Throwing action from full-cue and motion-only video-models of an arm movement sequence

The purpose of this study was to determine whether videotaped demonstrations of an action which displayed only the motion pattern of a model's limb as compared with one which showed both form and motion provide sufficient information for modelling a given pattern of movement. Video-demonstrations of an arm-movement sequence which ended with a throwing action were shown to adult subjects whose task was to model precisely what they saw. Each demonstration lasted 6 sec. and was shown 6 times. It portrayed the arm of a model, who held a small ball, performing a sequence of movements (flexion and extension of the elbow) which ended in the ball being thrown about 2.5 m with a 'darts-style' action. Three types of demonstration were presented: one showed the whole arm in dark clothing against a light-coloured background, another showed the arm as the relative motion of patches of light situated at the shoulder, elbow, and wrist joints, and the third showed the arm as the relative motion of the upper and lower segments of the arm represented by strips of light-reflectant material. These were the stimuli for the between-groups experimental conditions. Goniometry techniques were used to compare the performance of subjects relative to the model. Analysis showed that the order of the preparatory sequence was correctly produced after 4 trials under all conditions. Range of arm movement in projecting the ball closely approximated that of the model after 4 trials in all conditions. The time taken for the arm to project the ball remained constant across trials under all conditions and was always slower than the demonstrated cadence.(ABSTRACT TRUNCATED AT 250 WORDS)