Unexpected inertial loading in rapid reversal movements: Violations of equifinality

Emotional Labor in Health Care: The Moderating Roles of Personality and the Mediating Role of Sleep on Job Performance and Satisfaction

The objective of this study is to investigate the effects of emotional labor on job performance and satisfaction, as well as to examine the mediating effect of sleep problems and the moderating effects of personality traits. A time-lagged study was conducted on 864 health professionals. Scales for emotional labor, sleep, personality traits, and job satisfaction were used and job performance data was obtained from records maintained by human resources. Structural equation modeling was performed to investigate the relations. Sleep problems only partially mediated the relationship between surface acting and job satisfaction but completely mediated the relationship between surface acting and job performance. Several personality traits were shown to moderate the relationship between surface acting and sleep problems. The effects were stronger for people with low agreeableness and high neuroticism. The relationship between high levels of deep acting and low levels of sleep problems was more pronounced in individuals with low extraversion. Supervisors should be conscious of emotional labor in the work context and provide necessary deep acting training to facilitate emotional regulation.

Optimizing rapid aiming behaviour: movement kinematics depend on the cost of corrective modifications

Recent studies have shown that the initial impulse associated with goal-directed aiming movements typically brings the limb to a position short of the target. This is because target overshooting is associated with greater temporal and energy costs than target undershooting. Presumably these costs can be expected to vary not only with the muscular forces required to move the limb, but also the gravitational forces inherent in the aiming task. In this study we examined the degree to which primary movement endpoint distributions depend on the direction of the movement with respect to gravity. We hypothesized that the magnitude of an undershoot bias would be greatest for downward movements because target overshooting necessitates a time and energy consuming movement reversal against gravity. Participants completed rapid aiming movements toward targets located above and below, as well as proximal and distal to a central home position. Movements were made both with and without additional mass attached to the limb. Although movement time did not vary with experimental condition, primary movement endpoint distributions were consistent with our predictions. Specifically, both greater undershooting and greater endpoint variability was associated with downward aiming movements. As well, a greater proportion of the overall movement time was spent in the corrective phase of the movement. These results are consistent with models of energy minimization that posit an inherent efficiency of control and hold that movements are organized to minimize movement time and energy expenditure and maximize mechanical advantages.

The influence of movement cues on intermanual interactions

In two experiments, we studied intermanual interactions in bimanual reversal movements and bimanual aiming movements. Targets were presented on a monitor or directly on the table on which the movements were produced. Amplitudes for each hand were cued symbolically or spatially either in advance of an imperative signal or simultaneous with it. In contrast to findings of Diedrichsen et al. (Psychological Science, 12, 493-498, 2001), reaction times for different-amplitude movements were longer than for same-amplitude movements both for symbolic and spatial cues presented on the monitor and directly on the table. However, with symbolic cues the effect of the relation between target amplitudes was considerably stronger than with spatial cues, no matter where the cues were presented. Intermanual correlations of amplitudes, movement times, and reaction times were smaller with different than with same target amplitudes, and this modulation was more pronounced when targets and cues were presented on the monitor than when they were presented on the table. The findings are taken to suggest that the basic reaction-time disadvantage of different-amplitude movements results from interference between concurrent processes of amplitude specification. Additional factors like interference between concurrent processes of mapping cues on movement characteristics may add strongly to it.

The effects of weak perturbations on rapid finger oscillations

Movement control can be position based or amplitude based; in the first case the frame of reference is fixed, while in the second case the origin is at the start of each movement so that in series of movements errors are propagated. In movements aimed at a target the kind of control is task dependent, though the majority of findings suggest a stronger weight of amplitude-based control. In rapid finger oscillations which do not require visuo-motor transformations, control turned out to be position based as revealed by a lack of propagation of small shifts of angular position induced by brief mechanical perturbations; the only effect of the perturbations in addition to the immediate mechanical effect on movement amplitude was enhanced myoelectric activity in both agonists and antagonists which showed up with some delay. The finding of position-based control points to the functional importance of the mechanical characteristics of peripheral musculo-skeletal systems in rapid limb oscillations.

Intentional Compensation for Selective Loading Affecting Human Gait Phases

The locomotor strategies used by 12 subjects, instructed to hold their walking speed constant, were examined under various dynamic conditions in order to determine the means by which subjects can act upon their basic locomotor synergy. The dynamic conditions were modified either by adding a load or applying an impeding force. These modifications were designed to selectively affect either the stance phase or the swing phase. The results show that (a) subjects were able to rapidly calibrate their efforts to hold their walking speed constant, (b) in all conditions, the same walking speed was achieved with the same stride lengths and durations, and (c) at the within-cycle level, a change in duration synergically affected both phases and not just the perturbed one. The above results are discussed in terms of intentionally controlled parameters. Because cadence is closely linked to walking speed, it can be used as feedback; the control of walking speed in our experiments may thus be achieved simply by increasing the exerted force until the same cadence is produced.