Contralesional Stimuli Research Articles

Dorsal pulvinar inactivation leads to spatial selection bias without perceptual deficit

The dorsal pulvinar has been implicated in visuospatial attentional and perceptual confidence processing. Pulvinar lesions in humans and monkeys lead to spatial neglect symptoms, including an overt spatial saccade bias during free choices. However, it remains unclear whether disrupting the dorsal pulvinar during target selection that relies on a perceptual decision leads to a perceptual impairment or a more general spatial orienting and choice deficit. To address this question, we reversibly inactivated the unilateral dorsal pulvinar by injecting GABA-A agonist THIP while two macaque monkeys performed a color discrimination saccade task with varying perceptual difficulty. We used Signal Detection Theory and simulations to dissociate perceptual sensitivity (d-prime) and spatial selection bias (response criterion) effects. We expected a decrease in d-prime if dorsal pulvinar affects perceptual discrimination and a shift in response criterion if dorsal pulvinar is mainly involved in spatial orienting. After the inactivation, we observed response criterion shifts away from contralesional stimuli, especially when two competing stimuli in opposite hemifields were present. Notably, the d-prime and overall accuracy remained largely unaffected. Our results underline the critical contribution of the dorsal pulvinar to spatial orienting and action selection while showing it to be less important for visual perceptual discrimination.

Virtual and augmented reality gamification of visuospatial neglect treatment: therapists’ user experience

BackgroundVisuospatial neglect (VSN) is a cognitive disorder after stroke in which patients fail to consciously process and interact with contralesional stimuli. Visual Scanning Training (VST) is the recommended treatment in clinical guidelines. At the moment, several mixed reality versions of Visual Scanning Training (VST) are being developed. The aim of this study was to explore the opinions of end-users (i.e., therapists) on the use of Virtual Reality (VR) and Augmented Reality (AR) in VSN treatment.MethodsTherapists played one VR and two AR Serious Games, and subsequently filled out a questionnaire on User Experience, Usability, and Implementation.ResultsSixteen therapists (psychologists, occupational, speech, and physiotherapists) played the games, thirteen of them evaluated the games. Therapists saw great potential in all three games, yet there was room for improvement on the level of usability, especially for tailoring the games to the patient’s needs. Therapists’ opinions were comparable between VR and AR Serious Games. For implementation, therapists stressed the urgency of clear guidelines and instructions.DiscussionEven though VR/AR technology is promising for VSN treatment, there is no one-size-fits-all applicability. It may thus be crucial to move towards a plethora of training environments rather than a single standardized mixed reality neglect treatment.ConclusionAs therapists see the potential value of mixed reality, it remains important to investigate the efficacy of AR and VR training tools.

Monocular eye patching modulates ipsilesional reactive saccades and smooth pursuit in patients with left hemispatial neglect

Patients with hemispatial neglect show multiple oculomotor deficits like delayed contralesional saccade latencies, hypometric saccade amplitudes, and impaired smooth pursuit. We aimed to investigate whether modulation of superior colliculus (SC) activity via monocular eye patching improves neglect patients’ eye movements to the contralesional side of space. Thirteen neglect patients with left-hemispheric (LH) stroke, 22 neglect patients with right-hemispheric (RH) stroke, and 24 healthy controls completed a video-oculographic examination of horizontal smooth pursuit and reactive saccades twice, while the left or right eye was covered with an eye patch. Independent of the eye patch position, LH and RH patients showed enlarged saccade latencies toward contralesional stimuli. In addition, both during smooth pursuit and reactive saccades, RH patients made significantly fewer rightward saccades when the right than when the left eye was patched. Moreover, during reactive saccades, RH patients made significantly fewer right than left saccades, but only when the right eye was patched. These findings suggest that the ipsilesional eye patch modulated ipsilesional ocular performance in the RH group, presumably resulting from differences in SC activity. Yet, ipsilesional eye patching did not improve eye movements to the contralesional side of space, possibly due to the incomplete contralateral retinocollicular projection in humans.

