Walter E. Davis

Body-scaled ratio as a control parameter for prehension in 5- to 9-year-old children.

The purpose of the experiment was threefold: (a) To find evidence that grasping is body-scaled and thus remains invariant during development; (b) to seek evidence that the body-scaled ratio of cube and hand size serves as a control parameter for the phase transition from one-handed to two-handed grasping by identifying the presence of sudden jump, enhanced variance, multistability, and hysteresis; and (c) to examine whether the stability properties of the observed grasping patterns increase with age. Thirty-three children aged 5, 7, and 9 years old were required to grasp and lift 14 cardboard cubes of different sizes (2.2, 3.2, 4.2, etc. to 16.2 cm diameter). Three conditions were used: (a) an increasing condition with sizes ordered from the smallest size to the largest; (b) a decreasing condition, with the sizes ordered from the largest to the smallest; and (c) twice in a different random order. Video recordings were analyzed and scored for the percentage of one-handed grasps. The results showed that the shift from one-handed to two-handed grasping occurred at the same body-scale ratio between cube size and finger span for all three age groups. Evidence was found for the presence of a sudden jump, enhanced variance, multistability, and hysteresis, indicating that the body-scaled ratio of cube and hand size serves as a control parameter. No change with age for the stability properties of the grasping patterns were observed.

Ecological task analysis utilizing intrinsic measures in research and practice

Abstract Ecological task analysis (ETA) originally was proposed by Davis and Burton in 1991 to facilitate the linking between basic and applied research and theory and application in the area of adapted physical education. There, four steps in an applied model were laid out based upon theory and research. In the present paper, additional empirical and theoretical work, including social referencing studies, which supports the key concepts of ETA are included, targeting a broader audience of persons in a variety of movement therapy and physical activity instruction professions. Following this expanded overview, the concept of using intrinsic measures to assess movement performance is addressed in detail, including applications of dimensional analysis, allometric procedures, and Froude numbers. These performer-scaled measures are offered as an important way to establish direct links between task goals and the constraints of the performer and the environment, one of the four guiding concepts of ecological task analysis.

Muscle Stiffness in Down Syndrome and Other Mentally Handicapped Subjects: A Research Note

An attempt was made to determine the effects of strength training on elbow flexor stiffness of Down syndrome, non-Down syndrome mentally handicapped, and nonhandicapped subjects. It was hypothesized that stiffness would be affected by the training. Results showed that only half of the individual subjects increased their maximum voluntary contraction (MVC) level as a result of the training and that premeasures and postmeasures of MVC were not significantly different for any of the three groups. As expected, for both premeasures and postmeasures, nonhandicapped subjects had a significantly higher MVC than the other groups who were not significantly different. An important finding was that measures of stiffness (slopes of the IEMG × Torque) were not significantly different for the three groups. This finding is consistant with recent studies (Davis & Kelso, 1982; Shumway-Cook & Woollacott, in press) but raises serious doubts about the popularly held opinion that Down syndrome individuals are hypotonic. It was also found that both the Down syndrome and other mentally handicapped subjects produced significantly less torque at the maximum level than the nonhandicapped subjects. These findings suggest that deficits in mentally handicapping conditions result from a decrease in the range of a primary motor control parameter λ (see Feldman, 1986).