Gradients of detection in neglect: comparison of peripersonal and extrapersonal space

Previous studies of target-cancellation performance in visuospatial neglect patients have reported lateral (left-right) and radial (near-far) gradients of attentional ability. The purpose of the present study was to replicate the reported attentional gradients in peripersonal space (within arms reach) and to examine whether lateral gradients of detection also appear in extrapersonal space (beyond arms reach), using equivalent tasks with no manual requirement. The relationship between radial gradients in peripersonal space and neglect severity (degree of lateral gradient) in extrapersonal space was also of interest. Right-hemisphere stroke subjects, with and without neglect, and healthy control subjects named visual targets on scanning sheets placed in peripersonal and extrapersonal space. The neglect group showed lateral gradients of increasing target detection from left to right in both peripersonal and extrapersonal space, which were not evident in the performance of either of the control groups. Double dissociations of neglect severity in peripersonal and extrapersonal space were also found in analyses of individual performance. Lesion analyses showed that peripersonal neglect was related to dorsal stream damage and extrapersonal neglect was related to ventral stream damage. Group analyses showed no significant radial gradients in peripersonal space in the three groups. In addition, while analyses of some individuals found significant near-far and far-near radial gradients, there was no correlation between radial gradients in peripersonal space and neglect severity in extrapersonal space. These results are discussed in terms of theorised hemispheric mechanisms of spatial attention and the relationship of neglect in the two co-ordinate spaces to the extent and location of damaged neurons in the right hemisphere.     

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.     

脑血管病的近体空间忽视

目的了解脑血管病所致脑损伤后近体空间忽视的发生率、忽视组脑损伤部位的分布及偏肓的发生情况，探讨忽视的临床表现特点及其机制。方法应用划消试验、临摹画图、自发画图、行为测查以及视野计对73例临床确诊的单侧脑损伤患者进行忽视筛查、视野检查，并对其损伤部位进行分析。结果在发病后3周评估，忽视的发生率为28．8％，其中右大脑半球忽视的发生率为40．0％，左大脑半球忽视的发生率为15．2％（P〈0．01）；发病后6周评估，忽视的发生率为19．2％，其中右大脑半球忽视的发生率为32．5％，左大脑半球忽视的发生率为3．03％（P〈0．01）。忽视组：涉及顶叶占61．9．5％，颞叶占52．4％，额叶占23．8％，枕叶占23．8％，基底节占19．0％，丘脑占14.3％，岛叶占9．52％，扣带回占4．76％。忽视组偏肓的发生率为52．3％，非忽视偏肓的发生率为11．5％（P〈0．01）。右大脑半球忽视程度较左大脑半球严重、持久，且非表现绝对偏侧忽视。结论空间忽视发生率主要受评估的方法和评估的时间影响，有大脑半球忽视的发生率高于左大脑半球；忽视组脑损伤部位主要见于顶叶、颞叶，忽视组偏盲的发生率高于菲忽视组。忽视的机制可能为空间一侧成分缺陷和非一侧成分缺陷交互作用而产生。     

Objects and their nouns in peripersonal space

In this study we investigated whether objects and their name evoke the activation of the same motor programs. In the first experiment participants had to make speeded responses based on the category of an object. They had to signal whether an object, presented visually, either within or outside their reachable space, was natural or manufactured, by making reach-to-precision or reach-to-power grasp responses. We found a compatibility effect between the response required by task, and the grip evoked by the object, for reachable space only. Nevertheless, this finding holds for artefacts and not for natural objects. In the second experiment, participants had to make reach-to-precision or reach-to-power grasp responses when deciding whether an object, presented either within or outside their reachable space, was congruent with a previously displayed word. In this case we found a compatibility effect between the response required by task and the grip evoked by the object's name, however this effect was not limited by participants’ reaching range. Our data suggest that objects and objects’ name likely correspond to different motor representations. That is, while the former seem to house both stable (i.e., shape and size) and temporary (i.e., orientation and distance with respect to the perceiver) action-relevant information, the latter seem to house only stable action-relevant information.     

