Biomedical subjects

P Haggard

Publications and source records attributed to P Haggard.

11 recordsLinked to original sources

PubMed1999

On the relation between brain potentials and the awareness of voluntary movements.

We investigated the relation between neural events and the perceived time of voluntary actions or the perceived time of initiating those actions using the method of Libet. No differences were found in either movement-related potentials or perceived time of motor events between a fixed movement condition, where subjects made voluntary movements of a single finger in each block, and a free movement condition, in which subjects chose whether to respond with the left or the right index finger on each trial. We next calculated both the readiness potential (RP) and lateralised readiness potential (LRP) for trials with early and late times of awareness. The RP tended to occur later on trials with early awareness of movement initiation than on trials with late awareness, ruling out the RP as a cause of our awareness of movement initiation. However, the LRP occurred significantly earlier on trials with early awareness than on trials with late awareness, suggesting that the processes underlying the LRP may cause our awareness of movement initiation.

Adult↗

PubMed1998

Coordination of hand aperture with the spatial path of hand transport.

We have investigated the coordination of hand aperture with the spatial path of hand transport in prehensile movement by comparing straight prehensile movements with curved movements, in which subjects had to pass over a "via point" marked on the work surface before picking up an object in the target location. Spatial plots of hand aperture against hand transport showed that the preshaping of the hand to prepare an appropriate grasp was delayed in the curved movements relative to the straight movements, with most of the preshaping of the hand occurring after passing the via point, even when the via point occurred late in the course of the movement. The postponement of hand preshaping was apparently not due to subjects' segmenting the movement into two completely separate portions preceding and following the via point, since some degree of hand opening often occurred before the via point. We suggest that the delay in hand opening in curved movements involves a scheduling process, which uses information about hand transport to set an appropriate hand aperture.

Adult↗

PubMed1998

12-month outcome of patients with bipolar disorder following hospitalization for a manic or mixed episode.

OBJECTIVE: The authors studied the 12-month course of illness following hospitalization for a manic or mixed episode of bipolar disorder to identify potential outcome predictors. METHOD: They recruited 134 patients with DSM-III-R bipolar disorder who were consecutively admitted for the treatment of a manic or mixed episode. Diagnostic, symptomatic, and functional evaluations were obtained at the index hospitalization. Patients were reevaluated at 2, 6, and 12 months after discharge to assess syndromic, symptomatic, and functional outcome. Factors associated with outcome were identified by using multivariate analyses. RESULTS: During the 12-month follow-up period, there were no significant differences in outcome between patients with manic compared with mixed bipolar disorder. Although syndromic recovery occurred in 48% of the overall group, symptomatic recovery occurred in only 26% and functional recovery in only 24%. Predictors of syndromic recovery included shorter duration of illness and full treatment compliance. Medication treatment compliance was inversely associated with the presence of comorbid substance use disorders. Symptomatic and functional recovery occurred more rapidly and in a greater percentage of patients from higher social classes. CONCLUSIONS: A minority of patients with bipolar disorder achieved a favorable outcome in the year following hospitalization for a manic or mixed episode. Shorter duration of illness, higher social class, and treatment compliance were associated with higher rates of recovery and more rapid recovery.

Adolescent↗

PubMed1997

Coordinating actions.

The motor system composes complex actions by combining simpler submovements. This presumably involves sharing information about the progress of one submovement with the centres controlling another submovement, to ensure that the second happens in an appropriate relation to the first. This process is called coordination. In this paper I discuss evidence that coordinating actions indeed involves an active process of sharing information about the current state of movements. Coordination appears to be qualitatively different from the process of reacting to external stimuli. This may reflect the importance of predictive representations in coordination. Finally, the processes underlying coordination appear to be organized in a response-specific fashion, as a number of relatively independent circuits. The development and tuning of these circuits may, in part, be what makes an action "skilled".

Analysis of Variance↗

PubMed1996

Spatial patterns in the control of human arm movement.

Generalized Procrustes analysis was used to investigate the spatial paths of pointing movements. In Experiment 1, 3 participants produced similar spatial paths of the hand when repeating a pointing movement many times, despite variability in the position and orientation of the movements. The average spatial path indicates a fundamental spatial pattern of the motor system, or motor primitive. This pattern varied across the workspace. Anterioposterior movements were straight, but repeated movements had variable spatial patterns. Lateral movements were curved away from the body but had regular spatial patterns. Experiment 2 extended these results to movements of different amplitudes in 7 participants. The motor primitive seems to be abandoned at the end of the movement in favor of final adjustments to bring the hand to the target position. In Experiment 3, the same participants produced similar motor primitives both with and without vision.

