Increased attentional load moves the left to the right

Introduction: Unilateral brain damage can heterogeneously alter spatial processing. Very often brain-lesioned patients fail to report (neglect) items appearing within the contralesional space. Much less often patients mislocalize items’ spatial position. We investigated whether a top-down attentional load manipulation (dual-tasking), known to result in contralesional omissions even in apparently unimpaired cases, might also induce spatial mislocalizations. Method: Nine right-hemisphere-damaged patients performed three computer-based tasks encompassing different levels of attentional load. The side of appearance of visual targets had to be reported either in isolation or while processing additional information (visual or auditory dual task). Spatial mislocalizations (from the contralesional hemispace towards the ipsilesional unaffected one) were then contrasted with omissions both within and across tasks, at individual as well as at group level. Results: The representation of ipsilesional targets was accurate and not affected by dual-tasking requirements. Contralesional targets were instead often omitted and, under dual-task conditions, also mislocalized by four patients. Three cases reported a significant number of left targets as appearing on the right (alloesthesia). Two of these patients perceived more targets (albeit to a wrong spatial location) under dual- than under single-task load. In a fourth patient, increased visual load resulted in synchiria, the (mis)perception of single, contralesional targets as being two (one on each side). Conclusions: When the neural circuitry subtending spatial processing is damaged, an increase in task load can lead to either a disregard or a bias in the processing of contralesional hemispace. The spatial bias subtending mislocalizations seems to index a more severe deficit than neglect, as if contralesional space would be completely erased rather than merely ignored.     

Testing for neglect in right-hemispheric stroke patients using a new assessment battery based upon standardized activities of daily living (ADL)

Spatial neglect is most frequently observed after right-hemispheric stroke and is characterized by a failure to report, to respond, or to orient to stimuli presented to the contralesional side. Although many neglect patients show difficulties in accomplishing activities of daily living (ADL), to date the clinical assessment of neglect is based upon neuropsychological paper-and-pencil tests. Thus, essential information about the patient's functional status may be missed out.Accordingly, we aimed at developing a new neglect test battery that incorporates standardized ADL. Six conventional paper-and-pencil neglect tests and eight standardized ADL with newly developed neglect-specific scoring criteria and cut-off scores were administered to 68 right-hemispheric stroke patients.According to the neuropsychological tests 22 patients showed symptoms suggesting neglect, whereas 17 patients showed symptoms suggesting neglect according to the newly developed neglect test based upon ADL. Neglect-specific impairments in the neuropsychological tests were significantly associated with those in the ADL-based tests, although dissociations were observed in seven patients. Neglect severity (as reflected in the percentage of positive subtests) was comparable for both test batteries and both test instruments showed high interrater reliability. Voxel-based lesion-symptom mapping revealed that the severity of neglect according to the neuropsychological and ADL-based tests was significantly associated with lesions within right fronto-parietal networks.We conclude that the newly developed ADL-based neglect battery provides an economic and ecologically valid tool for the assessment of neglect. The test can be used to assess and quantify neglect in everyday activities, and thus to monitor realistically rehabilitative needs of neglect patients.     

Misrepresentation of horizontal space in left unilateral neglect: role of hemianopia.

BACKGROUND: Right-brain-damaged patients with left unilateral neglect are reported to misperceive the horizontal extension of contralesional stimuli as being shorter than that of ipsilesional stimuli. OBJECTIVE: To investigate the functional and anatomic correlates of horizontal space misrepresentation. METHODS: Eight right-brain-damaged patients with contralesional neglect and complete hemianopia (N+H+), nine right-brain-damaged patients with contralesional neglect and no visual field defect (N+H-), and five unilateral brain-damaged patients with contralesional complete hemianopia and no neglect (N-H+) reproduced a horizontal distance (10 cm) in the contralesional and ipsilesional hemispace. RESULTS: N+H+ patients overextended the distance contralesionally and underextended the same distance ipsilesionally. N+H- and N-H+ patients reproduced equivalent distances contralesionally and ipsilesionally. Compared with N+H- patients, N+H+ patients had a greater ipsilesional shift when bisecting horizontal lines; however, these two groups of patients had comparable neglect severity on multiple-item cancellation tasks. In the N+H+ group the area of maximal overlapping of the lesion was in the posterior cerebral lobes. CONCLUSION: Complete contralesional hemianopia after posterior brain damage is an important factor in determining misrepresentation of horizontal space in patients with left unilateral neglect.     

