Activity of wrist muscles elicited during imposed or voluntary movements about the elbow joint

To examine the coordination of muscles during multijoint movement, we compared the response of wrist muscles to perturbations about the elbow joint with their activation during a volitional elbow movement. The purpose was to test the following two predictions: (a) Responses can occur in muscles not stretched by the perturbation, as has been reported for other multijoint systems; and (b) the motor pattern in response to a perturbation mimics an opposing volitional motor pattern across the two joints. We recorded the electromyographic (EMG) activity of elbow and wrist muscles as well as the flexion/extension motions at the elbow and wrist joints during individual trials that either involved a response to a torque perturbation that extended the elbow or required volitional elbow flexion. The results of this study confirmed that responses were elicited in the nonstretched wrist muscles when the elbow joint was perturbed. The same motor sequence of elbow and wrist flexors was present for both the volitional and perturbation task (with the forearm supinated), regardless of whether the wrist joint was immobilized or freely moving. The findings suggest that the nervous system relies on the purposeful coupling of elbow and wrist flexors to counter the inertial effects during the unrestricted voluntary movement, even though the coupling does not appear to be purposeful during the perturbation or with the wrist immobilized. The coupling of elbow and wrist flexors, however, was not rigidly fixed, as evidenced by muscle onsets that adapted over repeated perturbation trials and a reversal of the wrist muscle activated (wrist extensor) when the forearm was pronated. Hence, the coupling of muscle activities can be modified quantitatively when not beneficial and can be altered qualitatively with different initial configurations of the arm.     

Is object texture a constraint on human prehension?: kinematic evidence

The present experiment determined whether object texture influenced the transport and grasp components of human prehension. Infrared markers placed on the index finger, thumb, and wrist were recorded using a WATSMART system. The test objects were cylindrical dowels (103 mm high, 25 mm diameter, and 150 g in weight) of various surface materials (plain metal, coated with Vaseline, and covered with coarse sandpaper). Only temporal kinematic measures were affected by texture: Movement time (ms), time after peak deceleration (ms), percentages of movement time following maximum aperture, velocity, and deceleration were all significantly greater for the slippery dowel than the normal and rough dowels. Results indicated that the increased time associated with the slippery dowel could be explained entirely by increased time between contact with the dowel and dowel lift. Thus, these results are like those of Weir, MacKenzie, Marteniuk, Cargoe, and Frazer (1991), in which object weight was shown not to affect the free-motion phase, which includes the transport and grasp components of prehension. It appears that intrinsic object properties like weight and texture affect only the finger-object interaction phase of prehension; subsequent research is needed to dissociate inertial and surface friction effects while in contact with objects     

Dynamic role of social support in the link between chronic stress and psychological distress.

How a chronic environmental stressor can interfere with the buffering effects of social support by eroding social support was analyzed in this prospective, longitudinal study. A classic buffering effect of support was found after 2 months of exposure to the stressor, household crowding. Crowded residents with low perceived support had greater increases in psychological distress than did crowded residents with high perceived support. However, after 8 months exposure the buffering effect disappeared. Moreover, greater crowding had become directly associated with lower support, which in turn was associated with greater increases in psychological distress. All analyses controlled for prior distress. Under some types of chronic stress, the buffering effects of social support may be short-lived because the stressor eventually erodes social support.     

An examination of the construct validity of the Social Anhedonia Scale

Two studies bearing on the construct validity of the Social Anhedonia Scale (SA) are reported. Study 1 reported convergent validity coefficients between the SA scale and numerous measures of traits reflecting a generalized attitude toward others (e.g., social interest and empathy) as well as several traits reflecting maladjustment without a social component as a test of discriminant validity (e.g., pessimism and rigidity). Study 1 found impressive convergent validity for the SA scale and mixed discriminant validity. Study 2 found that the SA scale was related to two dimensions of striving for security, one of which is strongly influenced by negative interpersonal tendencies, suggesting support for the validity of the SA scale. Implications for the measurement and concept of social anhedonia are presented.     

Hopelessness in community-residing aged persons: a viable construct?

Previous work with the Geriatric Hopelessness Scale (GHS; Fry, 1984, 1986) suggests that it may be a useful measure of pessimism for a variety of domains among elderly persons. One hundred seven community-residing aged persons were individually administered the GHS and a variety of personality and cognitive functioning measures in an effort to further refine and validate the GHS. Results suggest very modest internal consistency and a poorly defined factor structure for the GHS, in contrast to earlier findings. Although the GHS failed to differentiate elderly persons by age, it was nonetheless related to self-esteem, depression, self-rated health, internality, morale, and life satisfaction. Taken together, these data indicate that the research and clinical utility of the GHS with community-residing aged persons may be more limited than previously believed.     

A multidimensional analysis of internal health locus of control beliefs: separating the wheat from the chaff?

The current study examined the hypotheses that internal health locus of control comprises multiple dimensions and that these dimensions are differentially associated with physical health status. As expected, using covariance structure modeling of data derived from 181 medical outpatients, internal health locus of control was found to be multidimensional. Predicted dimensions included recognition that illness prevention is contingent on successful execution of potential health actions, recognition that illness management is contingent on successful execution of potential health actions, and self-mastery over health outcomes (i.e., the perceived capacity to achieve desired health outcomes). A 4th dimension (i.e., self-blame for negative health outcomes) also emerged. Moreover, as predicted, only perceptions of self-mastery were independently associated with indexes of physical health and well-being.     

Three methods of developing MMPI taxonomies of sexual offenders

In a sample of 261 state hospital sexual offenders, Minnesota Multiphasic Personality Inventory (MMPI) profiles did not differ for offenders with adult victims versus offenders with child victims when offender age was controlled. MMPI 2-point analyses for the whole sample revealed five common codes that were independent of victim maturity. The sample was randomly divided in half and subjected to a cluster-analytic procedure which revealed two MMPI clusters. The first cluster was unelevated, with Scale 4 as its high point. The second cluster had multiple elevations, with Scales 8, 4, 2, and 7 as the highest scales. These clusters were replicated in a cluster analysis of the second half of the sample. However, when the sample was recombined, the two clusters were not externally validated basis on demographic and criminological variables. The results suggest that common psychological variables among sexual offenders may have more discriminative value than victim maturity in developing sexual offender taxonomies.