Arm↗

PubMed1995

Patterns of coordinated multi-joint movement.

In multi-joint reaching movements, the motor system may choose any one of an infinite set of possible joint rotations to move the hand between given start and target positions. In order to find out whether reaching movements are represented in Cartesian hand coordinates or in joint coordinates, it is necessary to measure whether hand paths or joint paths have lower variability. We have measured hand paths and rotations of shoulder, elbow and wrist joints simultaneously in five subjects reaching in four orientations in the horizontal plane. As in earlier studies, we found a preference for nearly straight hand paths, despite different patterns of joint rotation for different orientations of movement. However, movements in three of four orientations showed a single principal joint, which rotated essentially without reversals. This may reflect optimisation in the motor system, preferring the simplest pattern of joint control for a desired hand path. We used generalised Procrustes analysis to quantify the variability in shape of repeated paths in hand space and joint space. Results showed that hand paths were less variable than the joint angles used to realise them, due to the kinematic redundancy of the limb, suggesting that hand paths, rather than joint angles, are directly represented by the motor system. Nevertheless, movements with straighter hand paths, on average, and those requiring coordinated activity at both shoulder and elbow joints also showed more variability in the shape of the hand path. Other orientations such as movement across the body use primarily a single joint and are less variable at the cost of a slightly curved path. These results suggest that coordinating multiple joints to produce a straight hand path has a definite computational cost. The motor system may perform a trade-off between the benefits of planning reaching movements as straight hand paths and the computational simplicity of executing them using patterns of joint rotation which simplify multi-joint coordination.

Adult↗

PubMed1995

Coordinated responses following mechanical perturbation of the arm during prehension.

We have investigated how the control of hand transport and of hand aperture are coordinated in prehensile movements by delivering mechanical perturbations to the hand transport component and looking for coordinated adjustments in hand aperture. An electric actuator attached to the subject's right arm randomly pulled the subject backwards, away from the target, or pushed them towards it, during a quarter of the experimental trials. A compensatory adjustment of hand aperture followed the immediate, mechanical effects of the perturbation of hand transport. The adjustment appeared to return the subject towards a stereotyped spatial relation between hand aperture and hand transport. These spatial patterns suggest how the two components may be coordinated during prehension. A simple model of this coordination, based on coupled position feedback systems, is presented.

Adult↗

PubMed1995

Damage to cerebellocortical pathways after closed head injury: a behavioural and magnetic resonance imaging study.

The objective was to investigate the anatomical substrate of ataxia seen after severe head injury. Five patients were recruited from present and former inpatients at Rivermead Rehabilitation Centre. All patients had had a closed head injury and all had cerebellar type ataxia. Four normal controls were also studied. Brain MRI, clinical examination, computer based recording, and analysis of visuomotor tracking were carried out. Focal damage was found in the superior cerebellar peduncle in all five ataxic patients. The patients' tracking movements showed profound tremor, and unusual reliance on visual feedback. Ataxia seen after severe head injury can arise from damage to the superior cerebellar peduncle, which may interfere with the cerebellocortical circuits involved in coordinated movement.

Adult↗

PubMed1994

Coordination of aimed movements in a case of unilateral cerebellar damage.

We have studied multi-joint arm movements in a patient with right cerebellar damage. Our patient's kinetic tremor was reduced in the absence of visual feedback, but increased when performing a concurrent cognitive task. We suggest that her kinetic tremor reflects use of a slow cortical feedback circuit for error-corrections during movement. Analysing the spatial relation between hand aperture and hand transport in prehensile movements, we found preserved strategic, trial-to-trial coordination, but impaired reactive, within-trial coordination. We conclude that the proprioceptive representations provided by the normal cerebellum play an important role in coordinating multi-joint movement.

Adult↗

PubMed1993

I think, therefore I manage.

Thirty healthcare managers were asked about the moral assumptions underlying their attitudes to the job. Pat Haggard reports her findings.

Administrative Personnel↗

PubMed1991

Remote responses to perturbation in human prehension.

This experiment investigated how the control of hand transport and of hand aperture are coordinated in reaching and grasping movements. An electric actuator attached to the subject's right arm delivered mechanical perturbations randomly during a quarter of the experimental trials. A remote, compensatory adjustment of hand aperture followed the immediate, mechanical affects of the perturbation of hand transport. The invariant spatial and temporal characteristics of the response suggest how the two systems may be coordinated during prehension.

Adult↗