Visuospatial memory in apraxia: Exploring quantitative drawing metrics to assess the representation of local and global information.

Neuropsychological evidence suggests that visuospatial memory is subserved by two separable processing systems, with dorsal underpinnings for global form and ventral underpinnings for the integration of part elements. Previous drawing studies have explored the effects of Gestalt organisation upon memory for hierarchical stimuli, and we here present an exploratory study of an apraxic dorsal stream patient's (MH) performance. We presented MH with a stimulus set (previously reported by Riddoch et al., Cognitive Neuropsychology, 20(7), 641-671, 2003) and devised a novel quantitative scoring system to obtain a finer grain of insight into performance. Stimuli possessed either good or poor Gestalt qualities and were reproduced in a copy condition and two visual memory conditions (with unlimited viewing before the model was removed, or with 3 s viewing). MH's copying performance was impaired in comparison to younger adult and age-matched older adult controls, with a variety of errors at the local level but relatively few at the global level. However, his performance in the visual memory conditions revealed impairments at the global level. For all participants, drawing errors were modulated by the Gestalt qualities of the stimuli, with accuracy at the global and local levels being lesser for poor global stimuli in all conditions. These data extend previous observations of this patient, and support theories that posit interaction between dorsal and ventral streams in the representation of hierarchical stimuli. We discuss the implications of these findings for our understanding of visuospatial memory in neurological patients, and also evaluate the application of quantitative metrics to the interpretation of drawings.

Recovery of Visuospatial Neglect Subtypes and Relationship to Functional Outcome Six Months After Stroke.

Background/Objective. This study aims to investigate how complex visuospatial neglect behavioural phenotypes predict long-term outcomes, both in terms of neglect recovery and broader functional outcomes after 6 months post-stroke. Methods. This study presents a secondary cohort study of acute and 6-month follow-up data from 400 stroke survivors who completed the Oxford Cognitive Screen's Cancellation Task. At follow-up, patients also completed the Stroke Impact Scale questionnaire. These data were analysed to identify whether any specific combination of neglect symptoms is more likely to result in long-lasting neglect or higher levels of functional impairment, therefore warranting more targeted rehabilitation. Results. Overall, 98/142 (69%) neglect cases recovered by follow-up, and there was no significant difference in the persistence of egocentric/allocentric (X2 [1] = .66 and P = .418) or left/right neglect (X2 [2] = .781 and P = .677). Egocentric neglect was found to follow a proportional recovery pattern with all patients demonstrating a similar level of improvement over time. Conversely, allocentric neglect followed a non-proportional recovery pattern with chronic neglect patients exhibiting a slower rate of improvement than those who recovered. A multiple regression analysis revealed that the initial severity of acute allocentric, but not egocentric, neglect impairment acted as a significant predictor of poor long-term functional outcomes (F [9,300] = 4.742, P < .001 and adjusted R2 = .098). Conclusions. Our findings call for systematic neuropsychological assessment of both egocentric and allocentric neglect following stroke, as the occurrence and severity of these conditions may help predict recovery outcomes over and above stroke severity alone.

Handgrip Based Action Information Modulates Attentional Selection: An ERP Study.

Prior work shows that the possibility of action to an object (visual affordance) facilitates attentional deployment. We sought to investigate the neural mechanisms underlying this modulation of attention by examining ERPs to target objects that were either congruently or incongruently gripped for their use in the presence of a congruently or incongruently gripped distractor. Participants responded to the presence or absence of a target object matching a preceding action word with a distractor object presented in the opposite location. Participants were faster in responding to congruently gripped targets compared to incongruently gripped targets. There was a reduced N2pc potential when the target was congruently gripped, and the distractor was incongruently gripped compared to the conditions where targets were incongruently gripped or when the distractor, as well as target, was congruently gripped. The N2pc results indicate that target selection is easier when action information is congruent with an object's use.

Unconscious Familiarity-based Color-Form Binding: Evidence from Visual Extinction.

There is good evidence that early visual processing involves the coding of different features in independent brain regions. A major question, then, is how we see the world in an integrated manner, in which the different features are "bound" together. A standard account of this has been that feature binding depends on attention to the stimulus, which enables only the relevant features to be linked together [Treisman, A., & Gelade, G. A feature-integration theory of attention. Cognitive Psychology, 12, 97-136, 1980]. Here we test this influential idea by examining whether, in patients showing visual extinction, the processing of otherwise unconscious (extinguished) stimuli is modulated by presenting objects in their correct (familiar) color. Correctly colored objects showed reduced extinction when they had a learned color, and this color matched across the ipsi- and contralesional items (red strawberry + red tomato). In contrast, there was no reduction in extinction under the same conditions when the stimuli were colored incorrectly (blue strawberry + blue tomato; Experiment 1). The result was not due to the speeded identification of a correctly colored ipsilesional item, as there was no benefit from having correctly colored objects in different colors (red strawberry + yellow lemon; Experiment 2). There was also no benefit to extinction from presenting the correct colors in the background of each item (Experiment 3). The data suggest that learned color-form binding can reduce extinction even when color is irrelevant for the task. The result is consistent with preattentive binding of color and shape for familiar stimuli.

