线等分试验与忽视症、偏盲的研究

目的了解中国老年人、忽视症、忽视症伴偏盲、单纯偏盲患者线等分试验的表现，探讨线等分试验对忽视症与偏盲的诊断价值及其神经心理学机制。方法对30例身体健康的中国老年人（正常对照组）以及73例单侧脑损伤患者（试验组）进行线等分试验检查，同时对73例单侧脑损伤患者进行忽视、偏盲检查。结果据忽视、偏盲检查结果将试验组分为单纯忽视症组、忽视症伴偏盲组和单纯偏盲组进行分析。正常对照组线等分试验无论左手、右手皆左向偏移，且左手偏移明显，两者相比差异有显著性（P〈0．001）。单纯忽视症组线等分试验多半偏向脑损伤的同侧，与正常对照组相比差异有显著性（P〈0．001）；忽视症伴偏盲组与单纯忽视症组线等分试验都偏向脑损伤的同侧，且前者偏移明显，两者相比差异有显著性（P〈0．001）；单纯偏盲组线等分试验偏向脑损伤的对侧，与正常对照组相比差异有显著性（P〈0．05）。结论线等分试验存在左、右手侧别的差别，线等分试验是忽视症较好的检查方法之一．线等分试验不完全和其它忽视症试验相关联．偏盲加重水平线索忽视程度，偏盲不影响线等分试验对忽视症的检测率。线等分试验可用来鉴别单纯偏盲和忽视。     

Processing of peripersonal and extrapersonal space using tools: evidence from visual line bisection in real and virtual environments

The dissociation between peripersonal space (within reaching) and extrapersonal space (beyond reaching) has been reported in studies using the line bisection task in left neglect patients and in healthy participants. Furthermore, this dissociation can be modulated by tool use. We conducted two experiments to compare line bisection in peripersonal (i.e., 30, 60 cm) and extrapersonal space (i.e., 90, 120 cm). Healthy participants bisected visual lines using sticks and a laser pointer, according to the experimental paradigm of Longo and Lourenco [On the nature of near space: Effects of tool use and the transition to far space. Neuropsychologia, 44, 977–981, 2006]. In Experiment 1 participants performed line bisection in a real environment, whereas in Experiment 2 participants performed line bisection in a virtual environment. Results from both experiments revealed an abrupt midpoint shift from the peripersonal to the extrapersonal space but only when a laser pointer was used. In addition, we confirmed that peripersonal space can be extended to extrapersonal space when participants used a stick. Notably, virtual reality can be a useful technique for studying the dissociation between peripersonal and extrapersonal space and their interaction by means of tool use.     

The effect of contextual auditory stimuli on virtual spatial navigation in patients with focal hemispheric lesions

Topographical disorientation is a frequent deficit among patients suffering from brain injury. Spatial navigation can be explored in this population using virtual reality environments, even in the presence of motor or sensory disorders. Furthermore, the positive or negative impact of specific stimuli can be investigated. We studied how auditory stimuli influence the performance of brain-injured patients in a navigational task, using the Virtual Action Planning–Supermarket (VAP-S) with the addition of contextual (“sonar effect” and “name of product”) and non-contextual (“periodic randomised noises”) auditory stimuli. The study included 22 patients with a first unilateral hemispheric brain lesion and 17 healthy age-matched control subjects. After a software familiarisation, all subjects were tested without auditory stimuli, with a sonar effect or periodic random sounds in a random order, and with the stimulus “name of product”. Contextual auditory stimuli improved patient performance more than control group performance. Contextual stimuli benefited most patients with severe executive dysfunction or with severe unilateral neglect. These results indicate that contextual auditory stimuli are useful in the assessment of navigational abilities in brain-damaged patients and that they should be used in rehabilitation paradigms.     