Effects of head rotation on space- and word-based reading errors in spatial neglect

Patients with right hemisphere lesions often omit or misread words on the left side of a text or the beginning letters of single words which is termed neglect dyslexia (ND). Two types of reading errors are typically observed in ND: omissions and word-based reading errors. The prior are considered as space-based omission errors on the contralesional side of the page, while the latter can be viewed as a kind of stimulus- or word-based reading errors where leftsided parts of a single perceptual entity (the word) are neglected. The head, trunk and eyes are part of a hypothetical egocentric reference frame that is aligned around our body and divides space into a left and right hemispace. Previous neglect studies have shown that head- and trunk-orientation significantly influence contralesional neglect. An open question is whether such egocentric manipulations also influence omissions and word-based errors in paragraph reading in ND. The current study investigated in a sample of right-hemisphere lesioned patients with ND vs. without ND and matched healthy control subjects the influence of head-rotation (HR) on both types of reading errors using controlled indented paragraph reading tests. Passive leftward HR significantly reduced omission errors on the left side of the text in ND, but had no effect on word-based reading errors. In conclusion egocentric manipulations like HR only appear to influence space-based attentional processes in neglect evident as omissions in paragraph reading but have no impact on those attentional processes involved in word identification evident as word-based errors in paragraph reading.     

Do supine position and deprivation of visual environment influence spatial neglect?

It has been suggested that in spatial neglect, placing the patient in a supine position and performing tasks in the dark would reduce the rightward bias in line bisection and cancellation tasks. However, these findings remain debated and have not been extended to other tasks such as reading or visual exploration. Here, in the same study, we examined the effect of body position (BP) and visual environment (VE) on relatively ecological tests of spatial neglect. Among 17 patients with right-hemisphere stroke, 12 were neglect and five were non-neglect in clinical tests. They were compared with 12 healthy control participants in four tasks: line bisection, text reading, number reading, and visual exploration. Tasks were performed on a computer screen in two BP (sitting and supine) and two VE (light and dark) conditions. We found that placing patients in darkness reduced contralesional omissions in the visual exploratory task and, to a smaller extent, in number reading. Conversely, the supine position did not influence performance, and even resulted in cognitive slowing, especially in reading. In conclusion, we confirmed that reducing visual information can improve performance, but only to a limited extent. This justifies strict control of peripheral visual information when exploring neglect patients. Conversely, positioning neglect patients in the supine position can have a discrete negative effect on cognitive functioning, and this effect must be taken into account during therapy.     

Comparison of the Behavioural Inattention Test and the Catherine Bergego Scale in assessment of hemispatial neglect

The objective of the study was to correlate visual and behavioural assessments of hemispatial neglect caused by cerebrovascular accident. We assessed 17 consecutive right-hemisphere stroke patients with hemispatial neglect: the Catherine Bergego Scale (CBS) was used to evaluate neglect in spontaneous behaviour and the conventional subtests of the Behavioural Inattention Test (BIT C) were used to assess visual neglect. The proportional severity of both visual and behavioural neglect was calculated in each individual patient. Dissociations were found between mild neglect in visual screening tasks and moderate or severe neglect in behaviour, although in most patients, neglect was equally evident in both tests. Only the line bisection subtest from the BIT correlated significantly with the CBS, yet both tests showed good internal consistency. The line bisection test and several items of the CBS were especially sensitive in detecting the combination of visual field deficit and hemispatial neglect. In conclusion, we propose that visual fields should always be assessed in patients with neglect because neglect may be exacerbated by a visual field deficit and this can cause prolonged functional disability in everyday life situations. Specific rehabilitation methods might also be needed in neglect with or without hemianopia.     

