Douglas L. Weeks

Temporal constraints in the control of prehensile movement.

Three experiments were conducted to investigate the control of the manipulation (i.e., finger-thumb aperture) and transportation (i.e., wrist velocity) components in prehensile movement (Jeannerod, 1981, 1984). In all experiments, subjects were seated and instructed to grasp a dowel mounted on a joystick following a discrete movement over a set distance. Thus, the amount of dowel movement following the grasp could be determined. In Experiment 1, the tolerance (i.e., the amount of allowable dowel movement) was manipulated using a computer-generated boundary around the dowel. The results indicated that the transportation component changed dependent on the tolerance condition, and there were trends that maximum aperture was also affected. Experiment 2 manipulated both tolerance and dowel size (i.e., diameter) factorially in a within-subject design. Dowel size affected only the manipulation component, supporting Jeannerods (1981) earlier work, but tolerance clearly influenced both components. Experiment 3 investigated Wing, Turton, and Frasers (1986) proposition that speed of movement influences aperture size. Distance and movement time were combined factorially to produce conditions with different average velocities. Maximum aperture was dependent on the movement time rather than the speed of movement. The relation between the control of the components was examined by using a new method of calculating within-trial correlations between aperture size and wrist velocity in Experiments 2 and 3. The correlations were related to the temporal aspects of the movement with higher correlations in the rapid movement time conditions. Also, the temporal occurrence of maximum aperture remained invariant across the different movement conditions. In general, the results suggest a strong functional linkage between the two components, which may be dependent on the temporal characteristics of the movement.

Tests for normality and measures of skewness and kurtosis: their place in research reporting

Even though research interest is typically greatest for questions pertaining to central tendency and, to a lesser degree, variability, knowledge about the nature of a measure or variable is impoverished when information about the shape of the frequency distribution is ignored. This paper makes the point that descriptive and inferential measures of non-normality should be a routine part of research reporting, along with graphic displays of the frequency distribution of important variables. This point is especially true for research involving measures with non-arbitrary metrics where the shape of the distribution is not affected by measurement artifacts.

Toward Automating Clinical Assessments: A Survey of the Timed Up and Go

Older adults often suffer from functional impairments that affect their ability to perform everyday tasks. To detect the onset and changes in abilities, healthcare professionals administer standardized assessments. Recently, technology has been utilized to complement these clinical assessments to gain a more objective and detailed view of functionality. In the clinic and at home, technology is able to provide more information about patient performance and reduce subjectivity in outcome measures. The timed up and go (TUG) test is one such assessment recently instrumented with technology in several studies, yielding promising results toward the future of automating clinical assessments. Potential benefits of technological TUG implementations include additional performance parameters, generated reports, and the ability to be self-administered in the home. In this paper, we provide an overview of the TUG test and technologies utilized for TUG instrumentation. We then critically review the technological advancements and follow up with an evaluation of the benefits and limitations of each approach. Finally, we analyze the gaps in the implementations and discuss challenges for future research toward automated self-administered assessment in the home.

A Comparison of Knowledge of Results Scheduling Methods for Promoting Motor Skill Acquisition and Retention

Providing knowledge of results (KR) to a learner about each trial in a series of trials only after the series is completed is termed summary KR. A variation of summary KR is average KR, in which KR is presented as an average value about the series of trials. This study compared groups receiving either average KR, summary KR, or KR following every attempt in acquisition of a force production task. Following acquisition, groups performed no-KR immediate and long-term retention tests. Analysis of variable error revealed group main effects and group by block interactions in acquisition and long-term retention. Post hoc tests indicated that differences were due primarily to inconsistent performance of the group receiving KR following each acquisition attempt. Post hoc tests did not, however, indicate differences between the average KR and summary KR groups in acquisition or retention. It was concluded that average and summary KR promote consistency in performance in acquisition, with this stability in responding carried over to retention performance.

Predicting potential postdischarge adverse drug events and 30-day unplanned hospital readmissions from medication regimen complexity.

Objectives To determine whether medication regimen complexity (MRC) could predict likelihood for occurrence of potential adverse drug events (ADEs), unplanned 30-day hospital readmission, or 30-day emergency department use in patients transitioning from hospital to home care. Methods Hospital discharge medication lists and medication lists constructed during visits to patients’ homes were analyzed for 213 participants. MRC was quantified with the Medication Regimen Complexity Index (MRCI). The potential for ADEs was based on medication discrepancies detected between the discharge and patient reported home medication lists. Unplanned acute care utilization in the 30 days after index hospitalization was tracked. Logistic regression analyses were used to approximate the odds for an ADE and postdischarge acute care utilization from MRCI scores. Results Home medication lists were less complex than hospital discharge medication lists. High home medication list MRCI scores increased the odds more than 4-fold for a potential ADE (P < 0.001). High discharge medication list MRCI scores increased the odds more than 5-fold for an unplanned 30-day hospital readmission (P = 0.026). High regimen complexity did not significantly elevate odds for emergency department use. Conclusions MRC was predictive of patients’ potential for ADEs and unplanned hospital readmission. MRC may be useful in identifying patients that would benefit from additional transitional care interventions. Results indicate that simplifying medication regimens may favorably impact postdischarge outcomes.