Hierarchical psychophysiological pathways subtend perceptual asymmetries in Neglect

Stroke patients with left Hemispatial Neglect (LHN) show deficits in perceiving left contralesional stimuli with biased visuospatial perception towards the right hemifield. However, very little is known about the functional organization of the visuospatial perceptual neural network and how this can account for the profound reorganization of space representation in LHN.In the present work, we aimed at (1) identifying EEG measures that discriminate LHN patients against controls and (2) devise a causative neurophysiological model between the discriminative EEG measures. To these aims, EEG was recorded during exposure to lateralized visual stimuli which allowed for pre-and post-stimulus activity investigation across three groups: LHN patients, lesioned controls, and healthy individuals. Moreover, all participants performed a standard behavioral test assessing the perceptual asymmetry index in detecting lateralized stimuli. The between-groups discriminative EEG patterns were entered into a Structural Equation Model for the identification of causative hierarchical associations (i.e., pathways) between EEG measures and the perceptual asymmetry index.The model identified two pathways. A first pathway showed that the combined contribution of pre-stimulus frontoparietal connectivity and individual-alpha-frequency predicts post-stimulus processing, as measured by visual-evoked N100, which, in turn, predicts the perceptual asymmetry index. A second pathway directly links the inter-hemispheric distribution of alpha-amplitude with the perceptual asymmetry index. The two pathways can collectively explain 83.1% of the variance in the perceptual asymmetry index.Using causative modeling, the present study identified how psychophysiological correlates of visuospatial perception are organized and predict the degree of behavioral asymmetry in LHN patients and controls.

Detection of Stroke-Induced Visual Neglect and Target Response Prediction Using Augmented Reality and Electroencephalography.

We aim to build a system incorporating electroencephalography (EEG) and augmented reality (AR) that is capable of identifying the presence of visual spatial neglect (SN) and mapping the estimated neglected visual field. An EEG-based brain-computer interface (BCI) was used to identify those spatiospectral features that best detect participants with SN among stroke survivors using their EEG responses to ipsilesional and contralesional visual stimuli. Frontal-central delta and alpha, frontal-parietal theta, Fp1 beta, and left frontal gamma were found to be important features for neglect detection. Additionally, temporal analysis of the responses shows that the proposed model is accurate in detecting potentially neglected targets. These targets were predicted using common spatial patterns as the feature extraction algorithm and regularized discriminant analysis combined with kernel density estimation for classification. With our preliminary results, our system shows promise for reliably detecting the presence of SN and predicting visual target responses in stroke patients with SN.

A novel computerized assessment of manual spatial exploration in unilateral spatial neglect

ABSTRACT Unilateral spatial neglect is a neuropsychological syndrome commonly observed after stroke and defined by the inability to attend or respond to contralesional stimuli. Typically, symptoms are assessed using clinical tests that rely upon visual/perceptual abilities. However, neglect may affect high-level representations controlling attention in other modalities as well. Here we developed a novel manual exploration test using a touch screen computer to quantify spatial search behaviour without visual input. Twelve chronic stroke patients with left neglect and 27 patients without neglect (based on clinical tests) completed our task. Four of the 12 “neglect” patients exhibited clear signs of neglect on our task as compared to “non-neglect” patients and healthy controls, and six other patients (from both groups) also demonstrated signs of neglect compared to healthy controls only. While some patients made asymmetrical responses on only one task, generally, patients with the strongest neglect performed poorly on multiple tasks. This suggests that representations associated with different modalities may be affected separately, but that severe forms of neglect are more likely related to damage in a common underlying representation. Our manual exploration task is easy to administer and can be added to standard neglect screenings to better measure symptom severity.