线索提示对忽视症患者线等分反转效应的影响

目的 研究线段长度、线索提示对忽视症患者线等分试验中反转效应的影响,以探讨注意、感觉、数量估计障碍等是否参与忽视症患者线等分试验中反转效应的神经机制.方法 试验对象为15例左侧空问忽视症患者和15名年龄、文化程度、MMSE评分等相匹配的健康人,进行不同线段长度和线索提示的线等分试验,观察线等分试验的偏移率和反转效应.健康对照组间分析比较用两独立样本t检验,各组内结果分析采用多因素的方差分析.结果 忽视症患者在单纯水平线等分中当线段长度分别为4、6、8、10、12 cm时,其偏移百分率(%)分别为-5.71±5.13、-2.48±8.83、-1.18±10.90、0.43±8.12、2.17±7.04,线段长度对偏移率影响有统计学意义(F=12.5,P＜0.01).线段长度小于10 cm时,9例表现为反转效应.相应长度线段右、左侧单侧增加线索提示,可削弱和增强忽视症患者线等分试验的反转效应[偏移百分率(%)分别为-3.93±7.04、2.43±6.34、4.93±5.19、6.49±3.36、6.38±4.18,P＜0.01;-10.93±8.85、-7.95±8.44、-4.14±8.37、-2.60±9.96、-1.57±10.67,P=0.03];双侧增加线索提示对反转效应影响无统计学意义[偏移百分率(%)分别为-5.93±7.76、-0.52±8.20、0.54±6.34、2.57±5.02、2.79±3.92,P=0.35].改变线索提示高度对反转效应影响无统计学意义(F=1.94,P=0.14).结论 在线等分试验中当线段长度较短时主观中点向左偏移,表现为反转效应,表明数量估计障碍参与反转效应的形成.在线等分试验中增加单侧线索提示对偏移率影响显著,表明注意导向参与反转效应的形成.改变线索提示高度对反转效应影响无统计学意义,表明感觉障碍在反转效应形成过程中不起独立因素.     

The effect of acute ethanol challenge on global visuospatial attention: Exaggeration of leftward bias in line bisection

Acute alcohol challenge has been associated with a selective impairment of right hemisphere function. A hallmark of visuospatial neglect syndrome is that patients with right hemisphere lesions misbisect horizontal lines far rightward of veridical centre. Neurologically intact participants misbisect lines with a systematic leftward bias (pseudoneglect). Neuroimaging studies in neurologically intact participants reveal predominant right hemisphere activation during performance of line bisection tasks. The current study assessed whether acute alcohol challenge alters global visuospatial attention. Participants (N=18; 10 male; strongly right-handed; mean age 23 years) engaged in a forced-choice tachistoscopic line bisection task in both ethanol challenge (mean BAC=.077) and no ethanol control conditions. Mean leftward bisection error in the control condition was ?0.238 degrees visual angle (1.05% line length), and leftward bisection error significantly increased (p=.001) under ethanol challenge (?0.333 degrees visual angle, 1.47% line length). Mean bisection precision in the control condition was 0.358 degrees visual angle (1.58% line length); bisection precision significantly deteriorated (p=.008) under ethanol challenge (0.489 degrees, 2.17% line length). Decreased bisection precision indicates that ethanol disrupts the fidelity of visuospatial performance. The exaggerated leftward bisection error implies that ethanol may exert a differential effect on left versus right hemispheric function with respect to the control of global visuospatial attention.     

Increased effect of target eccentricity on covert shifts of visual attention in patients with neglect

Debate continues regarding the mechanisms underlying covert shifts of visual attention. We examined the relationship between target eccentricity and the speed of covert shifts of attention in normal subjects and patients with brain lesions using a cued-response task in which cues and targets were presented at 2° or 8° lateral to the fixation point. Normal subjects were slower on invalid trials in the 8° as compared to 2° condition. Patients with right-hemisphere stroke with neglect were slower in their responses to left-sided invalid targets compared to valid targets, and demonstrated a significant increase in the effect of target validity as a function of target eccentricity. Additional data from one neglect patient (JM) demonstrated an exaggerated validity × eccentricity × side interaction for contralesional targets on a cued reaction time task with a central (arrow) cue. We frame these results in the context of a continuous ‘moving spotlight’ model of attention, and also consider the potential role of spatial saliency maps. By either account, we argue that neglect is characterized by an eccentricity-dependent deficit in the allocation of attention.     

Things that go bump in the right: the effect of unimanual activity on rightward collisions

Patients with right parietal damage and spatial neglect ignore the leftward features of their environment - causing them to bump into the left-side of doorways. In contrast, the normal population shows a mild attentional bias towards the left. Self-report measures show more collisions to the right in everyday settings. We sought to obtain a quantitative measure of lateralised bumping in a laboratory setting. Participants (n=276) walked through a narrow doorway and the experimenter recorded collisions. To investigate the association between bumping and paper-and-pencil tests of pseudoneglect, a line bisection task was administered. Unilateral activation of the hemispheres has been found to ameliorate the effects of spatial neglect. We investigated the effect of activation by asking participants to move their left-, right- or both-hands as they walked. In the both hands condition, which acted as a baseline, there were more right bumps than left bumps. The rightward bias was exasperated when the left hand moved, presumably because this movement activated the right hemisphere. In contrast, there were more left bumps when the right hand moved. The results demonstrate that bumping is not random and that we collide with the right side more often. Biases in bumping, however, were not related to biases in line bisection. The effect of hand-movement demonstrates that bumping is brought about by an imbalance of activation between the hemispheres.     