The perceptual guidance of grasping a moving object

Abstract The purpose of this experiment was to examine the type of strategy subjects used in catching an object approaching on a non-intersection trajectory at different, but predictable, constant velocities. A small treadmill mounted on a table top supported a target dowel to be ‘caught’ by the subjects hand, which rested at the end of the treadmill. The treadmill produced six constant velocity approaches administered in blocks of trials in ascending order. The object and the subjects finger movements were kinematically examined using a three-dimensional motion analysis system. The results indicated that a type of perceptual-motor coupling between the value of the optical variable tau (τ) at initiation of the catching movement and the duration of the catching movement was being used, rather than a consistent τ strategy. In addition, a relatively constant ratio of the value of τ at initiation and τ at the start of the catching movement was observed across the six object velocities. These results show limitations in the use of a critical τ strategy, at least in this type of task. A functional relationship between the information in τ and how a movement is performed may allow for greater flexibility in the coordination of interceptive acts.

The Role of Variability in Practice Structure when Learning to Use an Upper-Extremity Prosthesis

&NA; This study contrasted two different practice schedules for learning to use a prosthetic simulator that mimicked an upper‐extremity prosthesis with a voluntary‐close terminal device. The purpose was to determine an efficient practice schedule for learning to perform prehension skills that could be employed by people learning to use an actual prosthesis after amputation. Forty‐eight participants were randomly distributed into two groups for skill acquisition training: those who practiced three different prehension tasks with the simulator in a random practice order or those who practiced the three tasks with the simulator under a blocked practice order. During acquisition, the groups practiced the three tasks on two consecutive days. On the third day, two different tests of learning were administered: a retention test on the tasks practiced in acquisition and an intertask transfer test on three tasks similar to those practiced in acquisition. Both the random and blocked groups showed significant improvements in initiation time and movement time to perform each task across the 2 days of acquisition. Thus, structured practice, regardless of degree of “randomness” inherent in the schedule, promoted functional use of the prosthesis. Both practice schedules were equally effective for promoting skill retention; however, in intertask transfer, the random acquisition group demonstrated significantly greater proficiency in performing the new tasks than the blocked acquisition group. Persons learning to use an upper‐extremity prosthesis may be better able to transfer skill to new prehension tasks by practicing under random practice conditions.

Pilot Randomized Trial Comparing Intersession Scheduling of Biofeedback Results to Individuals with Chronic Pain: Influence on Psychologic Function and Pain Intensity.

ObjectiveThe objective of this study was to compare the effectiveness of two biofeedback schedules on long-term improvement in physical and psychologic reactivity to chronic nonmalignant pain. DesignThis study is a prospective, randomized pilot trial. MethodsTwenty adults with chronic pain engaged in heart rate variability (HRV) biofeedback training for nine sessions with HRV presented visually. Two groups, formed by random assignment, were compared: The faded feedback group received concurrent visual HRV biofeedback in session 1, with the amount of biofeedback systematically reduced for ensuing sessions so that, by session 9, the participants were controlling HRV without external feedback. The full feedback group received visual HRV biofeedback continuously across all sessions. Outcome measures assessed at baseline, immediately after the program, and 3 mos after the program included pain intensity, fear-avoidance beliefs, and self-report physical functioning. Use of biofeedback skills was also assessed 3 mos after the program. Nominal variables were analyzed with &khgr;2. Continuous measures were analyzed with repeated-measures analyses of variance. ResultsThe faded feedback schedule resulted in greater use of biofeedback skills at 3 mos and improved pain intensity and fear-avoidance beliefs after the program and at 3 mos. Physical functioning did not differ between groups. ConclusionsSystematically reducing the frequency of external visual feedback during HRV biofeedback training was associated with reduced reactivity to chronic pain. Results of this pilot study should be confirmed with a larger randomized study.

Weight Discrimination Using an Upper-Extremity Prosthesis

A person with an upper-extremity amputation who uses prosthesis often engages in prehension activities that require the grasping and manipulation of objects. As a result of the amputation, such prehension activities are clearly performed with a significant loss of proprioceptive information. It has been shown in the psychophysical literature that losses in proprioceptive information impair both perceptual judgments (such as weight discrimination) and motor function in nonamputee participants. It is not known whether similar impairments occur with users of upper-extremity prosthetic devices, therefore two experiments were performed to investigate the ability of individuals using an upper-extremity prosthesis to discriminate weight of hand-held objects. In the first experiment, we compared weight discrimination of nonamputees using either their anatomical limb or a simulated upper-extremity prosthesis. In addition, we included a person with a congenital limb deficiency who was an experienced prosthetic user. The results revealed that weight discrimination was poorer with the simulated prosthesis than with the anatomical hand. Surprisingly, there were no significant differences between the anatomical hand condition of this group of participants and the person with a congenital limb deficiency. In the second experiment, we found that withdrawing visual information from the same person with a congenital limb deficiency did not degrade the ability to discriminate weight. These results suggest that experience using a prosthesis may overcome the initial difficulties in discriminating weight. Discrimination may improve because the experienced prosthetic user learns to rely on other sources of proprioceptive information in making perceptual judgments and/or because the user develops greater control over the prosthesis.

Premovement posture and focal movement velocity affects on postural responses accompanying rapid arm movement

Abstract Coordination of intentional upper limb movement concurrent with supporting postural activity was investigated in adult males under varying task conditions. Seven subjects performed a 60 deg rapid elbow flexion (focal movement) to a target in movement times of 170, 195, or 220 ms while standing. Measurement of center of pressure via a force platform revealed that subjects adopted individual premovement postural preferences such that locus of center of pressure resided in one predominant quadrant of the foot. Each premovement postural preference was accompanied by one most common postural muscle onset sequence as indicated by bilateral EMG analysis of rectus femoris and biceps femoris. In addition, onset times for postural muscles exhibiting anticipatory postural activity occurred earlier relative to biceps branchii as focal movement velocity increased. The finding that each premovement postural condition was accompanied by one particular postural muscle onset sequence suggested that postural synergies were flexibly organized with respect to onset sequence.