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C J Worringham

Publications and source records attributed to C J Worringham.

14 recordsLinked to original sources
PubMed1990

Practice effects on the preprogramming of discrete movements in Parkinson's disease.

The effects of practice on the simple and choice reaction times (RTs) of Parkinson's disease (PD) and control subjects in a discrete aiming task were analysed. For controls, practice led to a selective decrease in choice RTs, as has been reported previously. An opposite effect was seen in the PD group, with little change in choice RTs and substantial reduction in simple RTs. The results suggest that PD subjects can use advance information to initiate discrete movements more rapidly, but that this ability to "preprogramme" movements requires practice. Reconciliation of these results with studies reporting an inability to preprogramme in PD are made in a discussion of task characteristics which may allow or preclude preprogramming.

Attention↗
PubMed1989

Force production characteristics in Parkinson's disease.

This experiment examined the preparation and the production of isometric force in Parkinson's disease (PD). PD patients, elderly, and young subjects generated force levels that were a percentage of their maximum (15, 30, 45, and 60%). Subjects were cued on the upcoming target force level and they were asked to produce the required response as fast as possible. PD patients showed a similar progression of force variability and dispersion of peak forces to that of control subjects, implying they have an accurate "internal model" of the required forces. Force production impairments were seen, however, at the within-trial level. PD patients had more irregular force-time curves that were characterized by changes in the rate of force production. The results suggest a more "noisy" output from the motor system and an inability to produce smooth forces. PD patients were also substantially slower in initiating a force production and the delay was localized in the pre-motor reaction time.

Adolescent↗
PubMed1989

Preparatory processes in a case of hemi-parkinsonism.

Reaction times and movement times were recorded in a subject with parkinsonian symptoms confined largely to the left side of the body. Advance information concerning the movement was varied, being with complete, partial or no preparation. The results suggest that processing of preparation for the movement is not qualitatively different for the more affected side, but is substantially slowed.

Female↗
PubMed1989

Operator orientation and compatibility in visual-motor task performance.

This experiment assessed three alternative forms of directional compatibility between control and display movement, to examine their degree of dependence on the orientation of the operator. Subjects performed a target acquisition task in each of 11 conditions which embodied the three compatibility types alone or in combination. Visual-motor (VM) compatibility was defined as display movement in a given direction in the subject's visual field produced by control movement in the same direction in the subject's 'virtual' visual field (i.e., were he or she looking at the control rather than the display). Control-display (CD) compatibility referred to congruence between control and display movements. Visual-trunk (VT) compatibility was present if a control movement was in the same direction relative to the operator's trunk as the movement of the display in the visual field. VM compatibility produced performance superior to that under CD or VT compatible conditions in all phases of the task, and was independent of the subject's physical orientation and of the target direction. Visual-motor compatibility appears to reflect a basic and general relationship between visual and motor codes in the central nervous system, and may prove a useful basis for reducing errors and enhancing performance in certain human-machine systems.

Adult↗
PubMed1988

The preparation and production of isometric force in Parkinson's disease.

Subjects with Parkinson's disease (PD) and age-matched controls performed an isometric force production task, aiming at different target force levels without concurrent force feedback. Overall, PD subjects were as accurate as controls in attaining the target force levels, but executed the task differently. They had longer times to peak force and contraction durations, larger impulses and lower rates of force development, and force-time profiles with many more irregularities. They also initiated lower force contractions with longer latencies, unlike controls. The data suggest that PD subjects are deficient in the regulation of force and time parameters, rather than simply in force production. The ability to produce peak forces accurately limits the generality of previous assertions that PD subjects are heavily dependent on concurrent visual feedback.

Aged↗
PubMed1988

The control of bimanual aiming movements in Parkinson's disease.