Visual Search and Visual Target Detection in Patients with Infarctions of the Left or Right Posterior or the Right Middle Brain Artery

We compared visual target detection and search performance of patient groups with infarctions of (1) the right middle brain artery (R-MBA) and with neglect; (2) the left posterior artery (L-PBA), (3) the right posterior artery (R-PBA), the latter two groups had contralesional hemianopias, or (4) with right hemisphere lesions without hemianopia or neglect. We found that: (1) The first three groups differed from the fourth (control) group in omissions. (2) The first three groups differed only in horizontal search but not in target detection. (3) No vertical search deficit was present for either group. (4) R-MBA patients found increasingly more targets in visual search from left to right, R-PBA patients had problems with the outermost contralesional column, L-PBA patients showed a generally slowed and more variable search pattern. Infarctions of left and R-PBA therefore resulted in different visual search patterns. The behavior of the patients with R-MBA is consistent with Kinsbourne's (1992) interactive inhibition theory of neglect.     

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.     

RehAtt – scanning training for neglect enhanced by multi-sensory stimulation in Virtual Reality

Background: There is a lack of effective treatment for neglect. We have developed a new training method, RehAtt?. The objective of this study was to determine whether RehAtt? improves spatial attention in chronic neglect after stroke. Methods: RehAtt? consists of a computer with monitor, 3D glasses, and a force feedback interface (Robotic pen) giving sensory motor activation to the contra-lesional arm. The software combines visual scanning training with multi-sensory stimulation in 3D virtual reality (VR) game environment. Fifteen stroke patients with chronic neglect (duration > 6 month) had repeated baseline evaluations to confirm stability of symptoms. There were no test–retest effects for any of the tests. Thereafter, all patients trained 15 h in RehAtt? (3 × 1 h for 5 weeks). A neglect test battery and Catherine Bergego Scale, CBS, were used to assess behavioral outcome after intervention. CBS was also used at a 6-month follow-up. Results: Using repeated measurement analysis improvements due to the training were found for Star cancellation test (p = 0.006), Baking tray task (p < 0.001), and Extinction test (p = 0.05). In the Posner task improvements were seen fewer missed targets (p = 0.024). CBS showed improvements in activities of daily life immediately after training (p < 0.01). After 6 months the patients still reported improvement in CBS. Conclusion: RehAtt? is a new concept for rehabilitation of neglect. Training with the VR-method improved spatial attention and showed transfer to improved spatial attention in activities of daily living in chronic neglect. Our results are promising and merit further studies.     

Caloric vestibular stimulation and postural control in patients with spatial neglect following stroke

The impact of spatial neglect remains a substantial challenge to patients undergoing rehabilitation following stroke. Beyond the relatively well-described implications for visuospatial function, neglect is increasingly shown to have a negative impact on the wider aspects of sensori-motor performance with corresponding implications for activities including gait and balance. Caloric vestibular stimulation (CVS) administered to the contralesional ear has previously been shown to improve performance in patients with spatial neglect. Here, in Experiment One, we investigated the effect of CVS on clinical measures of spatial neglect and postural control in three groups of patients following stroke; left brain damaged patients (LBD, n?=?6), right brain damaged patients without neglect (RBD–, n?=?6), and right brain damaged patients with neglect (RBD+?, n?=?6). While post-stimulation scores demonstrated an improvement for participants with spatial neglect, further analysis of postural scores indicated that improvement was selective for asymmetrical activities, with symmetrical activities remaining unchanged. We interpret these results with reference to the related problem of extinction which predicts that activities demanding synchronous bilateral activity (symmetrical activities) would cause greater difficulties for patients with neglect. In Experiment Two, we tested a further six RBD+ patients on the same measures following CVS to the ipsilesional (right) ear. There was no significant improvement in perceptual or postural scores. Our findings are supportive of previous studies that demonstrate improvement in perception and movement for patients with spatial neglect following contralesional CVS and suggest that these improvements may have clinical benefits.     