On the importance of cognitive profiling: A graphical modelling analysis of domain-specific and domain-general deficits after stroke.

Cognitive problems following stroke are typically analysed using either short but relatively uninformative general tests or through detailed but time consuming tests of domain specific deficits (e.g., in language, memory, praxis). Here we present an analysis of neuropsychological deficits detected using a screen designed to fall between other screens by being 'broad' (testing multiple cognitive abilities) but 'shallow' (sampling the abilities briefly, to be time efficient) - the BCoS. Assessment using the Birmingham Cognitive Screen (BCoS) enables the relations between 'domain specific' and 'domain general' cognitive deficits to be evaluated as the test generates an overall cognitive profile for individual patients. We analysed data from 287 patients tested at a sub-acute stage of stroke (<3 months). Graphical modelling techniques were used to investigate the associative structure and conditional independence between deficits within and across the domains sampled by BCoS (attention and executive functions, language, memory, praxis and number processing). The patterns of deficit within each domain conformed to existing cognitive models. However, these within-domain patterns underwent substantial change when the whole dataset was modelled, indicating that domain-specific deficits can only be understood in relation to linked changes in domain-general processes. The data point to the importance of using over-arching cognitive screens, measuring domain-general as well as domain-specific processes, in order to account for neuropsychological deficits after stroke. The paper also highlights the utility of using graphical modelling to understand the relations between cognitive components in complex datasets.

The Oxford Cognitive Screen (OCS): validation of a stroke-specific short cognitive screening tool.

There is currently no existing freely available short screen for cognitive problems that targets stroke survivors specifically. We have developed a short cognitive screen, the Oxford Cognitive Screen (OCS), to be completed in 15-20 min, designed for use with stroke patients. To maximize inclusion, the test is aphasia- and neglect friendly and covers domains of cognition where deficits frequently occur after stroke, including apraxia and unilateral neglect as well as memory, language, executive function, and number abilities. Domain-specific scores are returned to help direct rehabilitation. This article presents the normative data in a large sample of 140 neurologically healthy participants, a report on incidences of impairments in a sample of 208 acute stroke patients (within 3 weeks of stroke onset), measures of test-retest reliability on an alternate form and convergent and divergent validity. In addition, the full test materials are made freely available for clinical use.

The BCoS cognitive profile screen: Utility and predictive value for stroke.

OBJECTIVE: We examined the utility of the Birmingham Cognitive Screen (BCoS) in discriminating cognitive profiles and recovery of function across stroke survivors. BCoS was designed for stroke-specific problems across 5 cognitive domains: (a) controlled and spatial attention, (b) language, (c) memory, (d) number processing, and (e) praxis. METHOD: On the basis of specific inclusion criteria, this cross-section observational study analyzed cognitive profiles of 657 subacute stroke patients, 331 of them reassessed at 9 months. Impairments on 32 measures were evaluated by comparison with 100 matched healthy controls. Measures of affect, apathy, and activities of daily living were also taken. Between-subjects group comparisons of mean performance scores and impairment rates and within-subject examination of impairment rates over time were conducted. Logistic regressions and general linear modeling were used for multivariate analysis of domain-level effects on outcomes. RESULTS: Individuals with repeated stroke experienced significantly less cognitive recovery at 9 months than those with a first stroke despite similar initial level of cognitive performance. Individuals with left hemisphere lesions performed more poorly than those with right hemisphere lesions, but both groups showed similar extent of recovery at 9 months. BCoS also revealed lesion-side-specific deficits and common areas of persistent problems. Functional outcome at 9 months correlated with domain-level deficits in controlled attention, spatial attention, and praxis over and above initial dependency and concurrent levels of affect and apathy. CONCLUSION: The study demonstrates how BCoS can identify differential cognitive profiles across patient groups. This can potentially help predict outcomes and inform rehabilitation.

Hierarchical processing in Balint's syndrome: a failure of flexible top-down attention.