The greyscales task: a perceptual measure of attentional bias following unilateral hemispheric damage

The two cerebral hemispheres in humans have been suggested to control contralaterally opposed attentional biases. These biases may be revealed by unilateral hemispheric damage, which often causes contralesional spatial neglect, particularly when the right hemisphere (RH) is affected. Subtle attentional biases have also been observed in normal observers in tasks requiring judgements of horizontal spatial extent, brightness, numerosity and size. Here, we examined attentional biases for judging the darker of two left-right mirror-reversed brightness gradients under conditions of free viewing (the greyscales task). We compared performances of patients with damage to the RH (n=78) and left hemisphere (LH; n=20) with those of normal controls (n=20). Controls showed a small but significant leftward bias, implying a subtle asymmetry favouring the RH. In contrast, RH and LH patients showed extreme rightward and leftward biases, respectively, both of which differed significantly from that of controls. For the patient groups, performance on clinical tests of neglect (cancellation and line bisection) did not predict their greyscales scores. Pathological biases were present in patients without clinical neglect or visual field defects, suggesting that the attentional bias measured by the greyscales task can be dissociated from clinical neglect and visual sensory loss. The greyscales task offers an efficient means of quantifying pathological attentional biases in unilateral lesion patients; it is easy to administer and score, and may be particularly useful for clinical trials of recovery and rehabilitation following stroke.     

Touching base: The effect of participant and stimulus modulation factors on a haptic line bisection task

Acquiring information about our environment through touch is vital in everyday life. Yet very little literature exists about factors that may influence haptic or tactile processing. Recent neuroimaging studies have reported haptic laterality effects that parallel those reported in the visual literature. With the use of a haptic variant of the classical line bisection task, the present study aimed to determine the presence of laterality effects on a behavioural level. Specifically, three handedness groups including strong dextrals, strong sinistrals, and—the to-date largely neglected group of—mixed-handers were examined in their ability to accurately bisect stimuli constructed from corrugated board strips of various lengths. Stimulus factors known to play a role in visuospatial perception including stimulus location, the hand used for bisection, and direction of exploration were systematically varied through pseudo-randomisation. Similar to the visual domain, stimulus location and length as well as participants' handedness and the hand used for bisection exerted a significant influence on participants' estimate of the centre of haptically explored stimuli. However, these effects differed qualitatively from those described for the visual domain, and the factor direction of exploration did not exert any significant effect. This indicates that laterality effects reported on a neural level are sufficiently pronounced to result in measurable behavioural effects. The results, first, add to laterality effects reported for the visual and auditory domain, second, are in line with supramodal spatial processing and third, provide additional evidence to a conceptualisation of pseudoneglect and neglect as signs of hemispheric attentional asymmetries.     

Touching base: The effect of participant and stimulus modulation factors on a haptic line bisection task

Acquiring information about our environment through touch is vital in everyday life. Yet very little literature exists about factors that may influence haptic or tactile processing. Recent neuroimaging studies have reported haptic laterality effects that parallel those reported in the visual literature. With the use of a haptic variant of the classical line bisection task, the present study aimed to determine the presence of laterality effects on a behavioural level. Specifically, three handedness groups including strong dextrals, strong sinistrals, and-the to-date largely neglected group of-mixed-handers were examined in their ability to accurately bisect stimuli constructed from corrugated board strips of various lengths. Stimulus factors known to play a role in visuospatial perception including stimulus location, the hand used for bisection, and direction of exploration were systematically varied through pseudo-randomisation. Similar to the visual domain, stimulus location and length as well as participants' handedness and the hand used for bisection exerted a significant influence on participants' estimate of the centre of haptically explored stimuli. However, these effects differed qualitatively from those described for the visual domain, and the factor direction of exploration did not exert any significant effect. This indicates that laterality effects reported on a neural level are sufficiently pronounced to result in measurable behavioural effects. The results, first, add to laterality effects reported for the visual and auditory domain, second, are in line with supramodal spatial processing and third, provide additional evidence to a conceptualisation of pseudoneglect and neglect as signs of hemispheric attentional asymmetries.     

