Braking reaching movements: a test of the constant tau-dot strategy under different viewing conditions

Following F. Zaal and R. J. Bootsma (1995), the authors studied whether the decelerative phase of a reaching movement could be modeled as a constant tau-dot strategy resulting in a soft collision with the object. Specifically, they investigated whether that strategy is sustained over different viewing conditions. Participants (N = 11) were required to reach for 15- and 50-mm objects at 2 different distances under 3 conditions in which visual availability of the immediate environment and of the reaching hand were varied. Tau-dot estimates and goodness-of-fit were highly similar across the 3 conditions. Only within-participant variability of tau-dot estimates was increased when environmental cues were removed. That finding suggests that the motor system uses a tau-dot strategy involving the intermodal (i.e., visual, proprioceptive, or both) specification of information to regulate the decelerative phase of reaching under restricted viewing conditions. The authors provide recommendations for improving the derivation of tau;(x) estimates and stress the need for further research on how time-to-contact information is used in the regulation of the dynamics of actions such as reaching.     

Visual information and the control of reaching in children: a comparison between children with and without developmental coordination disorder

Three experiments were performed on reach and grasp in 9- to 10-year-old children (8 controls and 8 with developmental coordination disorder [DCD]). In normal reaching, children in the DCD group were less responsive to the accuracy demands of the task in controlling the transport component of prehension and spent less time in the deceleration phase of hand transport. When vision was removed as movement began, children in the control group spent more time decelerating and reached peak aperture earlier. Children in the DCD group did not do that, although, like the control group, they did increase grip aperture in the dark. When depth cues were reduced and only the target or only the target and hand were visible, children in the control group used target information to maintain the same grip aperture in all conditions, but DCD children behaved as if the target was not visible. Throughout the studies, the control group of 9- to 10-year-olds did not produce adult-like adaptations to reduced vision, suggesting that they had not yet attained adult-like integration of sensory input. Compared with control children, children with DCD did not exhibit increased dependence on vision but showed less recognition of accuracy demands, less adaptation to the removal of vision, and less use of minimal visual information when it was available.     

Abusive interactions and burnout: Examining occupation,gender, and the mediating role of community

Abstract

Two studies examined the association of gender and occupational group (nursing versus non-nursing) with perceived risk of abuse (sexual harassment and verbal and physical abuse) as well as the relationship of perceived abuse risk with burnout and sense of community. Study 1, comprising of two settings (tertiary care hospital, N = 3,062; psychiatric hospital, N = 383), found gender and occupational group associated with perceived risk of abuse (women felt greater risk than men; nurses felt greater risk than non-nurses). It also found a gender/occupational group interaction. Study 2, conducted at an Irish tertiary care hospital (N = 892), found nurses felt at greater risk for all three types of abuse than did non-nurses. Further, women perceived themselves at greater risk for sexual harassment and verbal abuse than did men; the study found no gender difference regarding physical abuse. The analysis identified a gender/occupational group interaction for sexual harassment. The study considers methods of reducing perceived risk in regard to the research literature on abuse at work.     

Discrimination Reversal Conditioning of an Eyeblink Response is Impaired by NMDA Receptor Blockade

In the present study we examined the effects of the specific NMDA receptor antagonist CPP on discrimination reversal learning in rabbits. We report two primary findings. First, the institution of NMDA receptor blockade had no effect on a learned discrimination. Second, after stimulus reversal, CPP treatment impaired acquisition of the discrimination reversal. This impairment manifested itself early in training as a retardation in acquisition of a CR to the new CS+ and late in training as an inability to suppress responsiveness to the new CS-. Given the comparability of the present results with previously published results for phenytoin-treated rabbits, we suggest that the effects of phenytoin on learning in this paradigm is at least in part mediated by its effects on NMDA receptors. We further suggest that these findings emphasize the need to better define the role of NMDA receptor activation and hippocampally-mediated circuits in a variety of associative learning paradigms.     

Selection through Rejection: Reconsidering the Invariant Learning Paradigm

Two experiments are reported that investigate the nature of selections in the McGeorge and Burton (1990) invariant learning paradigm. McGeorge and Burton suggest that subjects implicitly acquire abstract knowledge of an invariant feature (usually the presence of the digit '3') in a set of 30 stimuli. McGeorge and Burton's analysis has recently been challenged by Cock, Berry, and Gaffan (1994) and by Wright and Burton (1995). In this paper, we demonstrate that performance is based on knowledge of other aspects of the learning set besides the invariant digit, but that this knowledge is still implicit. Altering the nature of the learning stimuli to highlight these co-varying features enhances the effects and increases the reporting of explicit knowledge. Our results indicate that performance within this paradigm is more easily characterized as rejection of salient negatives than selection of positive instances, but that salience is not based simply on similarity.     

Private virtues, public detriment: allocating scarce medical resources to the elderly

Churchill reviews Norman Daniels' Am I My Parents' Keeper (Oxford University Press; 1988) and Daniel Callahan's Setting Limits (Simon & Schuster; 1987). Both books present their authors' reflections on one of the most pressing problems of social ethics, how to allocate health care resources to the elderly in a climate of scarcity. Churchill first analyzes Daniels' response to the problem, the "prudential lifespan account," by which health care rights might give persons legitimate claims to services at one stage of their lives but not at another. This approach is contrasted with Callahan's "return to virtue" argument, which rests upon two major claims, one about the appropriate ends of medicine and the other about the meaning of old age. Churchill discusses both works within the context of the problematic relation in the United States between private and public goods, and between individual and social well-being.