as measured by clinical tests. The benefits of leftward motion may reflect activity of preserved motion processing mechanisms, which provide input to an otherwise dysfunctional attentional network. The use of visual motion to assist in contralesionally guiding focal attention may be useful in the rehabilitation of unilateral spatial neglect.

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.

Unilateral spatial neglect

Abstract “Unilateral spatial neglect” or “hemispatial neglect” is a commonly used term for expressing the failure of brain damaged patients to attend to and explore stimuli presented in the space contralateral to their lesion (Heilman, Bowers, Valenstein, & Watson, 1987). Because unilateral spatial neglect is observed under conditions where movements of the eyes and head are permitted, trunk-hemispace, determined by the sagittal midplane of the body, is treated as the most important conceptual space for neglect (Heilman et al., 1987). However, the neglected space is not the unilateral half of space or hemispace. It is more accurate to state that there is a gradient in spatial locations subject to neglect: In left unilateral spatial neglect, the more a stimulus is located to the left, the more frequently it is neglected (Kinsbourne, 1987). There is no constant boundary between the neglected and non-neglected spaces for individual patients. We found that neglect patients could explore more to the left in the line cancellation task when motivated by numbering (Ishiai et al., 1990). Neglected space is also reported to be affected by demand on selective attention (Rapcsak, Verfaellie, Fleet, & Heilman, 1989) and by information implicit in stimulus configurations (Kartsounis & Warrington, 1989).

Improvement of left unilateral spatial neglect in a line extension task.

Patients with left unilateral spatial neglect following lesions that mainly involved the right parietal lobe performed a line extension task, extending a horizontal line leftward to double its original length. We examined line extension performances in the left and right hemispaces, as well as in the midline, to assess whether spatial conditions affected these performances. Whatever the severity of neglect found in the line bisection test, the line extension performances of the patients were almost accurate and comparable with those of normal controls across the three spatial conditions. The neglect patients executed movements in or toward the contralesional space as the task oriented their attention sufficiently to the left. The results suggest that the motor component, ie, directional hypokinesia, has little part in left unilateral spatial neglect due to right parietal lesions.

Clock-drawing test and unilateral spatial neglect.

We investigated the ability of 25 patients with left unilateral spatial neglect to make a clock face by putting numbers inside a printed circle. Impairment seen in this clock-drawing test did not parallel neglect severity as judged by results of the line-cancellation and line-bisection tests, as well as the copying of a daisy. The score for clock drawing correlated highly with the verbal WAIS score. Most neglect patients with a verbal IQ of 87 or more could draw a clock face fairly well and used planning in placing the numbers 12, 3, 6, and 9 before the others. In clock drawing, verbal intelligence may compensate for left unilateral spatial neglect. We therefore recommend use of the line-cancellation and line-bisection tests, as well as the copying test, but do not recommend use of the clock-drawing test in the diagnosis of left unilateral spatial neglect.

Analysis of left unilateral spatial neglect with a non-visual sensory-motor task

An experiment was conducted to analyze the space-movement processes which unilateral spatial neglect (USN) patients manifested. Three kinds of movement features were tested which were reported in previous studies; (a) general coarse response tendency, (b) hypokinesia in the disordered space-side, and (c) more frequent response toward the normal space-side. Five left USN patients with right brain damage were compared with five non-USN right brain damaged patients, and five normal controls. As an experimental movement task, a non-visual movement reproduction with regard to kinesthetic sensory modality was adopted. Subjects were blindfolded and asked to reproduce the criterion-movement (length of 10 cm) toward right hand side in space. Three different experimental spaces were used in relation to the subject's body positions; 'left space (range from left shoulder to median line)', 'right space (from median line to right shoulder)', and 'right-outside space (outside of right shoulder)'. The criterion-movement was presented to the subjects, and then they reproduced the movement in either one of these three spaces. Generally, the left USN patients reproduced movements with more errors and less accuracy when the execution side was in the 'left space'. The results confirmed the observation that left USN patients showed more frequent response toward the right hand side direction in the 'left space'. The left USN patients with lesions in frontal and/or basal ganglia regions showed larger errors in this task compared to the left USN patient whose lesion is localized in the parietal region in the right hemisphere.