Light deprivation produces a therapeutic effect on neglect induced by unilateral destruction of the posterior parietal cortex in rats

Light deprivation has been found to produce accelerated recovery from severe multimodal neglect induced by unilateral destruction of medial agranular cortex, the rat analog of area 8 in humans. However, neglect in humans is most often produced by destruction of the parietal association cortex. Therefore, the present study examined whether light deprivation would produce accelerated recovery from severe multimodal neglect induced by unilateral destruction of the rodent analog of the parietal association cortex. Subjects received unilateral parietal association cortex lesions, and 4 h after surgery were tested for neglect of visual, tactile, and auditory stimuli. If severe neglect was obtained, subjects experienced either light deprivation, constant light, or a 12:12 light/dark cycle for 48 h. The results indicated that, relative to the other groups, the light deprivation group demonstrated significant accelerated recovery from neglect. Recovery was evident on the first post-light deprivation behavioral test, and was maintained for the 3 weeks of behavioral testing. The results provide further support for the therapeutic effects of light deprivation on neglect induced by cortical lesions when light deprivation is administered in the immediate postoperative period.     

Peripersonal spatial attention in children with spina bifida: associations between horizontal and vertical line bisection and congenital malformations of the corpus callosum, midbrain, and posterior cortex

Horizontal and vertical line bisection was studied in 129 children and adolescents between 8 and 19 years of age, one group (n = 32) of typically developing controls and one group (n = 97) with spina bifida (SBM), a neurodevelopmental disorder associated with dysmorphology of the corpus callosum, posterior cortex, and midbrain. For each participant, structural brain MRIs were analyzed qualitatively to identify beaking of the midbrain tectum and corpus callosum agenesis and hypoplasia and quantitatively by segmentation and volumetric analyses of regional cortical white and gray matter. Each group showed the line length effect, whereby greater estimation errors are made with longer lines. The group with SBM differed from controls in terms of both accuracy and variability of line bisection. Children with SBM showed pseudoneglect, attending more than controls to left hemispace. The extent of rightward bisection bias was unrelated to right posterior brain volumes, although an intact corpus callosum during development moderated and normalized the exaggerated leftward line bisection bias. More children with SBM than controls attended to inferior hemispace. A normal midbrain and greater posterior cortex volume during development moderated and normalized the downward bias. Children with SBM showed more intra-subject variability than controls. Line bisection in children with SBM reflects three deficits: an exaggerated attentional bias to left hemispace, an abnormal attentional bias to inferior hemispace; and a larger zone of subjective uncertainty in bisection judgments.     

Effects of emotional face cueing on line bisection in neglect: a single case study

One patient with left neglect (FM) and four right brain-damaged controls were tested on a line bisection task with pictures of neutral and emotional faces as unilateral cues. We thus manipulated the attentional salience of the cues (higher for emotional and lower for neutral faces) while keeping constant their physical dimensions. Our findings showed that left emotional faces were more effective than left neutral faces in reducing bisection errors only in FM. These data indicate that in the neglected hemispace cues bias attention rather than simply altering the perceptual point of balance of the line in the horizontal plane.     

Influences of time and spatial frequency on the perceptual bias: evidence for competition between hemispheres

Perceptual biases for various visual features, such as size, luminance and numerosity, have been implicated with a right-hemisphere dominance in spatial and attentional functions and/or an asymmetrical competition between the two hemispheres. However, the mechanisms underlying these biases are poorly understood. For example, it has been largely ignored that processing of those features is closely interconnected with spatial frequency filters. To probe the influence of spatial frequencies on perceptual biases, here we used a new gratingscales task in neurologically healthy participants. We found that perceptual bias was strongly influenced within a bandwidth of spatial frequencies and that this bias correlated with a bias for luminance depending on presentation time. Furthermore, our participants, divided into two subgroups of perceptually "sensitive" and "insensitive" performers, showed considerably different, presentation time-dependent patterns of perceptual bias. While both groups were biased to the left, insensitive performers more than sensitive performers, these biases varied in a mirror-symmetric manner such that one group showed peaks of bias at times when the other group showed minima and vice versa. Our data suggest that perceptual bias results from an interhemispheric competition within a right-dominant system responsive to spatial frequencies, luminance and perhaps other magnitudes including abstract ones.     

Route learning and shortcut performance in adults with intellectual disability: a study with virtual environments

The ability to learn routes though a virtual environment (VE) and to make a novel shortcut between two locations was assessed in 18 adults with intellectual disability and 18 adults without intellectual disability matched on chronological age. Participants explored two routes (A ⇔ B and A ⇔ C) until they reached a learning criterion. Then, they were placed at B and were asked to find the shortest way to C (B ⇔ C, five trials). Participants in both groups could learn the routes, but most of the participants with intellectual disability could not find the shortest route between B and C. However, the results also revealed important individual differences within the intellectual disability group, with some participants exhibiting more efficient wayfinding behaviour than others. Individuals with intellectual disability may differ in the kind of spatial knowledge they extract from the environment and/or in the strategy they use to learn routes.     

