Validation of a full body 3-D dynamic linked segment model

In studies related to human movement, linked segment models (LSM's) are often used to quantify forces and torques, generated in body joints. Some LSM's represent only a few body segments. Others, for instance used in studies on the control of whole body movements, include all body segments. As a consequence of the complexity of 3-dimensional (3-D) analyses, most LSM's are restricted to one plane of motion. However, in asymmetric movements this may result in a loss of relevant information. The aim of the current study was to develop and validate a 3-D LSM including all body segments. Braces with markers, attached to all body segments, were used to record the body movements. The validation of the model was accomplished by comparing the measured with the estimated ground reaction force and by comparing the torques at the lumbo-sacral joint that resulted from a bottom-up and a top-down mechanical analysis. For both comparisons, reasonable to good agreement was found. Sources of error that could not be analysed this way, were subjected to an additional sensitivity analysis. It was concluded that the internal validity of the current model is quite satisfactory.     

On optimal smoothing and derivative estimation from noisy displacement data in biomechanics

Estimating derivatives from noisy displacement data is a notoriously ill-posed problem in signal processing and biomechanics. Following the work of Wood and Jennings (1978) and Hatze (1979, 1981), the present paper describes the use of optimally regularized, natural quintic splines for estimating smoothed positions, velocities, and accelerations from equidistantly sampled, noisy position measurements. It appears that the nature of the boundary conditions of the data is of some importance, since various algorithms used hitherto result in artefacts throughout the data if the true derivatives at the record ends differ significantly from zero. Natural quintic splines do not suffer from this disadvantage below the third derivative.The ill-posed character of movement analysis has some interesting implications for movement synthesis and optimization, similar to the indeterminacy of muscular co-contraction from merely external, biomechanical measurements.     

The web of work for technical and managerial employees

This study examines aspects of the job and off-job lives of technical and managerial employees. A framework for studying parallel dimensions in these two life spheres is developed. Variables include alienation—powerlessness and meaninglessness—and activities—variety, control, social interaction, and purpose. Findings show strong interaction between alienation from work and that experienced from life off the job. Limited relationships between activity dimensions were found. Overall, results suggest that employees' feelings of alienation carry over strongly between the two life spheres but that only limited carry-over occurs between job activities and those away from work. Findings give no support to the compensatory view of relationships between employees' job and off-job lives.     

Involuntary memory and the development of retrieval skills in young children

An incidental memory paradigm was used to study involuntary encoding processes and voluntary retrieval strategies in children's memory. Preschool (mean age: 4 years, 4 months) and kindergarten (mean age: 5 years, 10 months) children sorted pictures according to their color or category membership, and then received either a recall test (Experiment 1) or a recognition test (Experiment 2). Better retention of category- than color-sorted items was observed for kindergarten children in free recall, preschool and kindergarten children in cued recall, and neither group in recognition. These results were interpreted in terms of the retrieval strategies used by children in each of the memory tasks. The importance of distinguishing between voluntary and involuntary memory processes, and between acquisition and retrieval, in studies of depth-of-processing was emphasized. Developmental differences in performance appear to derive primarily from the role of voluntary search strategies in retrieval, rather than from age differences in involuntary encoding processes.     

Tokens for stuttering

Four young stutterers were observed during 10 weekly sessions. Each session was divided into pretreatment, treatment, and posttreatment segments. Redeemable tokens were administered contingent upon stuttering behaviors in the treatment segment of the Experimental condition. In a Parallel Control condition, no tokens were administered during the entire session. The differences between the pretreatment and treatment segments were compared for the two conditions. Three subjects had dramatically fewer stuttering behaviors when tokens were being administered, while the fourth had more stuttering under the same condition. The subject whose stuttering increased had a history of therapy in which voluntary, “faked” stuttering had been called for, and the behaviors that increased were judged to be of this type. The decreases were interpreted as suggesting that the contingent tokens acted to countercondition the aversiveness of the stuttering experience, which reduced the anticipation of stuttering and hence the stuttering itself. The increase was felt to be simple reinforcement. The counterconditioning interpretation was borne out in two clinical applications in which money was presented contingent on stuttering behaviors judged to be aversive to the stutterer, and in which dramatically sudden, but long-lasting, improvement was seen.     

Communicative stress and stuttering frequency during normal,whispered, and articulation-without-phonation speech modes

The effect of communicative stress on the frequency of stuttered syllables in 12 adult stutterers reading six different but equivalent passages using normal voicing, whispering, and articulation-without-phonation speech under a stress and a non-stress condition was studied. Although the frequency of stuttering was significantly greater in the normal voicing mode than in the whispering mode and greater in the whispering mode than in the articulation-without-phonation mode, no differences were found between the stress and the nonstress conditions with respect to stuttering.