Leftward search in left unilateral spatial neglect.

The authors' previous study with an eye camera revealed that when asked to mark the centre of a line patients with left unilateral spatial neglect persist in fixating a point on its right part and place the subjective midpoint there without searching leftwards. The present study examined the patterns of leftward search of nine patients with left unilateral spatial neglect when they were required to search for the left endpoint of the line after the bisection. The patients could search leftwards beyond the subjective midpoint to place the mark at the subjective left endpoint. The initial fixation in this search always fell near the point located to the left of the subjective midpoint by the distance between the subjective midpoint and the right endpoint of the line. In patients with severe neglect the search further to the left of this point was laborious and fell short of the true left endpoint in about 80% of the trials. Our results suggest that when asked to bisect a line patients with left unilateral spatial neglect subjectively see the line as it extends equally to either side of the point where they are going to mark the subjective midpoint.

Visual attentional disturbance with unilateral lesions in the basal ganglia and deep white matter

To elucidate the role of the basal ganglia and deep white matter in the visual attention mechanism, a new visual attention task was carried out by 15 patients, 9 with left-side and 6 with right-side basal ganglia and/or deep white matter damage without visual field defects, and by 12 normal subjects. Their reaction times were recorded in response to a random visual stimulation by pushing a button with the hand ipsilateral to the side of the lesion. All the patients with damage to the right side of the brain had a longer reaction time in the left space than in the right or middle space. With conventional test, only one of them showed left unilateral spatial neglect. Seven of the 9 patients with a left lesion had a significantly longer reaction time in the right space than in the left. None had unilateral spatial neglect. Both the right and left brain-damaged groups showed longer reaction times in both spaces, compared to the normal groups. There was no significant difference in reaction time among the control subjects. These findings suggest that the basal ganglia and deep white matter in each hemisphere play some role in directing visual attentional factors into both spaces. Visual attentional disturbance was highly evident even with left-side brain damage, and this kind of disturbance is not usually revealed with the current tasks used for testing unilateral spatial neglect.

Improvement of unilateral spatial neglect with numbering

We examined 8 patients with moderate to severe left unilateral spatial neglect by means of a series of line cancellation tasks. We asked the patients to cross out lines in the 1st trial, to number lines in the 2nd trial, and again to cross out lines in the 3rd trial. In the 2nd trial with numbering, all the patients showed improvement of left unilateral spatial neglect. Numbering involved the successive use of increasing numbers. This process seemed to motivate the patients to continue searching for another line, even at the point when they would be satisfied that they had completed the task if they used simple crossing-out. Insufficient motivation for visuospatial searching may play an important role in unilateral spatial neglect observed in cancellation tasks.

Effects of hand and spatial conditions on visual line bisection.

This study examined the effects of hand and spatial conditions on a visual line bisection task with normal right-handers and proposed a normal range of deviation for this task in middle and advanced age. Twenty-four normal dextrals in their fifties and sixties performed a visual line bisection task using either the left or right hand under three spatial conditions: at the midline and in the left and right hemispaces. Our results revealed that performance was significantly affected by the hand used but not spatial conditions: Left hand performance was significantly further leftward than right hand performance. There was no significant interaction between the hand and spatial conditions. The mean deviation of the right hand was 2.2% of the half line length to the right of the true center. The possibility of left unilateral spatial neglect should be considered if a patient bisects a line with a deviation greater than 10% of the half line length to the right.

Selective spatial attention and length representation in normal subjects and in patients with unilateral spatial neglect

The aim of this study was to assess whether perceptual representation along the horizontal axis is affected by hemispace position of the stimulus or by orienting attention to one side. Ten control subjects and 10 right brain damaged patients with left unilateral spatial neglect (USN) were asked to bisect lines of five lengths in three space positions (left, center, right) and under three cueing conditions (no cue, left cue, right cue). Normal controls showed significant displacement of bisection opposite to the side of hemispace presentation and toward the side of cueing. USN patients showed a bisection error toward the right end which increased with lines placed in the left hemispace and decreased with lines placed in the right hemispace and when attention was oriented toward the left side. We conclude that (1) In absence of cues normal subjects tend to overestimate the portions of space closer to their body midline; (2) both normal and USN patients tend to overestimate portions of space that they direct their attention to; (3) USN patients' performance without cueing is consistent with an attentional shift toward the right hemispace implying a gradient of overestimation of the right-most portions of space. A common neural substratum for directing attention and space representation can explain these findings.