Prism adaptation changes resting-state functional connectivity in the dorsal stream of visual attention networks in healthy adults: A fMRI study

Unilateral spatial neglect (USN) can be defined as a failure to orient to contra-lesional stimuli in the absence of either sensory or motor defects. Although the behavioral and clinical effects of prism adaptation (PA) are widely accepted, its underlying mechanisms are still controversial. However, recent neuroimaging and neurophysiological studies support the idea that PA affects the visual attention and sensorimotor networks including in the parietal cortex and cerebellum. We investigate the effect of PA on functional connectivity (FC) in attention and sensorimotor networks, evaluating changes of resting-state FC before and after PA in healthy individuals using functional magnetic resonance imaging (fMRI). MR sessions were conducted before PA, after PA (Post1), and 1 h after PA (Post2). The FC between the right frontal eye (FEF) field and the right intraparietal sulcus was significantly decreased at Post1 and that between the right FEF and the right anterior cingulate cortex was significantly increased after PA and recovered within 1 h. This is the first study to demonstrate transient changes of resting-state FC in the right dorsal attention network (DAN) by PA in healthy adults using fMRI. These results will contribute to the elucidation of the underling mechanism of PA therapy and to devising new therapies for USN and/or other higher cortical dysfunctions.

Frontal lesions predict response to prism adaptation treatment in spatial neglect: A randomised controlled study

ABSTRACTSpatial neglect commonly follows right hemisphere stroke. It is defined as impaired contralesional stimulus detection, response, or action, causing functional disability. While prism adaptation treatment is highly promising to promote functional recovery of spatial neglect, not all individuals respond. Consistent with a primary effect of prism adaptation on spatial movements, we previously demonstrated that functional improvement after prism adaptation treatment is linked to frontal lobe lesions. However, that study was a treatment-only study with no randomised control group. The current study randomised individuals with spatial neglect to receive 10 days of prism adaptation treatment or to receive only standard care (control group). Replicating our earlier results, we found that the presence of frontal lesions moderated response to prism adaptation treatment: among prism-treated patients, only those with frontal lesions demonstrated functional improvements in their neglect symptoms. Conversely, among individuals in the standard care control group, the presence of frontal lesions did not modify recovery. These results suggest that further research is needed on how frontal lesions may predict response to prism adaptation treatment. Additionally, the results help elucidate the neural network involved in spatial movement and could be used to aid decisions about treatment.

Dissociable components of spatial neglect associated with frontal and parietal lesions

Spatial neglect is a complex neuropsychological disorder, in which patients fail to detect and respond to contralesional stimuli. Recent studies suggest that these symptoms may reflect a combination of different component deficits, associated with different lesion substrates. Thus, damage to right lateral prefrontal and inferior parietal regions produce different degrees of left neglect on cancellation and line bisection tasks, respectively. Here we tested for dissociable behaviors across two tasks designed to assess distinct cognitive processes possibly mediating such components, in 14 patients with right focal lesion in either the frontal or parietal lobe. In the “distractor filtering” task, patients had to respond to a visual target presented centrally, with or without a lateralized distractor. Only frontal-lesioned patients showed a marked slowing of reaction times when a central target appeared with a simultaneous right distractor (compared to center and left distractor). In the “spatial coding” task, patients had to detect a target among successive visual stimuli presented horizontally with three sequence conditions (regular/predictive or irregular/non-predictive). Only parietal-lesioned patients were unable to benefit from the predictability of the target position, with similar reaction times across all sequence conditions. By contrast, frontal patients showed faster reaction times on trials with a regular succession of stimuli (compared to random order). Taken together, these results suggest that frontal damage may contribute to left inattention by disrupting top-down control and resistance to distractors on the ipsilesional side, whereas parietal damage may disrupt the maintenance of stable locations in space across gaze shifts or time. This further supports the notion that left neglect may arise as a combined breakdown or impaired connectivity between frontal and parietal mechanisms involved (respectively) in the selective control and memory storage components of spatial attention.