Effects of right-hemisphere cortical infarction and muscarinic acetylcholine receptor blockade on spatial visual attention performance in rats

The syndrome of hemispatial neglect is defined as an inability to report, respond or orient to stimuli contralateral to a cerebral lesion despite intact elementary sensory or motor function. This syndrome is typically observed after lesions of the right cerebral cortex, and has been associated with impairment of attention. We studied whether visual attention performance is impaired after right-hemisphere infarction in rats. Using a behavioural paradigm measuring spatial visual attention, we tested the effects of photothrombotic infarction to either the frontal cortex or the parietal cortex on attention performance. Since the cholinergic system is known to modulate attention performance, we additionally evaluated the role of cholinergic receptor blockade with scopolamine in our task paradigm. Our results show a transient response bias immediately after cortical infarction, with a decrease in contralesional responses and an increase in contralesional omissions after frontal infarction. Parietal infarction and systemic administration of scopolamine also resulted in a decrease in correct responses and an increase in omissions, but without a difference in side responding. In conclusion, right frontal infarction induces a transient impairment in contralesional spatial visual attention that we explain as left-sided neglect. Right parietal infarction and cholinergic blockade shows non-lateralized deficits in spatial visual attention, suggestive of global attentional impairment. We postulate that both effects of cortical infarction on attention performance may be related to cholinergic dysfunction. Our study confirms the role of frontal and parietal cortices in attention performance in rats, and corroborates the theory that attention performance is impaired in hemispatial neglect in human stroke patients.     

Personal neglect-a disorder of body representation?

The cognitive mechanisms underlying personal neglect are not well known. One theory postulates that personal neglect is due to a disorder of contralesional body representation. In the present study, we have investigated whether personal neglect is best explained by impairments in the representation of the contralesional side of the body, in particular, or a dysfunction of the mental representation of the contralesional space in general. For this, 22 patients with right hemisphere cerebral lesions (7 with personal neglect, 15 without personal neglect) and 13 healthy controls have been studied using two experimental tasks measuring representation of the body and extrapersonal space. In the tasks, photographs of left and right hands as well as left and right rear-view mirrors presented from the front and the back had to be judged as left or right. Our results show that patients with personal neglect made more errors when asked to judge stimuli of left hands and left rear-view mirrors than either patients without personal neglect or healthy controls. Furthermore, regression analyses indicated that errors in interpreting left hands were the best predictor of personal neglect, while other variables such as extrapersonal neglect, somatosensory or motor impairments, or deficits in left extrapersonal space representation had no predictive value of personal neglect. These findings suggest that deficient body representation is the major mechanism underlying personal neglect.     

Caloric stimulation in neglect: evaluation of response as a function of neglect type.

Contralesional neglect may be induced by either unawareness of contralesional stimuli (attentional neglect, AN) or failure to act in contralesional space (intentional neglect, IN). We examined whether contralesional cold caloric stimulation differentially affects AN versus IN. Patients with left-sided neglect (n = 16) from right-hemisphere lesions performed target cancellation and line bisection tasks. Using a video-based apparatus that reverses the right and left side of stimuli, patients with abnormal cancellation performance were divided into those with AN and those with IN. The 5 subjects with normal cancellation performance but rightward bisection bias were also separated into 2 neglect groups. Subjects performed cancellation or bisection tasks before and immediately after irrigation of the left auditory canal with ice water. Caloric stimulation induced brisk rightward nystagmus in all subjects. Subjects with AN cancelled more left-sided targets after stimulation than those with IN (p = .02). Whereas caloric stimulation significantly shifted bisection error leftward for both IN and AN groups (p < .0001), AN patients exhibited a greater magnitude of shift than the IN patients. While the basis for differential performance remains undefined, the data indicate that caloric stimulation influences AN more than IN.     

