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Biomedical subjects

I H Robertson

Publications and source records attributed to I H Robertson.

At least 19 recordsLinked to original sources
PubMed2001

The role of perceptual load in neglect: rejection of ipsilesional distractors is facilitated with higher central load.

Neglect is known to produce a bias towards the ipsilesional side. Here we examined whether this bias is automatic or can be modulated by manipulating perceptual load in a relevant task [e.g., Lavie, N. (1995). Perceptual load as a necessary condition for selective attention. Journal of Experimental Psychology: Human Perception and Performance, 21, 451-468]. Three patients with left neglect and three healthy controls made speeded choice responses to a target letter in the center of the display while attempting to ignore an irrelevant distractor presented on left or right. Perceptual load was manipulated by inducing a search for the target that appeared with another central stimulus, which was either a blob (low load) or a nontarget letter (higher load). Response competition effects from ipsilesional distractors were significantly reduced by higher load. The same increase of load, however, did not decrease distractor effects in the control group, as expected [e.g., Lavie, N., & Cox, S. (1997). On the efficiency of attentional selection: Efficient visual search results in inefficient rejection of distraction. Psychological Science, 8, 395-398]. These results demonstrate that ipsilesional bias in neglect is not fully automated and emphasize an additional restriction of perceptual capacity. Moreover, they supported our prediction that reduced perceptual capacity in neglect can lead to improved distractor rejection with just small increases in perceptual load.

Aged↗
PubMed2001

Do we need the "lateral" in unilateral neglect? Spatially nonselective attention deficits in unilateral neglect and their implications for rehabilitation.

This paper reviews evidence that the spatial imbalance of attention by which unilateral neglect is often defined is a necessary but not sufficient factor in the persistence of this disorder. A second, nonspatially lateralized loss of attentional capacity is required to coexist with the spatial bias for the disorder to persist in a clinically significant way, it is argued. To this end, I first review evidence from visual and auditory attention studies to show that unilateral neglect is very strongly associated with a fundamental loss of attentional capacity that is not confined to one region of space. Second, I attempt to characterize the nature of this attentional capacity in relation in particular to functional brain imaging studies of attention. Third, I demonstrate that the spatial imbalance in neglect can be reduced by manipulations of the nonlateralized attentional capacity and finish by reviewing the rehabilitation implications of these manipulations.

Attention↗
PubMed2001

Interaction of hand use and spatial selective attention in children.

It has been argued that concurrent motor action can modulate visual spatial attention. The visual spatial biases of adult patients with unilateral neglect, for example, can be ameliorated by simultaneous use of the contralesional hand. Such improvements are most dramatic when the contralesional hand is moved within contralesional space. To date, evidence of such an interaction in neurologically healthy individuals has not been presented. Line bisection is a simple task that is sensitive to attentional spatial bias. When young children are asked to bisect horizontal lines using their right hands, they show a reliable, if small, bias that is consistent with the pattern seen in adult neglect. This bias is reversed when the left hand is used. Here, we show that these effects are significantly modulated by the location of the movements relative to the body mid-line - specifically that the conjunction of hand movements within ipsilateral space is necessary for the previously reported pattern to be observed. We further demonstrate that these effects are not present in the bisections of neurologically healthy adults. In a final study, we examined whether the hand movement effects seen in children's line bisections would persist in a purely visual task (that is when the movements were made irrelevant to the response). Again, significant modulation of children's perception by concurrent hand movements - and the relative location of those movements - was observed. The theoretical and clinical implications of the results are discussed.

Attention↗
PubMed2001

Effects of attention and unilateral neglect on auditory stream segregation.

Two pairs of experiments studied the effects of attention and of unilateral neglect on auditory streaming. The first pair showed that the build up of auditory streaming in normal participants is greatly reduced or absent when they attend to a competing task in the contralateral ear. It was concluded that the effective build up of streaming depends on attention. The second pair showed that patients with an attentional deficit toward the left side of space (unilateral neglect) show less stream segregation of tone sequences presented to their left than to their right ears. Streaming in their right ears was similar to that for stimuli presented to either ear of healthy and of brain-damaged controls, who showed no across-ear asymmetry. This result is consistent with an effect of attention on streaming, constrains the neural sites involved, and reveals a qualitative difference between the perception of left- and right-sided sounds by neglect patients.

Aged↗
PubMed2001

Characterising phantom limb phenomena in upper limb amputees.

A systematic descriptive survey was carried out on a clinic population with acquired upper limb amputation in which clear distinctions were made between phantom experiences, pre-amputation pain and stump pain. It was found that of 76 participants 96% reported phantom experiences and 84% were currently experiencing phantom limb phenomena (PLP). Sixty-nine percent (69%) of those currently experiencing phantom phenomena stated that the phantoms were painful. Significant relationships were found between frequency of phantom experiences and side and level of amputation. In addition, the presence of 'trigger' points reported by a sub group of participants was found to be associated with the frequency of phantoms and painful phantoms. This finding could provide support for cortical reorganisation post amputation. It is suggested that detailed individual 'profiling' of phantom experiences is important and would have the following implications: it would contribute to existing knowledge and provide new insights into the central nervous system's reorganisation post-amputation; it would provide an accurate way of representing amputees' anomalous perceptions; it would alert health professionals to the presence, variety and extent of PLP following amputation.

