Compensations for brain deficits. "Every cloud...".
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Brain↗
Biomedical subjects
I H Robertson
Publications and source records attributed to I H Robertson.
When a rubber hand 'feels' what the real hand cannot.
We examined a patient who was clinically much better at reporting tactile stimulation when he could see his stimulated hand. Experimentally, we found that he had difficulty detecting taps accompanied by a salient (but not predictive) light located directly above his concealed hand. However, his performance was dramatically improved if the light was attached to a rubber hand situated in line with the patient's hidden hand. Previous studies have suggested that tactile sensitivity can be improved by nearby visual stimulation. However, our effect shows that crossmodal sensory facilitation does not only depend upon simple spatial proximity alone. Rather, a simultaneous visual event dramatically improves perception of touch specifically when it is attributed to the perceiver's stimulated limb.
Functional Laterality↗
The absent mind: further investigations of sustained attention to response.
We have previously demonstrated that performance on a brief and conceptually simple laboratory task (the Sustained Attention to Response Test: SART) was predictive of everyday attentional failures and action slips in brain injured patients and normal control participants. The SART is a go-no-go paradigm in which the no-go target appears rarely and unpredictably. Performance on this measure was previously interpreted as requiring sustained attention to response rather than a putative 'response inhibition' capacity. Three further studies are presented which support this claim. They demonstrate that performance is crucially determined by the duration of time over which attention must be maintained on one's own actions that this demand underpins the task's relationship to everyday attentional lapses. In keeping with a number of recent studies it suggests that inefficiencies in the maintenance of attentional control may be apparent over much briefer periods than is traditionally considered using vigilance measures and analysis.
Activities of Daily Living↗
Divided attention impairments after traumatic brain injury.
This research investigated whether people with severe traumatic brain injury (TBI) are impaired on divided attention tasks requiring working memory. In experiment 1, a severe TBI and control group performed two tasks requiring working memory separately and concurrently. Results showed that the TBI group had impaired divided attention when performing the two tasks concurrently, although the two groups did not differ in performance when these tasks were performed separately. Experiment 2 showed that performance on the paced auditory serial addition task improved with increases in the intertrial interval for both TBI and control groups. A meta-analysis showed that TBIs are impaired on divided attention when the tasks require controlled processing, but not when the tasks can be carried out relatively automatically.
Attention↗
Rehabilitation of brain damage: brain plasticity and principles of guided recovery.
Rehabilitation of the damaged brain can foster reconnection of damaged neural circuits; Hebbian learning mechanisms play an important part in this. The authors propose a triage of post-lesion states, depending on the loss of connectivity in particular circuits. A small loss of connectivity will tend to lead to autonomous recovery, whereas a major loss of connectivity will lead to permanent loss of function; for such individuals, a compensatory approach to recovery is required. The third group have potentially rescuable lesioned circuits, but guided recovery depends on providing precisely targeted bottom-up and top-down inputs, maintaining adequate levels of arousal, and avoiding activation of competitor circuits that may suppress activity in target circuits. Empirical data are implemented in a neural network model, and clinical recommendations for the practice of rehabilitation following brain damage are made.
Association Learning↗
Setting goals for cognitive rehabilitation.
Evidence for experience-dependent plasticity of the brain, including cell regeneration, means that rehabilitation can aim at reinstituting impaired cognitive function, as well as at training compensatory strategies for the lost function. New theoretical frameworks make predictions regarding the circumstances under which these two approaches should each be attempted. There has been progress over the past 6 years in designing effective rehabilitation strategies, with more of these having a strong theoretical basis in cognitive neuroscience. Basic cognitive science has generated counter-intuitive, but effective cognitive rehabilitation methods, showing that the goal of rehabilitation need not always be the most obvious one dictated by real life performance. Limb Activation Training for unilateral neglect is an example of a theoretically derived cognitive rehabilitation procedure that has now been clinically evaluated in clinical trials.
Brain Injuries↗
Phasic alerting of neglect patients overcomes their spatial deficit in visual awareness.
Patients with extensive damage to the right hemisphere of their brain often exhibit unilateral neglect of the left side of space. The spatial attention of these patients is strongly biased towards the right, so their awareness of visual events on the left is impaired. Extensive right-hemisphere lesions also impair tonic alertness (the ability to maintain arousal). This nonspatial deficit in alertness is often considered to be a different problem from spatial neglect, but the two impairments may be linked. If so, then phasically increasing the patients' alertness should temporarily ameliorate their spatial bias in awareness. Here we provide evidence to support this theory. Right-hemisphere-neglect patients judged whether a visual event on the left preceded or followed a comparable event on the right. They became aware of left events half a second later than right events on average. This spatial imbalance in the time course of visual awareness was corrected when a warning sound alerted the patients phasically. Even a warning sound on the right accelerated the perception of left visual events in this way. Nonspatial phasic alerting can thus overcome disabling spatial biases in perceptual awareness after brain injury.
Acoustic Stimulation↗
Visual attention: controlling what we see and do.
