Force and Directional Force Modulation Effects on Accuracy and Variability in Low-Level Pinch Force Tracking

The authors investigated how varying the required low-level forces and the direction of force change affect accuracy and variability of force production in a cyclic isometric pinch force tracking task. Eighteen healthy right-handed adult volunteers performed the tracking task over 3 different force ranges. Root mean square error and coefficient of variation were higher at lower force levels and during minimum reversals compared with maximum reversals. Overall, the thumb showed greater root mean square error and coefficient of variation scores than did the index finger during maximum reversals, but not during minimum reversals. The observed impaired performance during minimum reversals might originate from history-dependent mechanisms of force production and highly coupled 2-digit performance.     

Regret and Responsibility Resolved? Evaluating Ordóñez and Connolly's (2000) Conclusions

T. Connolly, L. D. Ordo;aan;atez, and R. Coughlan (1997, Organizational Behavior and Human Decision Processes, 70, 73-85) argued, on the basis of 5 experiments, that regret need not be related to a sense of responsibility for the regretted outcome. We (M. Zeelenberg, W. W. van Dijk, & A. S. R. Manstead, 1998, Organizational Behavior and Human Decision Processes, 74, 254-272) showed in 2 experiments that this conclusion was premature, because it was based on an indirect measure of regret (i.e., overall happiness with the decision outcome). When regret was directly measured, the predicted effects of responsibility were found. L. D. Ordo;aan;atez and T. Connolly (2000, Organizational Behavior and Human Decision Processes, 81, 132-142) replicated our findings in 2 experiments. Based on their findings they arrived at 4 conclusions. In this rejoinder we first discuss Ordó?ez and Connolly's new studies and we then discuss the validity of their 4 conclusions. Copyright 2000 Academic Press.     

Initiation of Bilateral Responses in a Kinesthetic Reaction Time Task

Two experiments are presented in which different mechanisms controlling each limb in a bilateral arm response to a unilateral kinesthetic stimulus are postulated to occur. In Experiment 1, the limb serving as the stimulus limb was described as operating with relative invariance by using a tightly coupled input-output reflexive pathway, whereas the nonstimulus limb appeared to be controlled by higher-order processing thought to be more susceptible to influences such as hemispheric specialization and stimulus expectancy. The differential control model was further tested in Experiment 2 by retaining the intrahemispheric pathway of the unilateral kinesthetic stimulus but experimentally uncoupling the reflex mechanism from the stimulus side. Analyses of bilateral EMG premotor latencies under these conditions revealed that each response side can be controlled at separate levels —i.e., by a reflexive type mechanism or by higher-order processing when one of the response limbs is also the stimulus limb. When the stimulus is on the same side but not generated by either responding limb, both sides reflect behavior that is best described by an information processing type of voluntary control.     

Quantification of manual force control and tremor

Isometric impulse frequencies associated with active tremor and force regulation were examined in 10 patients with idiopathic Parkinson's disease (PD) and in 10 older adults (OAs) who performed an isometric tracing task. The authors decoupled and analyzed the data to determine whether PD-related tremor in the thumb and in the index finger during isometric force control are related and whether PD impairs the performance of volitional force control beyond the errors contributed by tremor. After decoupling, there were clear and robust differences in PD patients' control of isometric force that could not be attributed to action-tremor error. Those errors, which occurred in the absence of movement, suggest impairment in coordinated recruitment and derecruitment of motor units during a fine-motor task.     

Initiation of bilateral responses in a kinesthetic reaction time task

Two experiments are presented in which different mechanisms controlling each limb in a bilateral arm response to a unilateral kinesthetic stimulus are postulated to occur. In Experiment 1, the limb serving as the stimulus are postulated to occur. In Experiment 1, the limb serving as the stimulus limb was described as operating with relative invariance by using a tightly coupled input-output reflexive pathway, whereas the nonstimulus limb appeared to be controlled by higher-order processing thought to be more susceptible to influences such as hemispheric specialization and stimulus expectancy. The differential control model was further tested in Experiment 2 by retaining the interhemispheric pathway of the unilateral kinesthetic stimulus but experimentally uncoupling the reflex mechanism from the stimulus side. Analyses of bilateral EMG premotor latencies under these conditions revealed that each response side can be controlled at separate levels-i.e., by a reflexive type mechanism or by higher-order processing when one of the response limbs is also the stimulus limb, both sides reflect behavior that is best described by an information processing type of voluntary control.