Patients with Balint' s syndrome are typically impaired at perceiving multiple objects simultaneously, and at evaluating the relationship between multiple objects in a scene (simultanagnosia). These deficits may not only be observed in complex scenes, but also when local elements of individual objects must be integrated into a perceptual global whole. Thus, unlike normal observers, patients with simultanagnosia typically show a bias towards the local forms, even to the extent that they cannot identify the global stimuli. However, we have previously shown that global processing is still attainable in Balint patients in certain scenarios (e.g., when local elements are unfamiliar). This suggests that in addition to a possible perceptual deficit that favors the local elements in these patients, impaired attentional control may be at the core of their unique performance. To test this hypothesis we manipulated the perceptual saliency of the local and global elements in a compound letter task so that it included global-more-salient or local-more-salient displays. We show that a Balint patient was able to accurately identify both global and local targets as long as they were the salient aspect of the compound letter. However, substantial impairment was evident when either the global or local elements were the less salient aspect of the compound letter. We conclude that in Balint' s syndrome there is a failure of flexible top-down attention both in biasing attention away from salient irrelevant aspects of the display (salience-based-selection) and in impaired disengagement from irrelevant but salient items once they have been selected.

Motor extinction: a deficit of attention or intention?

Motor extinction refers to a deficit of motor production on the side opposite a brain lesion that either only becomes apparent or disproportionately worsens during bilateral motor activity. It may arise due either to a contralesional deficit in setting the motor activation level (an intentional deficit) or a deficit in contralesional awareness of the sensory consequences of movement (an attentional deficit). In this study, we investigate the nature of motor extinction in a patient (LR) with a right fronto-temporal lesion through the kinematic analysis of unimanual and bimanual circle-drawing movements. While the ipsi- and contralesional limbs performed comparably for unimanual movements, the contralesional limb demonstrated marked bradykinesia and hypometria during bimanual movements. Furthermore, these deficits were not overcome when visual feedback of the contralesional limb was provided (Experiment 1). However, when performing bimanual movements in the presence of a visual template (Experiment 2), LR was able to overcome the contralesional hypometria but not the bradykinesia which proved intractable across both experiments. Both the bradykinesia and hypometria could result from an intentional deficit of motor production. However, in Experiment 2, LR also demonstrated an abnormal level of positional drift in the contralesional limb for bimanual movements indicative of an additional attentional deficit. We conclude that LR's presentation of motor extinction is the result of a primary intentional deficit and a secondary attentional deficit.

Attending to the possibilities of action.

Actions taking place in the environment are critical for our survival. We review evidence on attention to action, drawing on sets of converging evidence from neuropsychological patients through to studies of the time course and neural locus of action-based cueing of attention in normal observers. We show that the presence of action relations between stimuli helps reduce visual extinction in patients with limited attention to the contralesional side of space, while the first saccades made by normal observers and early perceptual and attentional responses measured using electroencephalography/event-related potentials are modulated by preparation of action and by seeing objects being grasped correctly or incorrectly for action. With both normal observers and patients, there is evidence for two components to these effects based on both visual perceptual and motor-based responses. While the perceptual responses reflect factors such as the visual familiarity of the action-related information, the motor response component is determined by factors such as the alignment of the objects with the observer's effectors and not by the visual familiarity of the stimuli. In addition to this, we suggest that action relations between stimuli can be coded pre-attentively, in the absence of attention to the stimulus, and action relations cue perceptual and motor responses rapidly and automatically. At present, formal theories of visual attention are not set up to account for these action-related effects; we suggest ways that theories could be expected to enable action effects to be incorporated.

Reference frames in visual selection.

We review neuropsychological evidence for visual selection operating in different reference frames. There is general agreement that there may be a separation of coding space near to and farther from the body, and that deficits in selecting stimuli within each form of spatial representation may be impaired in patients with unilateral neglect. However, there remains a lack of consensus about whether all forms of spatial representation relate to the body or whether there are spatial representations based on reference frames abstracted from the body (allocentric and object-centered spatial codes). Here we will review the evidence for spatial coding in these more abstracted reference frames (allocentric and object-centered but also environmental) and argue for the psychological reality of (at least) allocentric spatial coding. We discuss computational accounts of how such codes may be created as objects are selected.

The attraction of yellow corn: reduced attentional constraints on coding learned conjunctive relations.