Assessment of spatial neglect using computerised feature and conjunction visual search tasks

The purpose of this study was to assess the diagnostic sensitivity of tasks employing feature and conjunction visual searches in stroke patients with unilateral spatial neglect (USN).

Seventy-two stroke patients (right/left hemispheric damage with/without USN) and 39 healthy controls participated in the study. Hit rate and reaction time measures of feature and conjunction searches were tested using a newly developed computerised programme for the assessment of visual spatial attention (VISSTA). In addition, subjects received a set of diagnostic paper-and-pencil tests, and were also assessed for the impact of neglect on activities of daily living. Results indicated that the computerised test clearly differentiated between stroke patients and healthy controls, and between the different patient groups. USN patients showed significant contralesional disadvantage in both feature and conjunction visual search tasks. It is proposed that computerised assessment of visual search capacity is a useful and sensitive adjunct to standard paper-and-pencil tests of USN, with the advantage of testing responses based on attention shifts under a time constraint. The learning effects that limit the usefulness of paper-and-pencil tests in longitudinal studies are less likely to affect a computerised test, making it more suitable for monitoring treatment-induced or natural recovery by way of repeated testing.     

Object-based neglect for the near peripersonal space in drawing tasks

We report a patient with a right cortical and subcortical temporo-occipital lesion who showed spatial neglect mainly involving the left and the near peripersonal space. In drawing tasks the patient omitted the elements closer to him within each figure. A copying task with pairs of radially aligned line drawings demonstrated that the patient's radial neglect was based on within-object coordinates. This novel observation extends the egocentric–allocentric distinction to the radial dimension.     

A preliminary investigation into the psychometric properties of the Dublin Extrapersonal Neglect Assessment (DENA): A novel screening tool for extrapersonal neglect

Extrapersonal neglect is one clinical manifestation that can occur following stroke. Existing neglect assessment procedures have been criticised for lengthy administration and do not assess how extrapersonal space is affected. This study investigated the psychometric properties of a new, time-efficient screening tool for extrapersonal neglect. Full ethical approval was granted and consent obtained from 50 participants with first-time stroke. Participants were screened for extrapersonal neglect on two consecutive days by two raters using the Dublin Extrapersonal Neglect Assessment (DENA) to test inter-rater reliability. Construct validity of the DENA was investigated by comparing the DENA to the Catherine Bergego Scale (CBS). Additional analyses were calculated between the DENA and the extrapersonal items of the CBS (CBS-E). The kappa statistic, intraclass correlation coefficients (ICCs) and Bland Altman analyses were calculated to determine excellent inter-rater reliability (ICC 0.971, κ?=?.876) and significant correlation between the DENA and the CBS and CBS-E (ICC 0.870, 0.934, κ?=?.793, .833, respectively). Bland Altman analyses demonstrated acceptable levels of agreement between the DENA raters, and the DENA and CBS, with no systematic differences evident. The DENA provides clinicians with a quick and psychometrically sound screening tool for extrapersonal neglect to ensure this impairment is addressed in stroke rehabilitation.     

Prism adaptation improves visual search in hemispatial neglect

Visuomotor prism adaptation has been found to induce a lateral bias of spatial attention in chronic hemispatial neglect patients. Here, two experiments were conducted to explore the effects of 10° prism adaptation on visual search tasks and standard visual inattention tests. Baselines and intervention effects were measured on separate days for all patients. The first experiment explored whether prism adaptation affects performance on a time restricted visual search task (maximum 3500 ms presentation followed by visual and auditory feedback). No positive effects of prism adaptation were found on accuracy in visual search nor on traditional neglect tests. These results accord well with previous studies showing that increased cognitive load can lead to prism de-adaptation or unchanged performance following prism adaptation. Response times in visual search became faster following intervention but this was not the case for the standard neglect tests. In the second experiment, the same single-featured search task was used, but the participants had unlimited search time and received no feedback on their response. This time, the patients showed accuracy improvements in visual search and all four on regular neglect tests. Therapeutic effects lasted for at least 90-120 min. Response times on all tasks became faster after prism adaptation. The results are consistent with studies showing effects of prism adaptation on neuropsychological neglect tests and other attentional tasks that are not speeded or time restricted, where feedback is not provided, or are performed following non-feedback-based tasks. The current findings show that prism adaptation improves visual search in neglect and that these beneficial effects can disappear with feedback.     

