Academic journal article Research Quarterly for Exercise and Sport

The Role of Parameter Variability on Retention, Parameter Transfer, and Effector Transfer. (Motor Control and Learning)

Academic journal article Research Quarterly for Exercise and Sport

The Role of Parameter Variability on Retention, Parameter Transfer, and Effector Transfer. (Motor Control and Learning)

Article excerpt

The purpose of this study was to examine the effects of parameter variability on the learning of generalized motor pro grams (GMP) and movement parameterization. Participants attempted to exert a force pattern that resembled in force and time a waveform displayed on a computer monitor. The analysis suggested that relative timing (a measure of the GMP) performance remained remarkably stable across retention and transfer tests, whereby the structure of the movement remained intact, although the parameter or muscle group (effector) changed during transfer. The results also indicated that variable parameter (time) practice did not enhance GMP learning but did degrade the learning parameter that was not varied (force). In addition, parameter specification was substantially less stable than the GMP, with time and force parameter performance deteriorating from the retention to transfer tests. These findings suggest that parameter specification, and not the GMP, is the primary cause of poorer performance in parameter and effect or transfer.

Key words: generalized motor program, movement parameters, parameter learning, variability of practice

Schmidt (1975, 1976, 1982) proposed that a generalized motor program (GMP) is developed over practice and becomes the basis for generating responses within a movement class sharing the same invariant features (e.g., sequencing, relative timing, relative force). Specific movements are produced by the premovement assignment of parameters such as absolute force or absolute time via the recall schema. For example, when the time parameter is varied, the invariant features specified by the GMP are thought to remain intact such that slower movements could be thought of as "stretched-out" (in time) copies of faster movements. Likewise, when the force parameter is manipulated, a movement sequence requiring minimal force could be thought of as a compressed (with respect to force) copy of a more forceful movement.

Schmidt (1975) proposed that the recall schema was essentially a rule governing parameter specification, which was thought to be strengthened as a function of variable practice. This rule was likened to a regression line determined by the relationship between the parameters specified across trials and the resulting movement outcomes such that with each successive data point the relationship was refined and strengthened. This analogy implies that varied response requirements result in a wider range of parameter values being specified during practice, resulting in a wider range of movement outcomes. According to the recall schema proposal, this should enhance formulation of the rule for accurately specifying the parameters (regression line) in the future. The product of a strengthened parameter rule would be more accurate and consistent on retention and especially transfer tests.

The impact of practice variability on the GMP and parameter development, although clearly an important practice variable within the context of schema theory, has not been directly assessed. This is because nearly all experiments investigating variable practice have not partitioned movement errors into separate measures attributable to GMP and parameter errors. Experiments (for exceptions, see Lai & Shea, 1998; Whitacre & Shea, 2000) that have partitioned response errors into GMP and parameter measures have generally used some form of variable practice (i.e., blocked, serial, or random). For example, in the Wulf, Schmidt, & Deubel (1993) experiments, the two groups (63 and 100% KR frequency) in each experiment received the same schedule and range of variable practice. In fact, nearly all knowledge of results (e.g., Wulf, Lee, & Schmidt, 1994; Wulf & Schmidt, 1989, 1994; Wulf et al., 1993) and contextual interference (Sekiya, Magill, & Anderson, 1996; Sekiya, Magill, Sidaway, & Anderson, 1994; Wulf, 1992; Wulf & Lee, 1993) experiments, that have partitioned GMP and parameter errors have used some form of variable practice. …

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