The control of unimanual and bimanual aiming movements by Parkinson's disease and control subjects was examined. Despite greater bimanual movement initiation asynchrony and overall bradykinesia, the Parkinson's disease subjects were affected by the experimental manipulations in the same way as controls. Symmetrical and, more especially, asymmetrical bimanual movements required more preparation time and were executed more slowly by both groups than were unimanual movements. Both groups also showed temporal linkage of movements to targets of different extents--movements which have different movement times when performed unimanually, as well as of the faster and slower limbs. A majority in both groups over-compensated for asynchrony in bimanual movement initiation by modulation of movement times, but there was no group difference in this tendency. The results are discussed in terms of underlying motor control processes and with regard to previous evidence for impaired control of simultaneous movements in Parkinson's disease.

Aged↗
PubMed1987

Limb segment inclination sense in proprioception.

Two experiments were performed to determine if proprioceptive signals are perceived more readily in terms of limb segment inclinations to the vertical than as joint angles. Subjects attempted to match arm positions with the upper arms supported at different inclinations. Constant error data showed that, when instructed to match forearm inclinations to the vertical, subjects were very accurate. When required to match elbow joint angles, however, errors were strongly biased in the direction of matching forearm inclinations. The results support a view of proprioception as a system in which afferent signals related to the gravitational torques acting at joints lead to the perception of limb orientation rather than joint angles. Such a system would allow more efficient determination of the relationship of limb segments to external objects than would one based purely on joint angles.

Adult↗
PubMed1987

The programming and execution of movement sequences in Parkinson's disease.

Parkinsonian and neurologically normal subjects performed a finger-tapping task in which different sequence lengths had to be executed as rapidly as possible. For each response sequence, reaction time (RT), inter-tap-intervals (ITIs) and error patterns were recorded. It was found that the RT-sequence length relationship as well as the group ITI data were different for the two groups, indicative of impaired programming in the Parkinsonian subjects. This conclusion was supported by a relative dissociation of the first and subsequent taps and by a pattern of progressively increasing errors with longer tap sequences in the Parkinsonians.

Aged↗
PubMed1986

Movement preparation in Parkinson's disease. The use of advance information.

The effects of advance information on movement planning in parkinsonism were assessed by means of movement precuing. Using this technique, the response latencies of identical sets of movements were compared across conditions in which the degree and type of advance movement information were manipulated. Specifically, prior information concerning three movement dimensions (the direction and extent of forthcoming movements, as well as the limb to be used) was or was not provided. Eight patients with Parkinson's disease and 8 neurologically normal age-matched controls served as subjects. The experiment showed that the elevated reaction times of the Parkinsonian subjects are not primarily caused by delays in response selection. Estimates of specification times for each of the three dimensions showed only a modest slowing in parkinsonians. The specification of those movement dimensions unknown before the response signal appears to occur serially, and can occur in a variable order as in normals. Since parkinsonians can initiate movements with shorter latencies when partial or complete information is available, albeit more slowly than normals, we conclude that response selection and specification processes preceding rapid discrete movements are relatively unaffected by the disease. The overall slowness in movement initiation in parkinsonians as compared with normals may in part be caused by excessive delays in motor time and, in general, to those 'input' and/or 'output' processes which are unaffected by advance information.

Aged↗
PubMed1985

The contribution of gravitational torques to limb position sense.

An experiment is reported which examined whether gravitational torque acting about a joint is used by the CNS in elbow joint angle matching. Subjects were required to match the joint angles of their two limbs while the external torques acting about each elbow were systematically varied. It was found that when the matching limb was differentially loaded, the error in the produced reference angle corresponded to the directional prediction of a proposed gravitational torque hypothesis. The data suggest that torque sensation is an accessory source of information in limb positioning.

Adult↗
PubMed1985

Sensorimotor deficits related to postural stability. Implications for falling in the elderly.

The effects of age-related sensorimotor and central processing deficits on postural control are reviewed, and the paucity of knowledge about proprioceptive changes with age is noted. A model of processing stages in the production of responses to postural instability is outlined. Even slight response slowing produces disproportionate increases in clinically slow responses. Many aspects of postural responses are "cognitively penetrable". Research on falls should examine learned as well as automated behaviors.

Accidents↗