The effect of attentional scope on spatial relation processing: A case study

Patient NC showed impairment on several tasks making use of coordinate spatial information, while categorical processing was at control level. Her assessment of local and global features of visual stimuli indicated that she had a local bias of attention, whereas controls showed a global bias. Her problems with coordinate tasks can be explained by this reduced global attentional focus. These findings confirm previous reports suggesting that the processing of categorical spatial relations benefits from a small scope of attention, whereas a relatively large scope of attention enhances coordinate spatial relation processing.     

Space representation in children with dyslexia and children without dyslexia: Contribution of line bisection and circle centering tasks

Line bisection tasks (different space locations and different line lengths) and circle centering tasks (visuo-proprioceptive and proprioceptive explorations, with left or right starting positions) were used to investigate space representation in children with dyslexia and children without dyslexia. In line bisection, children with dyslexia showed a significant rightward bias for central and right-sided locations and a leftward bias for left-sided location. Furthermore, the spatial context processing was asymmetrically more efficient in the left space. In children without dyslexia, no significant bias was observed in central lines but the spatial context processing was symmetrical in both spaces. When the line length varied, no main effect was shown. These results strengthen the ‘inverse pseudoneglect’ hypothesis in dyslexia. In the lateral dimension of the circle centering tasks, children showed a response bias in the direction of the starting hand location for proprioceptive condition. For radial dimension, the children showed a forward bias in visuo-proprioceptive condition and more backward error in proprioceptive condition. Children with dyslexia showed a forward bias in clockwise exploration and more accurate performance in counterclockwise exploration for left starting position which may be in accordance with leftward asymmetrical spatial context processing in line bisection. These results underline the necessity to use the line bisection task with different locations as an appropriate experimental paradigm to study lateral representational bias in dyslexia. The contribution of the present results in the understanding of space representation in children with dyslexia and children without dyslexia is discussed in terms of attentional processes and neuroanatomical substrate.     

The effect of ipsilesional cues on line-bisection errors: the importance of predictive value

Patients with unilateral neglect were tested on a line-bisection task in which vertical lines were added to the ipsilesional or contralesional end. During some blocks, these vertical lines accurately predicted the horizontal length of the line, while on other blocks the vertical lines had little predictive value. We found that much of the improvement for ipsilesional vertical bars can be explained by their ability to predict the extent of the horizontal line. These results suggest that the predictive value of a ipsilesional cue is responsible for the reduction in line-bisection errors noted by Halligan and Marshall [Neuropsychologia 32 (1994) 13]. This effect of the predictive ipsilesional cue may work in combination with the expanded attentional effects posited by the ipsilesional contraction model that they proposed.     

Individual variation in line bisection: a study of four patients with right hemisphere damage and normal controls

In a previous study of line bisection, [Manning et al., Neuropsychologia 28, 647-655, 1990] we have shown that normal young adults show significant linear regressions of both transection displacement (TD) and standard deviation (SD) on line length. Furthermore, there was considerable individual variation in the magnitude of SDs and the direction and magnitude of TDs. These two sources of variance were uncorrelated. In the current study we provide a constructive replication of these findings on an older population that constitutes a more appropriate control sample for patients with stroke. The performance of four patients with right hemisphere stroke is then interpreted in terms of the constraints observed in normal subjects. All the patients showed qualitatively intact line bisection, but with quantitative impairments of varied severity. When analysed in two pairs, the patients also showed a double-dissociation between the magnitude of their mean transection displacements and the SDs of those means. This result is in conformity with the prediction based upon a lack of correlation between these two measures in normal subjects.     

Individual variation in line bisection: a study of normal subjects with application to the interpretation of visual neglect

Investigations of left visuo-spatial neglect are reviewed with special reference to line bisection performance. Attention is then drawn to inconsistencies in the direction and magnitude of transection displacements in group studies of normal controls. We argue that the lack of reliable information about normal mechanisms for line bisection makes it impossible to interpret pathological performance in neglect. Accordingly, we report a case-series of 22 normal young adults, each of whom bisects 10 lines of differing lengths 10 times each. There is very substantial between-subject variation in both the magnitude and direction of the linear regression of transection displacement on line length; there are likewise considerable differences in the magnitude of the linear regression of standard deviation on line length. These two sources of individual variation are uncorrelated. We propose a psychophysical theory of line bisection, and suggest that the basic mechanisms responsible for task-performance are qualitatively intact in visuo-spatial neglect, albeit quantitatively impaired.