Biomedical subjects

Paul R Davidson

Publications and source records attributed to Paul R Davidson.

10 recordsLinked to original sources

PubMed2006

Frequent lapses of responsiveness during an extended visuomotor tracking task in non-sleep-deprived subjects.

We investigated the occurrence of lapses of responsiveness (lapses) in 15 non-sleep-deprived subjects performing a 1D continuous tracking task during normal working hours. Tracking behaviour, facial video, and electroencephalogram (EEG) were recorded simultaneously during two 1-h sessions. Rate and duration were estimated for lapses identified by a tracking flat spot and/or video sleep. Fourteen of the 15 subjects had one or more lapses, with an overall rate of 39.3 +/- 12.9 lapses per hour (mean +/- SE) and a lapse duration of 3.4 +/- 0.5 s. We also found that subjects' performance improved towards the end of the 1-h long session, even though no external temporal cues were available. Spectral power was found to be higher during lapses in the delta, theta, and alpha bands, and lower in the beta, gamma, and higher bands, but correlations between changes in EEG power and lapses were low. In conclusion, lapses are a frequent phenomenon in normal subjects - even when not sleep-deprived - engaged in an extended monotonous continuous visuomotor task. This is of particular importance to the transport sector in which there is a need to maintain sustained attention for extended periods of time and in which lapses can lead to multiple-fatality accidents.

Adolescent↗

PubMed2006

Canadian psychiatry residency training programs: A glance at the management structure.

OBJECTIVES: To describe the administrative functioning of all current Canadian psychiatry residency training programs (RTPs) and to suggest available improvements to existing systems. METHOD: We obtained data about the 2004 RTPs by distributing 2 questionnaires to all Canadian psychiatry RTPs. RESULTS: Residency program committees (RPCs) are mainly consultative and carry only a small amount of the workload of managing a residency program. Program directors (PDs) manage more than 80% of the work and report that the time allowance to perform their duties is suboptimal. PDs remain in office for about 5 years, departing during or at the end of a predetermined second term. CONCLUSION: RPCs bear only a small amount of the workload generated by the RTP. We piloted administrative changes that led to more equitable work distribution.

Canada↗

PubMed2005

Widespread access to predictive models in the motor system: a short review.

Recent behavioural and computational studies suggest that access to internal predictive models of arm and object dynamics is widespread in the sensorimotor system. Several systems, including those responsible for oculomotor and skeletomotor control, perceptual processing, postural control and mental imagery, are able to access predictions of the motion of the arm. A capacity to make and use predictions of object dynamics is similarly widespread. Here, we review recent studies looking at the predictive capacity of the central nervous system which reveal pervasive access to forward models of the environment.

Brain↗

PubMed2005

Common encoding of novel dynamic loads applied to the hand and arm.

In manual action, the relationship between a given motor command and the ensuing movement depends on the dynamics of both the arm and hand-held objects. Skilled performance relies on the brain learning both these dynamics, and previous studies have examined how people adapt to novel loads applied to either the hand or the arm. In this study, we ask whether these different kinds of load are represented independently as a result of changes in cutaneous feedback and hand-arm coordination. We used a robotic apparatus that could either apply forces to an object held in the subject's hand or directly to the segments of the arm. We tested whether subjects could retain learning of a force field applied to the hand after subsequently experiencing the opposing field applied to the arm (or vice versa), or whether retrograde interference would be observed. In separate experiments, we used force fields and torque fields that were linearly related to either hand or joint velocities, respectively. Our finding of complete interference between opposing fields suggests that loads applied to the arm and hand are not represented independently by the sensorimotor system. This interference occurred despite markedly different cutaneous inputs that were directly related to the movement task. This result suggests that the brain represents dynamics independently of these sensory inputs. In addition, we found that the rate at which subjects adapted to a given force field, specified either in hand or joint coordinates, was independent of whether the forces were applied to the hand or arm segments.

Adult↗

PubMed2004

Scaling down motor memories: de-adaptation after motor learning.

Although adaptation to novel motor tasks is sometimes a very slow process, de-adaptation is usually extremely rapid. Such rapid de-adaptation is seen in dynamic learning in which subjects can take hundreds of movements to learn a novel force environment but only a few movements to de-adapt back to a normal or "null" force environment. We investigated whether this effect is unique to the null environment or reveals a more general rapid adaptation mechanism by studying how subjects behave when their dynamic environment changes. We observed that after learning a dynamic force field, subjects took longer to de-adapt when the forces were turned off than to adapt to a novel scaled-down version of the experienced field. This demonstrates that rapid adaptation is not unique to the "null" force environment. Moreover, we examined subjects' ability to adapt from a learned field to either a scaled down field or to a field in which the sign of the forces changed. Even though in both conditions the required change in force output was identical, subjects were significantly faster at adapting to the scaled down field. The result suggests that rapid de-adaptation reflects a capacity to scale down the relative contribution of existing control modules to the motor output.

Adaptation, Physiological↗

PubMed2004

Internal models underlying grasp can be additively combined.