Controlling what we see and do in complex environments depends upon the interaction of top-down control mechanisms located in the prefrontal cortex, on the one hand, and bottom-up competition between objects for limited perceptual resources in posterior cortical areas, on the other.
Attention↗
Atrial fibrillation and cognitive function: case-control study.
Atrial fibrillation is an important and independent risk factor for cerebrovascular disease and vascular dementia. There is increasing evidence that atrial fibrillation is associated with an increased risk of asymptomatic or silent cerebral infarction and as a result may confer an increased risk of progressive cognitive impairment on a person. In this study we sought to determine whether this hypothesis could be explored in a prospective case controlled design. Twenty seven patients with non-valvular atrial fibrillation (NVAF) and no history of stroke, transient ischaemic attack, dementia, and thyrotoxicosis were compared with 54 age and sex matched controls in sinus rhythm. All cases underwent clinical examination, ECG, and psychological assessment using a battery of nine neuropsychological tests. Between group analysis and a comparison of mean test scores of paired controls with cases were undertaken. The presence of atrial fibrillation was consistently associated with poorer performances on all the subtests of the neuropsychological battery. There was no association between duration of atrial fibrillation and performance. These results provide evidence to justify further examination of the hypothesis in a larger prospective study to determine whether antithrombotic therapy may protect against cognitive decline in patients at maximal risk of silent cerebral ischaemia and associated cognitive decline.
Aged↗
Personal versus extrapersonal neglect: a group study of their dissociation using a reliable clinical test.
The validation of a simple quantitative clinical test of personal neglect is described in this study of 17 right brain damaged CVA patients with extrapersonal neglect, 14 without unilateral extrapersonal neglect, 13 left brain damaged CVA patients and 17 age-matched controls. The test had a high reliability and clearly differentiated neglect patients from all other groups. Furthermore the test identified a much higher incidence of personal neglect among extrapersonal neglect patients (59%) than has previously been found. Moreover this study confirms earlier findings by showing a double dissociation between personal and extrapersonal neglect. Seven patients with extrapersonal neglect showed no personal neglect while five patients showing no extrapersonal neglect did show personal neglect on this test.
Activities of Daily Living↗
Attentional competition between modalities: extinction between touch and vision after right hemisphere damage.
The phenomenon of extinction, which occurs frequently after unilateral brain damage, involves a failure to detect the more contralesional of two simultaneously presented stimuli, but with preserved detection of single ipsilesional or contralesional stimuli. Current accounts suggest that the disorder reflects a bias of selective attention, in which ipsilesional stimuli have a competitive advantage. Extinction may be manifested within any one of the major sensory modalities (vision, audition, touch), or it may occur within several modalities in a given individual. Given recent evidence in normals for attentional links between separate sensory modalities, we examined whether extinction can also occur cross-modally, i.e. for double-simultaneous stimuli in separate sensory modalities. We tested whether an ipsilesional event sufficient to extinguish a contralesional stimulus within the same modality may also extinguish a contralesional stimulus in a different modality. Our three patients had right hemisphere damage, and reliable within-modality extinction for visual and tactile stimuli. They also showed significant cross-modal extinction, such that an ipsilesional tactile (or visual) event extinguished awareness of a simultaneous visual (or tactile) event on the contralesional side. These results, which provide the first quantitative evidence for cross-modal extinction, were replicated in a second experiment in which visual and tactile stimuli in the cross-modal conditions were presented at non-homologous elevations within each hemispace. We conclude that after unilateral damage, ipsilesional stimuli have a competitive advantage over contralesional stimuli, and that this affects competition between stimuli from different modalities as well as stimuli within the same modality. These findings are consistent with recent evidence for competitive interactions between tactile and visual events in the control of spatial attention in normals.
Adult↗
'Oops!': performance correlates of everyday attentional failures in traumatic brain injured and normal subjects.
Insufficient attention to tasks can result in slips of action as automatic, unintended action sequences are triggered inappropriately. Such slips arise in part from deficits in sustained attention, which are particularly likely to happen following frontal lobe and white matter damage in traumatic brain injury (TBI). We present a reliable laboratory paradigm that elicits such slips of action and demonstrates high correlations between the severity of brain damage and relative-reported everyday attention failures in a group of 34 TBI patients. We also demonstrate significant correlations between self- and informant-reported everyday attentional failures and performance on this paradigm in a group of 75 normal controls. The paradigm (the Sustained Attention to Response Task-SART) involves the withholding of key presses to rare (one in nine) targets. Performance on the SART correlates significantly with performance on tests of sustained attention, but not other types of attention, supporting the view that this is indeed a measure of sustained attention. We also show that errors (false presses) on the SART can be predicted by a significant shortening of reaction times in the immediately preceding responses, supporting the view that these errors are a result of 'drift' of controlled processing into automatic responding consequent on impaired sustained attention to task. We also report a highly significant correlation of -0.58 between SART performance and Glasgow Coma Scale Scores in the TBI group.
