A new approach to task analysis is presented based upon an ecological theory of perception and current motor development and control theories. The ecological task analysis (ETA) approach stands in sharp contrast to more traditional approaches and offers procedures equally applicable to instruction and assessment of movement performance as well as to applied research. The strengths of the ETA approach lie in (a) its grounding in current motor development and control theories, (b) its linking of the task requirements, environmental conditions, and performer characteristics, (c) its application of a functional and dynamic approach to instruction and assessment, and (d) its integration of instruction and assessment procedures. Following a discussion of the traditional approach and ecological theory, four concepts are presented that emanate from Gibson’s theory of affordances. From these concepts ETA procedures are derived. Applied research questions relating to task analysis are also implied from the ecological approach and are presented in the final section.

Following Asatryan and Fei'dman (1965), two experiments were conducted to describe the so-called invariant mechanical properties underlying movement control in Down's syndrome and normal subjects. The invariant characteristic is a curve on a graph of joint torque versus joint angle. The task required subjects to maintain a steady joint angle against an external load (torque). Torque was systematically changed via partial unloading in order to obtain torque by length (joint angle) functions at three separate initial joint angles. Instructions required subjects "not to intervene" when unloading occurred in Experiment 1 and to "tense" their muscles prior to unloading in Experiment 2. Both normal and Down's syndrome groups revealed systematic torque by length functions that might be expected according to a simple mass-spring system model. Although the gross organization of movement in Down's syndrome subjects was nearly the same as normals, important differences between the two groups were found. Down's syndrome subjects revealed underdamped motions relative to normals (as shown by differences in the degree of oscillation about the final equilibrium position) and were less able to regulate stiffness (as shown by differences in slope of the torque by angle functions in Experiment 2). We promote the notion that damping and stiffness may be sensitive indices of hypotonia-the most common description of neuromuscular deficiency in Down's syndrome

The purpose of the experiment was threefold: (a) To find evidence that grasping is body-scaled and thus remains invariant during development; (b) to

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).

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A fractionation technique was employed to determine the locus of reaction time delay in Down syndrome (DS) and other adult subjects with mental retardation (MH). Twenty-three subjects (8 nondisabled, 8 MH, and 7 DS) responded to a light, sound, and combination light/sound signal. Dependent measures of premotor time, motor time, total reaction time, and movement time were obtained during a 20° elbow extension movement and were analyzed separately. As expected, both MH and DS subjects were slower and more variable in their responses than the subjects without disabilities. In turn, DS subjects were significantly slower but not more variable than the MH subjects. There were no significant differences between the DS and MH subjects on movement times. Evidence for both a specific (premotor) and a generalized (both premotor and motor) locus of delay was found. Some difference in signal effect was also found for the DS subjects.

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