Physiological evidence indicates that different visual features are computed quasi-independently. The subsequent step of binding features, to generate coherent perception, is typically considered a major rate-limiting process, confined to one location at a time and taking 25 ms per item or longer (A. Treisman & S. Gormican, 1988, Feature analysis in early vision: Evidence from search asymmetries, Psychological Review, Vol. 95, pp. 15-48). We examined whether these processing limitations remain once bindings are learned for familiar objects. Participants searched for objects that could appear either in familiar or unfamiliar colors. Objects in familiar colors were detected efficiently at rates consistent with simultaneous binding across multiple stimuli. Processing limitations were evident for objects in unfamiliar colors. The advantage for the learned color for known targets was eliminated when participants searched for geometric shapes carrying the object colors and when the colors fell in local background areas around the shapes. The effect occurred irrespective of whether the nontargets had familiar colors, but was largest when nontargets had incorrect colors. The efficient search for targets in familiar colors held, even when the search was biased to favor objects in unfamiliar colors. The data indicate that learned bindings can be computed with minimal attentional limitations, consistent with the direct activation of learned conjunctive representations in vision.

The central role of the temporo-parietal junction and the superior longitudinal fasciculus in supporting multi-item competition: evidence from lesion-symptom mapping of extinction.

The present study examined the relations between the lesions linked to visual and tactile extinction (VE and TE), and those related to visual field defects and spatial neglect. Continuous variations in patients' performance were used to assess the link between behavioural scores and integrity of both grey and white matter (GM and WM). We found both common and distinct neural substrates associated with extinction and neglect. Damage to angular and middle occipital gyri, superior temporal sulcus (STS) and insula were linked to VE. Lesions involving the supramarginal gyrus (SMG), intraparietal sulcus, middle frontal and superior temporal gyri (MFG and STG) were associated exclusively with spatial neglect. Lesions affecting the temporo-parietal junction (TPJ), the middle temporal region, middle frontal area (BA46) as well as the insula and putamen were linked to both spatial neglect and VE. Analysis of the relations between VE and TE highlighted the TPJ as the common site for both modalities. These findings suggest that the TPJ plays a general role in identifying salient events in the sensory environment across multiple modalities. Furthermore, WM analyses pointed to superior longitudinal fasciculus (SLF) as critical for interconnecting components of the visuospatial attention network. We demonstrated that functional disconnections resulting from SLF damage contribute to altered performance on attention tasks measuring not only neglect but also VE and TE. We propose that the SLF supports interactions between functionally specialized regions involved in attentional control across multiple sensory modalities.

Systematic assessment of apraxia and functional predictions from the Birmingham Cognitive Screen.

OBJECTIVE: The validity and functional predictive values of the apraxia tests in the Birmingham Cognitive Screen (BCoS) were evaluated. BCoS was developed to identify patients with different forms of praxic deficit using procedures designed to be inclusive for patients with aphasia and/or spatial neglect. METHOD: Observational studies were conducted from a university neuropsychological assessment centre and from acute and rehabilitation stroke care hospitals throughout an English region. Volunteers from referred patients with chronic acquired brain injuries, a consecutive hospital sample of patients within 3 months of stroke (n=635) and a population based healthy control sample (n=100) were recruited. The main outcome measures used were the Barthel Index, the Nottingham Extended Activities of Daily Living Scale as well as recovery from apraxia. RESULTS: There were high inter-rater reliabilities and correlations between the BCoS apraxia tasks and counterpart tests from the literature. The vast majority (88.3%) of the stroke survivors were able to complete the screen. Pantomime and gesture recognition tasks were more sensitive in differentiating between individuals with left hemisphere damage and right hemisphere damage whereas the Multistep Object Use test and the imitation task had higher functional correlates over and above effects of hemiplegia. Together, the initial scores of the four tasks enabled predictions with 75% accuracy, the recovery of apraxia and independence level at 9 months. CONCLUSIONS: As a model based assessment, BCoS offers a quick and valid way to detect apraxia and predict functional recovery. It enables early and informative assessment of most stroke patients for rehabilitation planning.

When connectedness increases hemispatial neglect.

Patients with left neglect were tested with "chimeric" figures composed of the right and left halves of two different objects. The connectivity relation was modulated between the two half figures. For some displays, the two chimeric halves were separated by a small gap, while in others, the separate halves were connected by a line segment. In line with previous reports, performance on reporting the left half improved when the chimera were separated; but when a line connected the two separated halves the advantage was lost. If the connecting line was broken, the performance was again enhanced. The results suggest an important role for connectedness in the representation of perceptual objects and in the distribution of attention in neglect.

Modulating wheelchair navigation in patients with spatial neglect.