Attention as the ‘glue’ for object integration in parietal extinction

Patients with unilateral, parietal brain damage frequently show visual extinction, which manifests in a failure to identify contralesional stimuli when presented simultaneously with other, ipsilesional stimuli (but full awareness for single stimulus presentations). Extinction reflects an impairment of spatial selective attention, leaving basic preattentive processing unaffected. For instance, access to bilaterally grouped objects is usually spared in extinction, suggesting that grouping occurs at a stage preceding (in the patients: abnormally biased) spatial-attentional selection. Here, we reinvestigated this notion by comparing (largely between participants, but also within a single-case participant) conditions with objects that varied in their dominant direction of grouping: from the attended to the non-attended hemifield (data from Conci et al., 2009) versus from the non-attended to the attended hemifield (new data). We observe complete absence of extinction when shape completion extended from the attended hemifield. By contrast, extinction was not diminished when object groupings propagate from the unattended hemifield. Moreover, we found the individual severity of the attentional impairment (assessed by a standard “inattention” test) to be directly related to the degree of completion in the unattended hemifield. This pattern indicates that grouping can overcome visual extinction only when object integration departs from the attended visual field, implying, contrary to many previous accounts, that attention is crucial for grouping to be initiated.

Prism Adaptation in Rehabilitation? No Additional Effects of Prism Adaptation on Neglect Recovery in the Subacute Phase Poststroke: A Randomized Controlled Trial

Background. Patients with neglect ignore or respond slower to contralesional stimuli. Neglect negatively influences independence in activities of daily living (ADL). Prism adaptation (PA) is one of the most frequently studied treatments, yet there is little evidence regarding positive effects on neglect behavior in ADL. Objective. To assess whether PA in the subacute phase ameliorates neglect in situations of varying complexity. Methods. A total of 70 neglect patients admitted for inpatient stroke rehabilitation received either PA or sham adaptation (SA) for 2 weeks, with full access to standard treatment. There were 7 time-dependent measurements (baseline and 1-4, 6, and 14 weeks after start of treatment). The primary outcome was change of neglect as observed during basic ADL with the Catherine Bergego Scale (CBS). Secondary outcomes were changes in performance on a dynamic multitask (ie, the Mobility Assessment Course [MAC]) and a static paper-and-pencil task (ie, a shape cancellation task [SC]). Results. In all, 34 patients received PA and 35 SA. There were significant time-dependent improvements in performance as measured with the CBS, MAC, and SC (all F > 15.57; P < .001). There was no significant difference in magnitude of improvement between groups on the CBS, MAC, and SC (all F < 2.54; P > .113]. Conclusions. No beneficial effects of PA over SA in the subacute phase poststroke were observed, which was comparable for situations of varying complexity. Heterogeneity of the syndrome, time post–stroke onset, and the content of treatment as usual are discussed. Basic knowledge on subtypes and recovery patterns would aid the development of tailored treatment.

Role of the right inferior parietal cortex in auditory selective attention: An rTMS study

Selective attention is the process of directing limited capacity resources to behaviourally relevant stimuli while ignoring competing stimuli that are currently irrelevant. Studies in healthy human participants and in individuals with focal brain lesions have suggested that the right parietal cortex is crucial for resolving competition for attention. Following right-hemisphere damage, for example, patients may have difficulty reporting a brief, left-sided stimulus if it occurs with a competitor on the right, even though the same left stimulus is reported normally when it occurs alone. Such “extinction” of contralesional stimuli has been documented for all the major sense modalities, but it remains unclear whether its occurrence reflects involvement of one or more specific subregions of the temporo-parietal cortex. Here we employed repetitive transcranial magnetic stimulation (rTMS) over the right hemisphere to examine the effect of disruption of two candidate regions – the supramarginal gyrus (SMG) and the superior temporal gyrus (STG) – on auditory selective attention. Eighteen neurologically normal, right-handed participants performed an auditory task, in which they had to detect target digits presented within simultaneous dichotic streams of spoken distractor letters in the left and right channels, both before and after 20 min of 1 Hz rTMS over the SMG, STG or a somatosensory control site (S1). Across blocks, participants were asked to report on auditory streams in the left, right, or both channels, which yielded focused and divided attention conditions. Performance was unchanged for the two focused attention conditions, regardless of stimulation site, but was selectively impaired for contralateral left-sided targets in the divided attention condition following stimulation of the right SMG, but not the STG or S1. Our findings suggest a causal role for the right inferior parietal cortex in auditory selective attention.