Manual responses and saccades in chronic and recovered hemispatial neglect: a study using visual search

Hemispatial neglect affects both the ability to respond to targets on the contralesional side of space and to programme saccades to such targets. In the current study, we looked in detail at saccade programming and manual reaction times (RTs) in a range of visual search tasks, in which task difficulty was systematically increased by changing the nature of the distractors. In condition 1, the target was presented with no distractors. In the other conditions, displays contained three distractors that were changed across conditions to manipulate similarity to the target and so task difficulty.We tested two neglect patients, one chronic, one recovered along with two RCVA control patients and 12 age-matched controls. Both neglect patients studied could successfully execute saccades into the neglected field when the target was presented alone. However, a dissociation emerged between the two patients when the target was presented with distractor items. Patient ERs first saccade to target performance in the three search conditions revealed clear effects of distractor type. In contrast for the recovered patient AF, the left/right difference was present for all search displays and appeared to be constant regardless of distractor type. This differential pattern of behaviour may reflect the different underlying neural causes of the neglect in these patients. In the current study, the measurement of saccades allowed the task to be fractionated, and thus, reveal the action of multiple mechanisms controlling saccades in search.     

Effects of prismatic adaptation on judgements of spatial extent in peripersonal and extrapersonal space

Recent research has shown that visuomotor adaptation to a lateral displacement of the visual field induces significant perceptual aftereffects in normal observers, and in right hemisphere patients with spatial neglect [Neuroreport 11 (2000) 1899; Nature 395 (1998) 166]. These findings suggest that adaptive realignment following prism exposure induces a bias in visual space perception, even in tasks that require no visually guided motor response. Given recent neurophysiological and behavioural data suggesting independent visual representations for peripersonal and extrapersonal space, here we asked whether adaptive aftereffects extend beyond participants' immediate reaching space to stimuli presented beyond arms' reach (i.e. in extrapersonal space). Thirty-two participants underwent adaptive realignment to 10 degrees left- or right-displacing wedge-prisms. Before and after adaptation participants performed a visual landmark task that required estimation of the midpoint of horizontal line stimuli. There was a significant rightward shift in visual midpoint judgements following adaptation to left-deviating prisms, which was evident in both peripersonal and extrapersonal space. Paradoxically, a significant rightward shift also occurred following adaptation to right-deviating prisms, but only in extrapersonal space. We suggest that the pattern of adaptive aftereffects observed reflects the different reference frames used by participants to perform spatial judgements in peripersonal and extrapersonal space. We also propose that an underlying hemispheric asymmetry in the processing of spatial errors during adaptation may contribute to the direction of aftereffects in both normal observers, and in patients with unilateral lesions.     

Visual and motor neglect: Clinical and neurocognitive aspects

Attention allows us to prioritize the processing of external information according to our goals, but also to cope with sudden, unforeseen events. Attention processes rely on the coordinated activity of large-scale brain networks. At the cortical level, these systems are mainly organized in fronto-parietal networks, with functional and anatomical asymmetries in favor of the right hemisphere. Dysfunction of these right-lateralized networks often produce severe deficit of spatial attention, such as visual neglect. Other brain-damaged patients avoid moving the limbs contralateral to their brain lesion, even in the absence of sensorimotor deficits (motor neglect). This paper first summarizes past and current evidence on brain networks of attention; then, it presents clinical and experimental findings on visual and motor neglect, and on the possible mechanisms of clinical recovery.     

