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PubMed1983

Differential drawing size associated with unilateral brain damage.

Size of Greek Cross reproductions was compared using 35 persons having unilateral right (RHD), 35 having unilateral left (LHD) hemisphere damage and 38 non-neurologic controls. With right hand tapping speed statistically controlled, RHD drawings were significantly larger than LHD reproductions. Spatial Relations scores were significantly associated with drawing size in the RHD group only, following adjustment for right hand tapping speed. Aphasia Screening scores were unrelated to drawing size. These data demonstrate that LHD/RHD drawing size differences are independent of any basic motor impairment and that for RHD subjects, drawing size is positively correlated with visuospatial impairment.

Adult↗
PubMed1985

Information processing deficits in Parkinson's disease during movement.

The capacity to process information during movement selection and execution was studied in Parkinsonian patients and controls in a task involving movement of a hand-held stylus between two targets whose size and separation could be systematicaly varied. Movement time and accuracy were evaluated when the size and required accuracy of movements were changed to modify movement difficulty. Movement time and inaccuracy of patients with Parkinson's disease were exaggerated by increasing target separation so as to increase movement extent (target size held constant) or by decreasing target size (target separation held constant). The fact that these changes in task difficulty caused greater deterioration of performance for patients than for controls is consistent with previous studies indicating that Parkinsonian patients have deficits in executing high-velocity movements. These data also show that performance deficits by Parkinsonian patients can be brought out by increasing movement difficulty through requiring increased movement accuracy. These findings are interpreted in relation to the relative contribution of deficits in movement execution vs motor programming in the motor disorders of Parkinson's disease.

Aged↗
PubMed1990

Individual variation in line bisection: a study of normal subjects with application to the interpretation of visual neglect.

Investigations of left visuo-spatial neglect are reviewed with special reference to line bisection performance. Attention is then drawn to inconsistencies in the direction and magnitude of transection displacements in group studies of normal controls. We argue that the lack of reliable information about normal mechanisms for line bisection makes it impossible to interpret pathological performance in neglect. Accordingly, we report a case-series of 22 normal young adults, each of whom bisects 10 lines of differing lengths 10 times each. There is very substantial between-subject variation in both the magnitude and direction of the linear regression of transection displacement on line length; there are likewise considerable differences in the magnitude of the linear regression of standard deviation on line length. These two sources of individual variation are uncorrelated. We propose a psychophysical theory of line bisection, and suggest that the basic mechanisms responsible for task-performance are qualitatively intact in visuo-spatial neglect, albeit quantitatively impaired.

Adult↗
PubMed1991

Hemispheric activation vs spatio-motor cueing in visual neglect: a case study.

We report a case of mild visuo-spatial neglect consequent upon right-hemisphere stroke. At the time of testing, the patient had a complete left visual field deficit but only a very slight left hemiparesis. Under conventional testing conditions, line bisection performed with the right hand showed more severe left neglect than when performed with the left hand. This pattern of performance could, however, be modified, both quantitatively and qualitatively, by changing the starting position of the patient's hand when bisecting horizontal lines. The results suggest that spatio-motor cueing has a more profound effect upon task performance than does differential hemispheric activation per se. We also provide a demonstration that, in a normal subject, the starting position of the hand is likewise a crucial determinant of task performance. In this case, however, there is also an interaction between the hand (and hence hemisphere) deployed and the position of that hand in space.

Adult↗
PubMed1991

Figural modulation of visuo-spatial neglect: a case study.

We report a case of severe left visuo-spatial neglect consequent upon right-hemisphere stroke. In Experiment 1, horizontal and vertical (radial) line bisection is performed; the patient displays left neglect and "altitudinal" (radial) neglect, placing his transections too far to the right and to the top, respectively. In Experiment 2, the patient is required to place a dot at the centre of squares and circles, the horizontal and vertical extents of which are identical to the length of the lines employed in Experiment 1. Performance is now extremely accurate. In Experiment 3, the height of the rectangular or elliptical figure whose midpoint is to be estimated is held constant whilst length varies. In Experiment 4, the length of the figure is held constant whilst height is varied. Both manipulations exert a profound, lawful influence on the patient's estimate of each figure's midpoint. We provide some preliminary hypotheses concerning how configurational constraints may affect perceptual and attentional processes in visual neglect.

Attention↗
PubMed1992

To halve and to halve not: an analysis of line bisection judgements in normal subjects.