Ipsilesional 'where' with contralesional 'what' neglect

Whereas contralesional spatial neglect is usually caused by right temporo-parietal lesions, ipsilesional spatial neglect is induced primarily by right frontal lesions. This report describes a 73-year-old woman with a right inferior parietal lesion who on 'where' tasks (line bisection and midline pointing) demonstrated ipsilesional neglect, but on 'what' tests (gap vs. no-gap detection cancellation and clothing tape removal) demonstrated contralesional neglect. This 'what' and 'where' directional dissociation provides evidence for independent 'what' and 'where' attentional networks; however, the reason this parietal lesion causes this contralesional vs. ipsilesional spatial attentional 'what' and 'where' dichotomy remains to be determined.     

Re‐fixation and perseveration patterns in neglect patients during free visual exploration

The literature suggests that neglect patients not only show impairments in directing attention toward the left, contralesional space, but also present with perseverative behavior. Moreover, previous studies described re‐fixations during visual search tasks, and interpreted this finding as an impairment of spatial working memory. The aim of the present study was to study re‐fixations and perseverations (i.e., recurrent re‐fixations to same locations) during free visual exploration, a task with high ecological validity. We hypothesized that: (1) neglect patient would perform re‐fixations more frequently than healthy controls within the right hemispace; and, (2) the re‐fixation behavior of neglect patients would be characterized by perseverative fixations. To test these hypotheses, we assessed 22 neglect patients and 23 healthy controls, measuring their eye movements during free exploration of naturalistic pictures. The results showed that neglect patients tend to re‐fixate locations within the ipsilesional hemispace when they freely explore naturalistic pictures. Importantly, the saliency of discrete locations within the pictures has a stronger influence on fixation behavior within the contralesional than within the ipsilesional hemispace in neglect patients. Finally, the results indicated that, for re‐fixations, saliency plays a more important role within the contralesional than the ipsilesional hemispace. Moreover, we found evidence that re‐fixation behavior of neglect patients is characterized by frequent recurrent re‐fixations back to the same spatial locations which may be interpreted as perseverations. Hence, with the present study, we could better elucidate the mechanism leading to re‐fixations and perseverative behavior during free visual exploration in neglect patients.     

Left visuo-spatial neglect: a meaningless entity?

Six patients with unilateral right hemisphere damage are reported. Each patient performed two tasks that are traditionally regarded as diagnostic for left (peripersonal) visuospatial neglect: target cancellation and horizontal line bisection. Two patients were unimpaired on both tasks, and two were impaired on both. The two remaining patients showed a classic (and reliable) double-dissociation between the tasks. One of the patients who scored within normal limits on both cancellation and bisection showed left sided omissions on representational drawing. We argue that these results question the validity of any unitary concept of unilateral visuo-spatial neglect in peripersonal space.     

Optokinetic stimulation affects word omissions but not stimulus-centered reading errors in paragraph reading in neglect dyslexia

Patients with right hemisphere lesions often omit or misread words on the left side of a text or the initial letters of single words, a phenomenon termed neglect dyslexia (ND). Omissions of words on the contralesional side of the page are considered as egocentric or space-based errors, whereas misread words can be viewed as a type of stimulus-centered error where the left part of a single perceptual entity (the word) is neglected. Previous patient studies have shown that optokinetic stimulation (OKS) significantly modulates many facets of the neglect syndrome, including the subjective body midline, line bisection and size distortions. An open question is whether OKS can also influence omissions and stimulus-centered errors in paragraph reading in ND. The current study compared the influence of OKS on both types of reading errors using controlled indented paragraph reading tests in a group of 9 right-hemisphere lesioned patients with ND, 7 patients without ND and 9 matched healthy controls. Leftward OKS significantly reduced omissions on the left side of the text in ND. In contrast, the pattern of stimulus-centered reading errors remained unchanged. In conclusion egocentric manipulations like OKS only appear to influence space-based attentional processes evident as omissions in paragraph reading but have no impact on stimulus-centered attentional processes evident as word-based errors during paragraph reading in ND.     