Activities of Daily Living↗
Auditory sustained attention is a marker of unilateral spatial neglect.
The relationships between performance on a non-spatially-lateralized measure of sustained attention and spatial bias on tests sensitive to unilateral neglect were considered in a group of 44 patients with right hemisphere lesions following stroke. As predicted from earlier studies showing a strong association between unilateral spatial neglect and sustained attention, performance on a brief and monotonous tone-counting measure formed a significant predictor of spatial bias across a variety of measures of unilateral visual neglect. This study provides further evidence for a very close link between two attentional systems hitherto regarded as being quite separate, namely a spatial attention system implicated in unilateral neglect and a sustained attention system. A close connection between these two systems was predicted by Posner, who argued that the right hemisphere-dominant sustained attention system provides a strong modulatory influence on the functioning of the lateralized posterior attention system.
Acoustic Stimulation↗
Believing what you feel: using proprioceptive feedback to reduce unilateral neglect.
Unilateral spatial neglect declines when participants reach to grip the center of long metal rods compared with when they point to the perceived center, suggesting that visuomotor control systems are less affected by neglect than other representational systems (I. H. Robertson, D. Nico, & B. Hood, 1995). In this study, 16 participants with unilateral left neglect actually picked up rods, and we predicted short-term improvements in neglect because of induced conflict between a phenomenally symmetrical visual world on the one hand and a proprioceptively conveyed rightward-biased world on the other. With participants serving as their own controls, significant short-term improvements in neglect were found on 2 out of 4 neglect tasks after participants experienced proprioceptive feedback discrepant from the judgments they made on the basis of visual information alone.
Aged↗
Motor recovery after stroke depends on intact sustained attention: a 2-year follow-up study.
The functional recovery of 47 right-brain-damaged stroke patients was studied over a 2-year period. The researchers hypothesized that sustained attention capacity should predict the degree of motor and functional recovery over this period because of a proposed privileged role of sustained attention in learning-based recovery of function. As predicted, significant correlations were found between sustained attention capacity at 2 months and functional status (including the Barthel Index) at 2 years. This relationship was shown to exist independently of 2-month functional status. Furthermore, compared with a left-brain-damaged group of cerebrovascular accident (CVA) patients, the right-brain CVA group did not recover functional ability as well over the 2-year period. This increasing difference in functional status over a 2-year period was mirrored by an emerging difference in sustained attention capacity, in favor of the left-brain CVA group.
Aged↗
Assessing the reliability and abnormality of subtest differences on the Test of Everyday Attention.
OBJECTIVES: To assist clinicians with the analysis of an individual's profile of subtest strength and weaknesses on the Test of Everyday Attention (TEA). DESIGN: The study applied psychometric methods for the quantitive analysis of subtest profiles (Silverstein, 1982, 1984a, b). METHODS: Formulae to compute the standard error of the difference and standard deviation of the difference between a subtest and a client's mean subtest scores were applied to determine critical values for reliable and abnormal differences. The data used were derived from the TEA standardization sample (N = 154). RESULTS: Tables for examining whether an individual's TEA subtest profile contains reliable and abnormal subtest discrepancies are presented. CONCLUSIONS: Elegant methods of analysing a subtest profile were extended for use with the Test of Everyday Attention. In keeping with the rationale underlying the measurement of neuropsychological deficit (Lezak, 1995), these methods complement the existing TEA normative comparison standards by providing individual comparison standards for a client's performance. Guidance on the use of the tables is offered; the distinction between reliable and abnormal differences is highlighted.
Adult↗
The structure of normal human attention: The Test of Everyday Attention.
A range of tests of everyday attention is described, based on ecologically plausible activities such as searching maps, looking through telephone directories, and listening to lottery number broadcasts. An age-, sex- and IQ-stratified sample of 154 normal participants was given these tests, along with a number of existing tests of attention. The factor structure revealed by this data set matched well contemporary evidence for a set of functionally independent attentional circuits in the brain, and included factors for sustained attention, selective attention, attentional switching and auditory-verbal working memory. The Test of Everyday Attention (TEA), which was developed and standardized on the basis of these subtests, has three parallel forms, high test-retest reliability, and correlates significantly with existing measures of attention. Furthermore, selected subtests successfully discriminate among a number of brain-impaired groups, including closed head injury versus age-matched controls, minimal versus mild Alzheimer's disease, and progressive supranuclear palsy patients versus age-matched controls.
Activities of Daily Living↗
Late rehabilitation for closed head injury: a follow-up study of patients 1 year from time of discharge.
Subsequent to the setting up of an outpatient psychological service for head-injured patients, 50 patients were interviewed a year from the time of their discharge from our neurorehabilitation unit. The problems which persisted at this stage are presented and discussed. Some of the difficulties encountered in the evaluation of rehabilitation effects are identified. We conclude that: (1) there is a desperate need in the UK for more long-term support and rehabilitation services for this group of patients and (2) it is essential that such services are carefully monitored and evaluated despite the difficulties involved.
Adolescent↗