Contralesional Trunk Rotation Dissociates Real vs. Pseudo-Visual Field Defects due to Visual Neglect in Stroke Patients.

In stroke patients, the clinical presentation of visual field defects (VFDs) is frequently accompanied by visual neglect, i.e., the inability to attend and respond to the contralesional space. However, the diagnostic discrimination between the lack of reactions to contralesional stimuli due to VFDs or visual neglect is challenging during clinical examination. This discrimination is particularly relevant, since both clinical pictures are associated with different therapeutic approaches and outcomes. The aim of this study was to systematically investigate the effectiveness of trunk rotation toward the contralesional side—a manipulation dissociating the coordinate system of the trunk from that of the head and eyes—in disentangling real VFDs from “pseudo-VFDs” that occur due to visual neglect. Twenty patients with a left-sided VFD after a right-hemispheric stroke (10 additionally showing visual neglect in neuropsychological testing, VFD + neglect; 10 without neglect, VFD) were tested with Goldmann perimetry in both standard and trunk rotation conditions. In the standard condition, both VFD and VFD + neglect patients showed a conspicuous narrowing of the left visual field. However, trunk rotation triggered strikingly different patterns of change in the two groups: it elicited a significant increase in visual field extension in the VFD + neglect group, but left visual field extension virtually unchanged in the VFD group. Our results highlight contralesional trunk rotation as a simple, viable manipulation to effectively and rapidly disentangle real VFDs from “pseudo-VFDs” (i.e., due to visual neglect) during clinical examination.

Mechanical pinprick pain in patients with unilateral spatial neglect: The influence of space representation on the perception of nociceptive stimuli.

Crossing the hands over the midline can reduce the perceived intensity of nociceptive stimuli applied onto the hands. It remains unclear to what extent intact representation of peripersonal space influences this effect. Here we used the crossed-hands paradigm in patients with unilateral spatial neglect, a neuropsychological condition characterized by the inability to detect, attend and respond to contralesional (most often left) stimuli, and spared ability to process stimuli in the non-affected space. Sixteen post-stroke patients without unilateral neglect and 11 patients with unilateral spatial neglect received punctate mechanical pinprick stimuli onto their crossed or uncrossed hands. We tested: (i) whether deficits in space representation reduce the possibility of observing 'crossed-hands analgesia', and; (ii) whether placing the contralesional hand, normally lying in the affected space in the healthy space would increase the number of detected stimuli. Our results showed that neglect patients did not exhibit 'crossed-hands' analgesia, but did not provide strong evidence for an improvement in the number of detected stimuli when the contralesional hand was in the healthy space. These findings uphold the notion that the perception of nociceptive stimuli is modulated by the relative position of the hands in space, but raise questions about the conditions under which these effects may arise. We show that deficits in space representation can influence the processing of mechanical pinprick stimuli. Our results raise several questions on the mechanisms underlying these effects, which are relevant for the clinical practice.

EXTINCTION: POSSIBLE INTERFERENCE OF TOP-DOWN INFORMATION. A CASE STUDY

Brain-damaged patients showing extinction are able to process stimuli presented on either hemispace, but fail to report contralesional stimuli when simultaneously presented with an ipsilesional stimulus. Extinction may occur stimuli of the same modality or between stimuli of different modalities (such as visual and tactile). This phenomenon has been interpreted as supramodal imbalance in stimulus competition for attention selection. However, recent studies have reported the existence of a complex interaction of competition-facilitation between visual and tactile information. We describe a patient (RP) who suffered from a brain damage on the right occipito-temporal cortical area. RP showed severe visual neglect associated with a rare case of extinction. He performed at ceiling on tactile extinction tasks when his eyes were closed, but showed dramatic tactile extinction when he looked directly at the hand being touched. The results as reflecting the existence of top-down mechanisms whereby the “absence” of visual information caused by visual neglect might have exacerbated underlying latent attentional biases.