左半側空間無視と半盲との関連について

Two cases of left unilateral spatial neglect (LUSN) were studied. One case is of a male patient, age 44. with serious LUSN accompanying left hemiparesis secondary to cerebral infarction. However, he revealed no hemianopsia in the visual field examination conducted on the Goldmann's kinetic perimeter, although an overall minor visual constriction was detected. The fact that his visual field examination did not bring out hemianopsia despite the presence of such a serious neglect syndrome, makes this case particularly significant for the purpose of finding out the exact nature of USN. The other case, male, age 64, was also examined on the same kinetic perimeter and revealed the presence of homonymous lower left quadrantic hemianopsia. After about a month's treatment of neglect, the patient made a remarkable progress in the simple tasks such as cancellation and explaining pictures. Then, the patient's visual field was examined again. It, however, demonstrated the persistent presence of homonymous lower left quadrantic hemianopsia. In other words, improvement in the degree of neglect exhibited no correlation with the change in the dimension of hemianopsia in the Case 2 patient.

A Simple Test of “Vigilance”

A simple test was designed to detect the disorder of vigilance, and its efficiency in clinical use was examined. The subject was instructed to tap a table continuously at the rate of once per second with a pencil held in his normal hand. The examiner, relying on a stopwatch, counted the number of tapping sounds per block of ten seconds for a duration of five minutes. As the index of this task, the mean and SD values of tapping sound numbers for thirty blocks (i. e., five minutes) were used. It was expected that performance of the task would fluctuate if vigilance was disturbed. For clinical examination, this task was applied to patients having left unilateral spatial neglect (left USN), who tend toward distraction and poor concentration in their daily life. In contrast to the control group, many patients in the left USN group showed a high mean and a large SD value. These results show that this task reflected the behavioral features of the left USN patient stated above. They also suggest that left USN patients cannot adequately control their own behavior continuously (i. e., sustained attention or vigilance disorder).

失文法を主症状とする右利き交叉性失語の１例

A case of crossed dextral aphasia characterized by agrammatism was reported. The patient,55-year-old purely right-handed man, a teacher of Japanese, developed left hemiparesis, slight left unilateral spatial neglect and aphasia because of cerebral infarction. CT scan displayed a large hypodense area in subcortical region of the right hemisphere. His speech showed slight dysarthria, literal paraphasias and agrammatism. The characteristics of the agrammatic speech were as follows : dropping out of grammatical morphemes (including joshi, auxiliary verbs and conjugation of verbs), good word-findings, lots of pauses in spite of long and well-constructed sentences. The writing had some literal paragraphias and agrammatism such as in speech. The way of writing was disorderly. Grammatical morphemes and verbs in part were regarded as representing speaker's thought and attitude essentially, and in case a speaker's tension to maintain his intention of speech was reduced, they would be apt to be dropped. We pointed out that the mechanism of writing disturbance of this case was different from non-crossed left hemisphere damaged aphasic's, and that such aphasic symptom as this case might represent a type peculiar to crossed dextral aphasia.

Recovery of behavioral abnormalities after right hemisphere stroke.

We studied recovery of function in 41 patients with right hemisphere stroke. Recovery was rapid for left neglect, prosopagnosia, anosognosia, and unilateral spatial neglect on drawing (USN). Recovery was slower for h mianopia, hemiparesis, motor impersistence, and extinction. Rates of recovery were intermediate for constructional apraxia and dressing apraxia. Sex had no influence on the rate of recovery. Younger patients recovered from prosopagnosia more rapidly than older patients. Patients with smaller lesions recovered more quickly from anosognosia, USN, and hemiparesis than patients with larger lesions. Patients with hemorrhages recovered more rapidly from constructional apraxia, neglect, and motor impersistence than patients with infarcts. Recovery of function and the factors influencing recovery can by studied systematically by life table methods.