The stability of precision grip force in older adults

The exceedingly large grip forces that many older adults employ when lifting objects with a precision pinch grip (Cole, 1991) may compensate for a reduced capability to produce a stable isometric force. That is, their grip force may fluctuate enough from moment to moment to yield grip forces that approach the force at which the object would slip from grasp. We examined the within-trial variability of isometric force in old (68-85 years, n = 13) and young (n = 11) human subjects (a) when they were asked to produce a constant pinch force at three target levels (0.49, 2.25, and 10.5 N) with external support of the arm, hand, and force transducer and (b) when they were asked to grasp, lift, and hold a small test object with a precision grip. Pinch force produced in the first task was equally stable across the two subject groups during analysis intervals that lasted 4 s. The elderly subjects produced grip forces when lifting objects that averaged twice as much as those produced by the young subjects. The force variability during the static (hold) phase of the lift for the old subjects was comparable with that used by the young subjects, after adjusting for the difference in grip force. The failure to observe less stable grip force in older adults contradicts a similar recent study. Differences in task (isometric grip force versus isometric abduction torque of a single digit) may account for this conflict, however. Thumb and finger forces for grip are produced through coactivation of many muscles and thus promote smooth force output through temporal summation of twitches. We conclude that peripheral reorganization of muscle in older adults does not yield increased instability of precision grip force and therefore does not contribute directly to increased grip forces in this population. However, force instability may affect other grip configurations (e.g., lateral pinch) or manipulation involving digit abduction or adduction forces.     

A comparison of children who receive and who do not receive permission to participate in research

In a study examining children's social competence in elementary school settings, the authors had the opportunity to compare children who received parental permission to participate to children who did not receive permission. Results indicated that children who were not involved in the study were more likely to be viewed by teachers as having unsatisfactory relationships with peers than children who were in the study. The present results suggest that investigators begin reporting the number of children who do not participate in a given study and begin examining whether minors who receive parental permission differ on important dimensions from minors who do not receive such permission. Ethical considerations of the present study are discussed.     

The Effects of Health Threat Seriousness and Personal Efficacy upon Intentions and Behavior1

Eighty dental patients were pretested with a scale measuring health locus of control and then exposed to a persuasive communication designed to manipulate their beliefs about the seriousness of periodontal disease and their susceptibility to it. The high seriousness condition increased feelings of fear, concern, and threat as well as intentions and reported compliance with recommended oral hygiene procedures. However, patient's perceived personal efficacy in performing the recommended behavior was the most important predictor of subsequent behavior. The implications of the results for Roger's protection motivation theory are discussed.     

Position uncertainty and the perception of apparent movement

Two experiments compared the perception of apparent movement when the second of two successive stimuli always appeared in the same position and when it varied randomly between two spatial positions. The results of both experiments showed that foreknowledge of the position of the second stimulus does not facilitate the perception of apparent movement. Experiment 2 also clearly showed that the space-time relationships of Korte’s third law of apparent movement does not depend on foreknowledge of the position of the second stimulus. These findings imply that apparent movement in real time occurs after the second stimulus has been registered by the visual system. It suggests that apparent movement involves a delayed decision mechanism that stores the first stimulus, the interstimulus temporal interval, and the second stimulus, and then impletes a motion compatible with the stimulus information.     

Legal and ethical duties of the clinician treating a patient who is liable to be impulsively violent

This paper reviews published tort cases that arose after a patient impulsively hurt or killed someone. Plaintiffs alleged breach of the duty to protect (Tarasoff) or negligent release from hospital. There are sixteen cases involving a variety of facts and diagnoses. As a matter of law courts typically hold that impulsive violence is not foreseeable. One jury found a defendant negligent but that verdict was ultimately overturned. Statutes on duty to protect do not imply a duty to act on the fact patterns of impulsive violence in this sample. The author concludes that the ethical duty to do careful clinical work is essentially identical to the legal duty to use due care in these cases. The law imposes no additional burden on the clinician in these cases. © 1998 John Wiley & Sons, Ltd.