Spatial and temporal dynamics of visual search tasks distinguish subtypes of unilateral spatial neglect: Comparison of two cases with viewer-centered and stimulus-centered neglect

We developed a computerised test to evaluate unilateral spatial neglect (USN) using a touchscreen display, and estimated the spatial and temporal patterns of visual search in USN patients. The results between a viewer-centered USN patient and a stimulus-centered USN patient were compared. Two right-brain-damaged patients with USN, a patient without USN, and 16 healthy subjects performed a simple cancellation test, the circle test, a visuomotor search test, and a visual search test. According to the results of the circle test, one USN patient had stimulus-centered neglect and a one had viewer-centered neglect. The spatial and temporal patterns of these two USN patients were compared. The spatial and temporal patterns of cancellation were different in the stimulus-centered USN patient and the viewer-centered USN patient. The viewer-centered USN patient completed the simple cancellation task, but paused when transferring from the right side to the left side of the display. Unexpectedly, this patient did not exhibit rightward attention bias on the visuomotor and visual search tests, but the stimulus-centered USN patient did. The computer-based assessment system provided information on the dynamic visual search strategy of patients with USN. The spatial and temporal pattern of cancellation and visual search were different across the two patients with different subtypes of neglect.     

Action-specific remapping of peripersonal space

Peripersonal space processing in monkeys’ brain relies on visuo-tactile neurons activated by objects near, not touching, the animal's skin. Multisensory interplay in peripersonal space is now well documented also in humans, in brain damaged patients presenting cross-modal extinction as well as in healthy subjects and typically takes the form of stronger visuo-tactile interactions in peripersonal than far space. We recently showed in healthy humans the existence of a functional link between voluntary object-oriented actions (Grasping) and the multisensory coding of the space around us (as indexed by visual-tactile interaction). Here, we investigated whether performing different actions towards the same object implies differential modulations of peripersonal space. Healthy subjects were asked to either grasp or point towards a target object. In addition, they discriminated whether tactile stimuli were delivered on their right index finger (up), or thumb (down), while ignoring visual distractors. Visuo-tactile interaction was probed in baseline Static conditions (before the movement) and in dynamic conditions (action onset and execution). Results showed that, compared to the Static baseline both actions similarly strengthened visuo-tactile interaction at the action onset, when Grasping and Pointing were kinematically indistinguishable. Crucially, Grasping induced further enhancement than Pointing in the execution phase, i.e., when the two actions kinematically diverged. These findings reveal that performing actions induce a continuous remapping of the multisensory peripersonal space as a function of on-line sensory-motor requirements, thus supporting the hypothesis of a role for peripersonal space in the motor control of voluntary actions.     

Dissociation in the recovery from neglect dyslexia and visuospatial unilateral neglect: a case report

The recovery of the ability to read of a patient affected by persistent visuospatial neglect suggests the functional independence of the two phenomena. Neglect dyslexia seems to be an example of a dissociation between an implicit and explicit knowledge of the characteristics of the stimulus.

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Sommario Il recupero della capacità di lettura in un paziente con persistente neglect visuo-spaziale suggerisce l'indipendenza funzionale dei due fenomeni. La neglect dyslexia sembra costituire un esempio di dissociazione tra conoscenza implicita ed esplicita delle caratteristiche dello stimolo.

     

Hemispatial neglect and visual search: a large scale analysis

Visual search tasks have standardly been divided into two categories: those in which the target is detected through a serial, attention-driven search and those in which the target is detected rapidly in parallel and, apparently, without attentional processing. Several studies have examined this distinction in patients with hemispatial neglect with the clear prediction that the former, but not the latter, should be impaired. These studies, however, have proved inconclusive. We have addressed this issue in a large sample of patients with unilateral hemispheric infarcts to the left or right hemisphere. In addition to measuring the patients' performance on both types of visual search tasks, we documented the presence and severity of neglect and of visual field defects in these same individuals. Patients with brain-damage with or without accompanying neglect were impaired at searching for the contralateral target on both forms of visual search, relative to normal control subjects, although this deficit was magnified in individuals with neglect and was also exacerbated by the presence of hemianopia. This pattern was also more pronounced in individuals with right-than with left-hemisphere lesions. The findings not only clarify the contradictory neuropsychological data but also provide clear evidence for the involvement of attentional processing in all forms of visual search.     