Parallel interhemispheric processing in hemineglect: Relation to visual field defects

Parallel interhemispheric processing is required to explore our visual environment and to integrate visual information from both hemifields simultaneously. Damage to the right temporo-parietal cortex can disrupt such parallel processes and result in neglect and visual extinction of stimuli in the left contralesional visual space. Neglected or extinguished stimuli can still be processed, yet without reaching the patient's awareness. Such unconscious processing has been attributed to structurally intact primary visual areas in neglect. To study whether unconscious parallel processing depends on visual functional integrity, we compared the performance of neglect patients with visual field defects (VFDs) (n = 11) and hemianopic patients with partial or complete blindness of one visual hemifield (n = 11) on redundant targets effects (RTE). The RTE manifests as faster reaction times to redundant paired (two stimuli, one in each hemifield) than single stimulation (in one hemifield). We found RTEs, i.e., unconscious processing, in neglect patients but not in hemianopic patients. Furthermore, neglect patients showed large crossed–uncrossed differences (CUDs), i.e., faster response times to ipsi- than contralesional hemifield stimulation, reflecting a difference in processing speed for single stimuli in the two hemispheres that were correlated with VFDs and visual extinction. The finding that extinction, but not RTE, was correlated with the CUD suggests that under competitive bilateral stimulus conditions the delayed contralesional visual field input may not be detected by the intact left hemisphere, which presumably mediates the task given the impairment of the right hemisphere. By contrast, unconscious parallel processing of contralesional stimuli (RTE) occurred even when contralesional visual field input is lacking (VFD) or delayed (CUD) and is possibly mediated via subcortical visual pathways.     

Multimodal spatial orientation deficits in left-sided visual neglect

Patients with right-sided temporo-parietal lesions often show contralesional neglect. However, neglect patients may also show spatial-perceptual deficits beyond the bisection and space exploration deficits frequently assessed in the horizontal plane, that is, deficits in the judgment of the subjective visual vertical or horizontal. In a recent study (Kerkhoff, G. & Zoelch, C.. Disorders of visuo-spatial orientation in the frontal plane in patients with visual neglect following right or left parietal lesions. Exp. Brain Res., 1998;122:108-120) we found significant perturbations in the perception of these three visual spatial axes in patients with contralesional neglect from right or left parietal lesions. To examine if this finding extends also to another modality we investigated how neglect patients perform tasks of visual- and tactile-spatial judgments of axis-orientation in the frontal plane. Visual-spatial and tactile-spatial judgments of the subjective vertical, horizontal and a right oblique orientation were obtained from patients with and without neglect as well as from normal subjects. Patients with left neglect showed a significant, contraversive tilt of all three visual-spatial axes (+5.6 degrees to +9.5 degrees, counterclockwise), and of the three tactile-spatial axes as well (+5.2 degrees to +10.5 degrees, counterclockwise). In contrast, right and left hemisphere lesioned control patients without neglect and normal control subjects showed unimpaired visual and tactile-spatial judgments (constant errors: < 1.0 degree). Difference thresholds in the visual-spatial tasks and unsigned errors in the tactile-spatial tasks were selectively elevated in the neglect group in contrast to all other subject groups. Spatial orientation deficits were significantly associated with the severity of clinical neglect (r = 0.55-0.88), and with the patients' ambulation performance (r = 0.45-0.70). Furthermore, crossmodal axis orientation tests in two neglect patients showed a similar counterclockwise tilt of +5 degrees to +15 degrees, suggesting a similar spatial deficit in both modalities. Orientation judgments were significantly aggravated by a 25 degree-tilt of the head to the left, as tested in one neglect patient, while a comparable rightward head-tilt improved spatial judgments in both modalities. This suggests that spatial orientation judgments are significantly modulated by gravitational input in neglect patients. Together these results are interpreted as evidence for multisensory spatial orientation deficits in neglect patients which are modulated by head-position and are related to their accompanying postural impairment.