Visual demonstration and movement production: effects of timing variations in a model's action.

The purpose of this study was to determine whether movement production during modelling would register timing changes communicated by a model during video-demonstration of a throwing action. 60 boys, 12 yr. of age, were placed in three groups and observed a computer-simulated, point-light demonstration of a darts-style movement used by a model to project a lightweight ball about 2.5 m in a forward direction. Only the relative motion of model's wrist, elbow, and shoulder were displayed. First, subjects were required to identify the action. Immediate response was 88% for the fastest demonstration (model's natural cadence with a wrist velocity of 3.5 rad./sec.), 81% (1.45 rad./sec.), and 65% (0.92 rad./sec.). Second, 3 subjects (1 from each of the original groups) modelled the action when the directional change of the model's arm and its spatial arrangement were held constant but the timing of traverse of the arm was randomly varied (3 levels). Analysis showed that all subjects produced the correct sequence of movement. There were no differences in production of the spatial parameters of the demonstrations but significant differences in the modelling of the timing parameters. These findings are related to the use of visual demonstrations during motor skill instruction and, particularly, the communication of specific aspects of an action.