Our ability to additively combine two learned internal models was investigated by studying the forces people generate when lifting objects with a precision grip. Subjects were required to alternately lift two objects of identical physical appearance but differing weight. Grip force scaling prior to lift-off was used to estimate the output of the internal model associated with each object. Appropriate internal models were formed when alternately lifting two objects of different weight. The objects were then combined by stacking them one upon the other, and the combined object was lifted. Results show that subjects can additively combine internal models of object dynamics but the sum is biased by a default estimate of the object's weight.

Adult↗

PubMed2003

Motor learning and prediction in a variable environment.

Traditional studies of motor learning and prediction have focused on how subjects perform a single task. Recent advances have been made in our understanding of motor learning and prediction by investigating the way we learn variable tasks, which change either predictably or unpredictably over time. Similarly, studies have examined how variability in our own movements affects motor learning.

Biomechanical Phenomena↗

PubMed2003

Delirium in hospital: an underreported event at discharge.

OBJECTIVE: Delirium, an important event in hospital, is associated with significant mortality and morbidity. Most patients with delirium recover fully; however, when left untreated, delirium may progress to stupor, coma, or death. Delirium is less likely to resolve completely in elderly patients in whom persistent cognitive deficits commonly occur. The extent to which this information is available to family doctors after discharge was investigated. METHOD: A total of 31 patients with delirium who were referred to consultation-liaison psychiatry were assessed using standardized measures. Medical services completed discharge summaries on these patients; a chart review captured the extent to which the diagnosis of delirium and the involvement of psychiatry was recorded in the discharge summaries. RESULTS: In structured discharge summaries, a reference to delirium occurrence was found in 55% of cases. In unstructured discharge summaries, the reporting was much lower (16% of cases). Delirium was more likely to be reported in women than in men, when it was more severe, or when it was the principal reason for admission, rather than when it occurred during an admission for some other reason. CONCLUSIONS: Delirium episodes that occur during a period of hospitalization for treatment of any medical disorder are underreported, even when specifically diagnosed. Structured discharge summaries tend to increase the rate of reporting.

Aged↗

PubMed2002

Simulating closed- and open-loop voluntary movement: a nonlinear control-systems approach.

In many recent human motor control models, including feedback-error learning and adaptive model theory (AMT), feedback control is used to correct errors while an inverse model is simultaneously tuned to provide accurate feedforward control. This popular and appealing hypothesis, based on a combination of psychophysical observations and engineering considerations, predicts that once the tuning of the inverse model is complete the role of feedback control is limited to the correction of disturbances. This hypothesis was tested by looking at the open-loop behavior of the human motor system during adaptation. An experiment was carried out involving 20 normal adult subjects who learned a novel visuomotor relationship on a pursuit tracking task with a steering wheel for input. During learning, the response cursor was periodically blanked, removing all feedback about the external system (i.e., about the relationship between hand motion and response cursor motion). Open-loop behavior was not consistent with a progressive transfer from closed- to open-loop control. Our recently developed computational model of the brain--a novel nonlinear implementation of AMT--was able to reproduce the observed closed- and open-loop results. In contrast, other control-systems models exhibited only minimal feedback control following adaptation, leading to incorrect open-loop behavior. This is because our model continues to use feedback to control slow movements after adaptation is complete. This behavior enhances the internal stability of the inverse model. In summary, our computational model is currently the only motor control model able to accurately simulate the closed- and open-loop characteristics of the experimental response trajectories.

Adaptation, Biological↗

PubMedDate not supplied

Administrative restructuring of a residency training program for improved efficiency and output.

OBJECTIVES: Canadian residency training programs (RTP) have a program director (PD) and a residency program committee (RPC) overseeing program administration. Limited guidance is available about the ideal administrative structure of an RTP. This article describes administrative load in Canadian RTPs, presents a novel approach to delegating core administrative tasks within the RTP, and provides initial impressions of positive outcomes following implementation of this new system. METHOD: All PDs of Canadian psychiatry RTPs were surveyed with respect to their program administrative structure, involvement of their training committees, and the percentage of work done by the PD compared to the rest of the RPC. At Queen's University, program domains were created representing well-defined areas within the RTP, each being assigned a program domain manager. RESULTS: RPCs were mainly consultative, averaging 14 members. The average PD: RPC workload ratio was 80:20. Three programs allowed for 50% of the program director's time to be dedicated to serving that position, with an average time dedication of 37%. CONCLUSION: The position of PD in psychiatry requires an average of 37% of the program director's time, while carrying an estimated 82% of the administrative workload. The program domain manager administration system implemented at Queen's University enabled the PD to be simultaneously up to date with all major areas of the program while experiencing a substantial decrease in the administrative workload, achieved through increased work contribution of the RPC. This system encourages closer involvement of RPC members in decision making and development of their program domains, allowing the PD more time for developing, implementing and overseeing innovations across the RTP spectrum. Furthermore, it has led to a PD: RPC workload shift from a ratio of 90:10 to one of about 60:40. Essentially, this resulted in a more efficient and adaptable RPC and RTP.

Canada↗