Effects of attentional and cognitive variables on unilateral spatial neglect

Patients with visuospatial neglect when asked to cancel targets partially or totally omit to cancel contralesional stimuli. It has been shown that increasing the attentional demands of the cancellation task aggravates neglect contralesionally. However, some preliminary evidence also suggests that neglect might be worsened by engaging the patient in a demanding, non-spatial, cognitive activity (i.e. a mathematical task). We studied cancellation performance of 16 patients with right-hemisphere lesions, 8 with neglect, 8 without neglect, and 8 age-matched healthy control participants by means of five cancellation tasks which varied for the degree of attentional and/or high level cognitive demands (preattentive and attentive search of a visual target, searching for numbers containing the digit 3, even numbers, and multiples of 3).Results showed that attentive search of visual targets, relative to the preattentive search condition, aggravated neglect patients’ performance. Moreover, searching for multiples not only worsened spatial neglect contralesionally, but also slowed down performance of patients with right-hemisphere lesions without neglect.Our findings further demonstrate the presence of specific deficits of attention in neglect. In addition, the worse performance of patients without neglect in the ‘multiples of 3' task is consistent with the evidence that right-hemisphere lesions per se impair the ability to maintain attention (i.e. sustained attention). This suggests that the exacerbation of neglect during execution of a demanding, non-spatial, cognitive task might be explained by a deficit of sustained attention in addition to a selective deficit of spatial attention.

Multi-tasking uncovers right spatial neglect and extinction in chronic left-hemisphere stroke patients

Unilateral Spatial Neglect, the most dramatic manifestation of contralesional space unawareness, is a highly heterogeneous syndrome. The presence of neglect is related to core spatially lateralized deficits, but its severity is also modulated by several domain-general factors (such as alertness or sustained attention) and by task demands. We previously showed that a computer-based dual-task paradigm exploiting both lateralized and non-lateralized factors (i.e., attentional load/multitasking) better captures this complex scenario and exacerbates deficits for the contralesional space after right hemisphere damage. Here we asked whether multitasking would reveal contralesional spatial disorders in chronic left-hemisphere damaged (LHD) stroke patients, a population in which impaired spatial processing is thought to be uncommon. Ten consecutive LHD patients with no signs of right-sided neglect at standard neuropsychological testing performed a computerized spatial monitoring task with and without concurrent secondary tasks (i.e., multitasking). Severe contralesional (right) space unawareness emerged in most patients under attentional load in both the visual and auditory modalities. Multitasking affected the detection of contralesional stimuli both when presented concurrently with an ipsilesional one (i.e., extinction for bilateral targets) and when presented in isolation (i.e., left neglect for right-sided targets). No spatial bias emerged in a control group of healthy elderly participants, who performed at ceiling, as well as in a second control group composed of patients with Mild Cognitive Impairment. We conclude that the pathological spatial asymmetry in LHD patients cannot be attributed to a global reduction of cognitive resources but it is the consequence of unilateral brain damage. Clinical and theoretical implications of the load-dependent lack of awareness for contralesional hemispace following LHD are discussed.

Neuroplasticity for spontaneous functional recovery after neonatal hypoxic ischemic brain injury in rats observed by functional MRI and diffusion tensor imaging

