Interference in short-term retention of discrete movements.

Although there has been a considerable amount of work on short-term memory for verbal material, little has been done to examine the extent to which the findings applicable to this area can be generalized to non-verbal material. Some work with discrete movements has indicated that, unlike verbal material, there is a rapid, apparently spontaneous decay of a discrete movement over a short interval of time, even when long intertrial intervals are used. It is also found that, although the interpolation of information-processing tasks in the retention interval does not affect the retention of discrete movement, retention is adversely affected by the interpolation of additional motor movements. A series of three experiments examined retroactive interference in the retention of discrete movements, and used this technique to examine the encoding of a discrete movement. The apparatus used for this purpose was a manual lever which could swing in a horizontal plane. The lever could be moved by £, or it could be mechanically driven, moving S/s arm through some predetermined angle. The first experiment involved a retention interval of 9 sec, with three interpolated movements. Effects examined were whether recall over the same path as used during presentation was any better than recall over a different path, whether there were any effects associated with the direction of movement during presentation and recall, and whether there was any significant practice effect in this situation. Results showed a significantly increased absolute error resulting from the interpolated movements, but none of the other manipulations had any effect. In the second experiment, the position of interpolated movements within the retention Interval was examined, as there is an indication in the verbal literature that Interpolated material Is most detrimental when it occurs early in the retention Interval. Results showed a significant tendency for recall to be poorer when material was Interpolated toward« the end of the retention Interval. Possible reasons for this were discussed» and it was concluded that the spontaneous decay effects found with discrete movements were responsible. Similarity effects along the dimension of angle sis« were not found. There was no tendency for recall to be poorer wh«n th« interpolated angle wa« closer in sis« to the target angle, nor for the poorly-recsivled angles to err towards the magnitude of the interpolated angle. In the third experiment, the Interpolated material Involved different components of a complete movement, as it was argued that those components which were most important for the encoding of a movement would produce th« greatest interference. Interpolated material included, (a) preparation of the movement, in which £ began a movement which the apparatus completed for him.