Measurements serve a purpose: a note on a possible use of natural measurements.
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Communication↗
Biomedical subjects
Herbert Heuer
Publications and source records attributed to Herbert Heuer.
The effects of muscle fatigue on rapid finger oscillations.
Two types of model for the control of rapid finger oscillations can be contrasted. According to the first type, any change of muscle characteristics induced by sustained isometric contractions should result in kinematic changes. According to the second type, kinematic characteristics should remain invariant while the timing of bursts of muscle activity exhibits compensatory adjustments. Following sustained isometric contractions of finger flexors and extensors, we observed essentially unchanged durations of the flexion and extension components of rapid finger oscillations, while the pattern of inter-burst intervals was modified so as to compensate the changed phasing of electromyographic bursts. These findings strongly suggest that even in extremely simple rapid finger oscillations motor control is configured to result in invariant kinematics.
Adolescent↗
Processes of task-set reconfiguration: switching operations and implementation operations.
When participants are asked to shift between four dimensionally organized tasks which differ in the type of judgment (numerical vs. spatial) and/or the judgment-to-response mapping (compatible vs. incompatible), a characteristic profile of shift costs can be observed. It can be accounted for in terms of two different types of operations: generalizing switching operations on a dimensionally organized set of task representations and implementation operations [T. Kleinsorge, H. Heuer, Psycholog. Res. 62 (1999) 300]. In a first experiment we corroborated our previous findings by way of a new procedure that makes it possible to estimate shift costs unconfounded by a number of factors that are likely to affect estimates of shift costs based on more conventional procedures. In a second experiment we investigated the endogenous and exogenous nature of the postulated types of operations. The characteristic profile of shift costs disappeared when long precue intervals (PCIs) were used. Augmented by a formal analysis, this finding suggests that both switching and implementation operations are endogenously controlled. In addition, there remained some residual shift costs which were essentially insensitive to the nature of the task shift but depended on the difficulty of the new task. Most likely they reflect a process of consolidation of an already configured task set.
Adolescent↗
Parametric coupling and generalized decoupling revealed by concurrent and successive isometric contractions of distal muscles.
In two experiments we examined the hypothesis of transient parametric coupling during the specification of peak forces of isometric contractions produced by the left and right hand. In the first experiment participants had to produce bimanual contractions with same and different target forces as rapidly as possible in response to an auditory signal; target forces were cued visually with variable cueing intervals. At short cueing intervals reaction times were longer when different peak forces had to be specified than when same peak forces were cued, and this reaction-time difference declined as the cueing interval was increased. Independent of the cueing interval intermanual correlations of peak forces, rise times, and reaction times were smaller in conditions with different peak forces than in those with same peak forces. In the second experiment imperative signals for left-hand and right-hand contractions were separated in time. Target forces for the first response were cued with variable cueing intervals, while for the second response the cues were presented simultaneously with the second imperative signal. Reaction time of the second response was longer when target forces for the two successive responses were different rather than same, and this reaction-time difference declined when the delay of the second signal was increased as well as when the cueing interval for the first response became longer. These results are consistent with the hypothesis of a transient cross-talk between concurrent processes of peak-force specifications; in addition they indicate generalization of the decoupling required to specify different peak forces concurrently to the specification of temporal response characteristics and to processes of response initiation.
Adult↗
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.
Adult↗
Involuntary Rotations of a Steering Device Induced by Voluntary Rotations of the Head and Maintained Eccentric Head Positions.
In a series of 4 experiments, the authors examined involuntary rotations of a steering device (handlebar or wheel) that were associated with periodic head rotations and eccentric head positions. Periodic head rotations resulted in isodirectional involuntary rotations of a horizontally arranged steering device of very small amplitude. When the orientation of a steering wheel was changed to vertical and to a backward tilt, the involuntary rotations were in the opposite direction. That pattern of results is consistent with the assumption that small movements of the shoulder girdle, which are associated with head turns and which cannot be prevented by mechanical immobilization of the shoulder, are propagated to the wheel, but is not consistent with previous suggestions that involuntary rotations of a steering device can result from the action of the tonic neck reflex. Effects that correspond to the pattern of the tonic neck reflex were found only when a spring-centered handlebar was held in an eccentric position; maintenance of the eccentric position was facilitated when the participant's head was turned in the opposite direction. The findings strongly suggest that head movements can result in involuntary movements of a steering device via different mechanisms.
Journal Article↗