For infants and children, an incredible resilience from injury is often observed. There is growing evidence that functional recovery after brain injury might well be a consequence of the reorganization of the neural network as a process of neuroplasticity. We demonstrate the presence of neuroplasticity at work in spontaneous recovery after neonatal hypoxic ischemic (HI) injury, by elucidating a precise picture in which such reorganization takes place using functional MRI techniques. For all 12 siblings, 6 rats were subjected to severe HI brain injury and 6 rats underwent sham operation only. Severe HI brain injury was induced to postnatal day 7 (p7) Sprague–Dawley rats according to the Rice–Vannucci model (right carotid artery occlusion followed by 150min of hypoxia with 8% O2 and 92% of N2). Brain activation maps along with anatomical and functional connectivity maps related to the sensory motor function were obtained at adult (p63) using blood oxygen level dependent (BOLD)-functional MRI (fMRI), resting state-functional MRI (rs-fMRI) and diffusion tensor imaging (DTI); each of these MRI data was related to sensory motor functional outcome. In-depth investigation of the functional MRI data revealed: 1) intra-hemispheric expansion of BOLD signal activation in the contralesional undamaged hemisphere for ipsilesional forepaw stimuli to include the M2 and Cg1 in addition to the S1 and M1 wide spreading in the anterior and posterior directions, 2) inter-hemispheric transfer of BOLD signal activation for contralesional forepaw stimuli, normally routed to the injured hemisphere, to analogous sites in the contralesional undamaged hemisphere, localized newly to the M1 and M2 with a reduced portion of the S1, 3) inter-hemispheric axonal disconnection and axonal rewiring within the undamaged hemisphere as shown through DTI, and 4) increased functional interactions within the cingulate gyrus in the HI injured rats as shown through rs-fMRI. The BOLD signal amplitudes as well as DTI and rs-fMRI data well correlate with behavioral tests (tape to remove). We found that function normally utilizing what would be the injured hemisphere is transferred to the uninjured hemisphere, and functionality of the uninjured hemisphere remains not untouched but is also rewired in an expansion corresponding to the newly formed sensorimotor function from both the contralesional and the ipsilesional sides. The conclusion drawn from the data in our current study is that enhanced motor function in the contralesional hemisphere governs both the normal and damaged sides, indicating that active plasticity with brain laterality was spontaneously generated to overcome functional loss and established autonomously through normal experience via modification of neural circuitry for neonatal HI injured brain.

Effects of broken affordance on visual extinction.

Previous studies have shown that visual extinction can be reduced if two objects are positioned to “afford” an action. Here we tested if this affordance effect was disrupted by “breaking” the affordance, i.e., if one of the objects actively used in the action had a broken handle. We assessed the effects of broken affordance on recovery from extinction in eight patients with right hemisphere lesions and left-sided extinction. Patients viewed object pairs that were or were not commonly used together and that were positioned for left- or right-hand actions. In the unrelated pair conditions, either two tools or two objects were presented. In line with previous research (e.g., Riddoch et al., 2006), extinction was reduced when action-related object pairs and when unrelated tool pairs were presented compared to unrelated object pairs. There was no significant difference in recovery rate between action-related (object-tool) and unrelated tool pairs. In addition, performance with action-related objects decreased when the tool appeared on the ipsilesional side compared to when it was on the contralesional side, but only when the tool handle was intact. There were minimal effects of breaking the handle of an object rather than a tool, and there was no effect of breaking the handle on either tools or objects on single item trials. The data suggest that breaking the handle of a tool lessens the degree to which it captures attention, with this attentional capture being strongest when the tool appears on the ipsilesional side. The capture of attention by the ipsilesional item then reduces the chance of detecting the contralesional stimulus. This attentional capture effect is mediated by the affordance to the intact tool.

Early sensory processing in right hemispheric stroke patients with and without extinction

While extinction is most commonly viewed as an attentional disorder and not as a consequence of a failure to process contralesional sensory information, it has been speculated that early sensory processing of contralesional targets in extinction patients might not be fully normal. We used a masked visuo-motor response priming paradigm to study the influence of both contralesional and ipsilesional peripheral subliminal prime stimuli on central target performance, allowing us to compare the strength of the early sensory processing associated with these prime stimuli between right brain damaged patients with and without extinction as well as healthy elderly subjects. We found that the effect of an informative subliminal prime in the left contralesional visual field on central target performance was significantly reduced in both right brain damaged patients with and without extinction. The results suggest that a low-level early sensory deterioration of the neural representation for contralesional prime stimuli is a general consequence of right hemispheric brain damage unrelated to the presence or absence of extinction. This suggests that the presence of a spatial bias against contralesional information is not sufficient to elicit extinction. For extinction to occur, this spatial bias might need to be accompanied by a pathological (non-directional) reduction of attentional capacity.