Adolescent↗
PubMed2001

The differential assessment of children's attention: the Test of Everyday Attention for Children (TEA-Ch), normative sample and ADHD performance.

"Attention" is not a unitary brain process. Evidence from adult studies indicates that distinct neuroanatomical networks perform specific attentional operations and that these are vulnerable to selective damage. Accordingly, characterising attentional disorders requires the use of a variety of tasks that differentially challenge these systems. Here we describe a novel battery, the Test of Everyday Attention for Children (TEA-Ch), comprising nine subtests adapted from the adult literature. The performance of 293 healthy children between the ages of 6 and 16 is described together with the relationships to IQ, existing measures of attention, and scholastic attainment. This large normative sample also allows us to test the fit of the adult model of functionally separable attention systems to the observed patterns of variance in children's performance. A Structural Equation Modelling approach supports this view. A three-factor model of sustained and selective attention and higher-level "executive" control formed a good fit to the data, even in the youngest children. A single factor model was rejected. There are behavioural and anatomical grounds to believe that Attention Deficit Disorder (ADD) is particularly associated with poor self-sustained attention and behavioural control. The TEA-Ch performance of 24 boys diagnosed with ADD presented here is consistent with this view. When performance levels on WISC-III subtests were taken into account, specific deficits in sustained attention were apparent while selective attention performance was within the normal range.

Activities of Daily Living↗
PubMed2000

Improving the clinical diagnosis of personal neglect: a reformulated comb and razor test.

Beschin and Robertson (1997) devised a simple clinical test of left personal neglect, which characterises personal grooming behaviour according to the proportion of the total activity that is directed to the left side of the body. Although this test proved highly reliable, and more sensitive than prior diagnostic techniques, its formulation may yet be improved. The present paper reports a reanalysis of Beschin and Robertson's (1997) data, using additional control subjects, and a formula which characterises personal neglect as a lateral bias of behaviour rather than as a lateralised deficit. It is shown that this formula greatly enhances the test's sensitivity to the behavioural abnormalities of brain damaged patients, and it is recommended that this modification be adopted for the future diagnosis of personal neglect.

Aged↗
PubMed2000

The automatic updating of egocentric spatial relationships and its impairment due to right posterior cortical lesions.

The non-visual updating of body-centred spatial relationships was investigated in an experiment in which blindfolded patients had to point to previously seen targets after a body rotation in the absence of vision. Patients with lesions to the right dorsal (RD) area were impaired at updating their positions relative to non-RD patients and normal subjects: they tended to underestimate systematically the angle through which they had turned. The results are interpreted in terms of impoverished locomotor input and/or systematically biased processing or locomotor proprioception in the RD patients, which prevented accurate tracking of changes in egocentric spatial relationships.

Adult↗
PubMed2000

Rehabilitation of executive functioning: an experimental-clinical validation of goal management training.

Two studies assessed the effects of a training procedure (Goal Management Training, GMT), derived from Duncan's theory of goal neglect, on disorganized behavior following TBI. In Study 1, patients with traumatic brain injury (TBI) were randomly assigned to brief trials of GMT or motor skills training. GMT, but not motor skills training, was associated with significant gains on everyday paper-and-pencil tasks designed to mimic tasks that are problematic for patients with goal neglect. In Study 2, GMT was applied in a postencephalitic patient seeking to improve her meal-preparation abilities. Both naturalistic observation and self-report measures revealed improved meal preparation performance following GMT. These studies provide both experimental and clinical support for the efficacy of GMT toward the treatment of executive functioning deficits that compromise independence in patients with brain damage.

Adult↗
PubMed2000

Neglect between but not within auditory objects.

Unilateral neglect is frequently characterized by the presence of extinction, which is a lack of awareness to contralesional visual stimuli in the presence of those further towards the ipsilesional side. It has been established that this visual extinction can be reduced if the stimuli are grouped together into a single object. However, attention between and within auditory objects has never before been studied. We demonstrate for the first time that unilateral neglect--hitherto thought primarily to be a disorder of visuospatial processing-- involves a specific deficit in allocating attention between auditory objects separated only in time and not in space. Importantly, this deficit is restricted to comparisons between sounds: the patients' ability to make within-sound comparisons is similar to that of controls. These differences cannot be explained in terms of different time spans over which comparisons must be made. The results suggest unilateral neglect is linked to--if not actually determined by--a reduction in attentional capacity in both the visual and auditory domains, and across the dimensions of both space and time. The findings have potential clinical applications.

Acoustic Stimulation↗
PubMed1999

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↗
PubMed1999

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↗
PubMed1999

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↗
PubMed1999

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↗
PubMed1999

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↗