Normal adults were tested in a series of three experiments to examine the influences of spatial location and cueing upon line bisection judgements. Judgements in all three experiments were strongly influenced by cueing with a letter at one or other end of the line. The spatial location of the line (in left, central or right body space) also had a minor effect in Experiments 1 and 2, where evidence was additionally found for a small constant error when lines were presented centrally. It is argued from the results of Experiments 2 and 3, where no explicit bisection response was required, that perceptual/attentional factors, rather than an orienting bias, play the major role in mediating the cueing effect. It is concluded that there is a substantial attentional effect upon judgements of extent, whereby paying less attention decreases perceived relative line length. However the constant error and the effect of spatial location, whilst mainly perceptual in nature, may also be partly determined by premotor orienting biases caused by differential hemispheric activation.

Adult↗
PubMed1993

Cross-modal associations and the human amygdala.

The role of the human amygdala in cross-modal associations was investigated in two subjects: SM-046, who had bilateral damage circumscribed to the amygdala; and the patient known as Boswell, whose damage in both temporal lobes includes the amygdala and surrounding cortices. Neither subject was impaired on Tactile-Visual or Visual-Tactile cross-modal tasks using the Arc-Circle test, suggesting that the amygdala is not involved in cross-modal associations involving perceptually "equivalent" basic stimulus properties. On the other hand, the results are compatible with the amygdala's involvement in higher-order associations between exteroceptive sensory data and interoceptive data concerned with correlated somatic states.

Adult↗
PubMed1994

Parkinson's disease: reorganization of the reach to grasp movement in response to perturbation of the distal motor patterning.

This study assessed the kinematic changes to the reach to grasp movement in response to a perturbation of object size in 15 Parkinson's disease (PD) and 15 control subjects. For non-perturbed trials subjects reached 35 cm to grasp and lift either an illuminated small (0.7 cm) or large (8 cm) diameter cylinder. For perturbed trials (20%), illumination shifted unexpectedly from the small to the large or from the large to the small cylinder at the onset of the reach. For Condition One trials subjects were given no instructions as to which grasp to use. With perturbation, they thus naturally changed grasp from precision grip to whole hand prehension or vice versa. The results for the PD subjects indicated a slowness at the transition from one to another grasp. This contrasted to the smooth transitions when perturbation required only a change of grasp aperture (precision grip--Condition Two; whole hand prehension--Condition Three). PD subjects thus showed dysfunction in the suppression/activation of different grasp programs rather than deficits in the on-line modification of an operating program.

Aged↗
PubMed1994

Impairment of grasping movements following a bilateral posterior parietal lesion.

The observation of a patient (A.T.) with a bilateral posterior parietal lesion of vascular origin is reported. A.T. presented a bilateral (more marked on the right) deficit in grasping simple objects (neutral cylindrical dowels) without deficit in reaching toward the location of these objects. The major symptom was an exaggerated anticipatory opening of the fingers with poor correlation with object size, resulting in awkward grasps. It was present both when the hand was visible to the subject and when it was not. This deficit was much less marked if the neutral objects were replaced by usual objects of the same sizes. Finally, in tasks where she had to indicate with her fingers the size of visual objects presented as virtual images through a mirror, or the size of imagined usual objects, A.T. performed normally. These results are discussed within the framework of a dual representation of objects. Only the "pragmatic" representation for steering object-oriented actions would be impaired in this patient as a result of posterior parietal damage. By contrast the semantic representation for object identification would be intact.

Adult↗
PubMed1994

Impairments of movement execution in unilateral neglect: a kinematic analysis of directional bradykinesia.

A kinematic analysis was performed on goal-directed movements made by 14 patients with right hemisphere damage and left unilateral neglect (seven mild, seven severe), and 14 healthy controls. Leftward and rightward pen strokes of varying extents were made to targets of varying size on a centrally located digitising tablet. While mild unilateral neglect patients performed like controls, patients with severe unilateral neglect were slower to initiate leftward than rightward strokes and were slow and inefficient in movement execution. Leftward strokes made by severe unilateral neglect patients were characterised by prolonged movement time, lower peak velocity and departed from optimal bell-shaped velocity profiles. Their leftward strokes also showed prolonged accelerative phases, implying difficulties in force production, while the high proportion of their total movement time spent in decelerating with rightward strokes suggested an abnormal emphasis on terminal visual guidance. Leftward strokes made by these patients also contained more submovements than rightward strokes, suggesting poor force control. An impaired internal representation of the location of left-sided targets and desired movement trajectories in severe unilateral neglect causes breakdown in the temporal control of goal-directed movements.

Aged↗