Patients who have had a stroke resulting in the deficit of visuo-spatial neglect are normally not provided with a powered wheelchair, as they are either considered or found to be unsafe navigating about their environment. As these patients are relatively unlikely to regain functional mobility by walking, the denial of alternative forms of mobility is of particular concern. Modest progress has been made over the past two decades with regards to the rehabilitation of neglect but there have been calls for further research which addresses "real world" measures of independence such as wheelchair navigation. In this study, we investigated the ability of patients with neglect to improve their performance when navigating a powered wheelchair by using theoretically-driven strategies that have shown promise in previous studies (spatial cueing and limb activation). Strategies were applied and tested in the most realistic and practical manner for each individual, based on their abilities and concurrent deficits. Performance was improved by the experimental strategies. The data suggest it is possible to apply theoretically-driven strategies to improve wheelchair navigation in patients with neglect and are supportive of further studies that could lead to improved access to powered mobility by this population in the future.

The grouping benefit in extinction: overcoming the temporal order bias.

Grouping between contra- and ipsilesional stimuli can alleviate the lateralised bias in spatial extinction (Gilchrist, Humphreys, & Riddoch, 1996; Ward, Goodrich, & Driver, 1994). In the current study we demonstrate for the first time that perceptual grouping can also modulate the spatio/temporal biases in temporal order judgements affecting the temporal as well as the spatial coding of stimuli. Perceived temporal order was assessed by presenting two coloured letter stimuli in either hemi-field temporally segregated by a range of onset-intervals. Items were either identical (grouping condition) or differed in both shape and colour (non-grouping condition). Observers were required to indicate which item appeared second. Patients with visual extinction had a bias against the contralesional item appearing first, but this was modulated by perceptual grouping. When both items were identical in shape and colour the temporal bias against reporting the contralesional item was reduced. The results suggest that grouping can alter the coding of temporal relations between stimuli.

Functional relations trump implied motion in recovery from extinction: evidence from the effects of animacy on extinction.

Patients with extinction show a characteristic impairment in the identification of objects when two items are presented simultaneously, typically reporting the ipsilesional item only. The effect is thought to be due to a spatial bias advantaging the ipsilesional item under conditions of competing concurrent stimulation. Action relations between objects can result in recovery from extinction as the object pair may be perceived as a single group rather than competing perceptual units. However, objects interacting together can also have implied motion. Here we test whether implied motion is necessary to generate recovery from extinction. We varied orthogonally whether animate and inanimate objects were paired together in positions related or unrelated to action. Implied motion was greater when an animate object was present than when both stimuli were inanimate. Despite this, recovery from extinction was greater when actions were shown between inanimate objects. We suggest that actions between inanimate objects are perceived more easily due to the surfaces of these stimuli being designed for functional goals (e.g., the flat surface of a hammer head is designed to hit the flattened head of a nail). Attention is sensitive to the fit between potential action and the functional properties of objects, and not just to implied motion between stimuli.

The paired-object affordance effect.

We demonstrate that right-handed participants make speeded classification responses to pairs of objects that appear in standard co-locations for right-handed actions relative to when they appear in reflected locations. These effects are greater when participants "weight" information for action when deciding if 2 objects are typically used together, compared with deciding if objects typically occur in a given context. The effects are enhanced, and affect both types of decision, when an agent is shown holding the objects. However, the effects are eliminated when the objects are not viewed from the first-person perspective and when words are presented rather than objects. The data suggest that (a) participants are sensitive to whether objects are positioned correctly for their own actions, (b) the position information is coded within an egocentric reference frame, (c) the critical representation involved is visual and not semantic, and (d) the effects are enhanced by a sense of agency. The results can be interpreted within a dual-route framework for action retrieval in which a direct visual route is influenced by affordances for action.

Neuropsychological evidence for visual- and motor-based affordance: effects of reference frame and object-hand congruence.

Two experiments are reported that use patients with visual extinction to examine how visual attention is influenced by action information in images. In Experiment 1 patients saw images of objects that were either correctly or incorrectly colocated for action, with the objects held by hands that were congruent or incongruent with those used premorbidly by the patients. The images were also shown from a 1st- and 3rd-person perspective. There was an overall reduction in extinction for objects colocated for action. In addition, there was an extra benefit when the objects were held in hands congruent with those used by the patients and when the objects were seen from a 1st-person perspective. This last result fits with an effect of motor simulation, over and above a purely visual effect based on positioning objects correctly for action. Experiment 2 showed that effects of hand congruence could emerge with images depicted from a 3rd-person perspective when patients saw themselves holding the objects. The data indicate 2 effects of action information on extinction: (a) an effect of colocating objects for action, which does not depend on a self-reference frame (a visual effect), and (b) an effect sensitive to object-hand congruence, which does depend on a self-reference frame (a motor-based effect). The self-reference frame is induced when stimuli are viewed from a 1st-person perspective and when an image of the self is seen from a 3rd-person perspective. Both visual and motor-based effects of action information facilitate the spread of attention across objects.