Visuospatial neglect in near and far space: dissociation between line bisection and letter cancellation

The differential performance on a line bisection and a cancellation task in near and far space was studied. A group of 10 patients with severe left-sided visuospatial neglect and a group of 10 right-brain damaged patients without neglect were examined. The stimuli were presented at a distance of 60 cm (near space) and 160 cm (far space), respectively, and corrected for visual angle. In the line bisection task, patients were asked to point to the estimated line centre with a pencil (near space) or a stick (far space). In the cancellation task, patients pointed to all target stimuli they could detect using either a pencil (near space) or a stick (far space). Most patients with left hemineglect showed a more prominent neglect in far space as compared to near space for the line bisection task, whereas no difference of performance between near and far space was found in the control patients. In contrast, no group showed a distance effect in the cancellation task. The observation that only line bisection is influenced by the distance of the stimulus suggests that line bisection and cancellation are processed differentially. It is proposed that line bisection requires an allocentric reference system focusing attention on objects, whereas cancellation tasks are based on an egocentric reference system responsible for visuospatial attention. Our results indicate that distance changes perception within the allocentric but not within the egocentric system.     

Effects of emotional and non-emotional cues on visual search in neglect patients: evidence for distinct sources of attentional guidance

In normal observers, visual search is facilitated for targets with salient attributes. We compared how two different types of cue (expression and colour) may influence search for face targets, in healthy subjects (n = 27) and right brain-damaged patients with left spatial neglect (n = 13). The target faces were defined by their identity (singleton among a crowd of neutral faces) but could either be neutral (like other faces), or have a different emotional expression (fearful or happy), or a different colour (red-tinted). Healthy subjects were the fastest for detecting the colour-cued targets, but also showed a significant facilitation for emotionally cued targets, relative to neutral faces differing from other distracter faces by identity only. Healthy subjects were also faster overall for target faces located on the left, as compared to the right side of the display. In contrast, neglect patients were slower to detect targets on the left (contralesional) relative to the right (ipsilesional) side. However, they showed the same pattern of cueing effects as healthy subjects on both sides of space; while their best performance was also found for faces cued by colour, they showed a significant advantage for faces cued by expression, relative to the neutral condition. These results indicate that despite impaired attention towards the left hemispace, neglect patients may still show an intact influence of both low-level colour cues and emotional expression cues on attention, suggesting that neural mechanisms responsible for these effects are partly separate from fronto-parietal brain systems controlling spatial attention during search.     

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.     

Everyday use of the computer mouse extends peripersonal space representation

Auditory and tactile stimuli are integrated within a limited space around the body to form an auditory peripersonal space (APPS). Here we investigate whether the APPS representation around the hand can be extended through the use of a common technological tool such as the computer mouse. When using a mouse, an action occurring in the space around the hand has a distal effect in the space defined by the computer screen; thus, the mouse virtually links near and far space. Does prolonged experience with the mouse durably extend APPS representation to the far space? We examined 16 habitual mouse users to determine whether a sound presented near the right hand or near the computer screen affected reaction times to a tactile target at the hand. When subjects sat in front of the computer, without holding the mouse, they responded faster to tactile stimuli when sounds were presented near the hand rather than near the screen, consistent with a normal segregation of APPS around the hand. In contrast, when subjects either actively used or even passively held the mouse, the difference between the effects of near and far sounds disappeared, thus showing an extension of the APPS toward the far space. This effect was selective for the effector used to operate the mouse: if tactile stimuli were presented on the left hand, rarely used to act upon the mouse, a sound presented near the hand speeded up reactions times when subjects both held and did not hold the mouse in their left hand.