Repetition Effects in Grasping

The task in the present experiments was to reach out and grasp a novel object that afforded two possible grips. Different versions of the object were created that biased subjects to use one grip or the other. The dependent variable was the repetition effect, the tendency to repeat the grip that was used on the previous trial. In Experiment I, two qualitatively different objects were used, and it was found that the repetition effect was specific to the object being grasped: There was much less tendency to use the same grip as the previous trial if the object being grasped was different. Moreover, the effect lasted over intervening trials and was even present with more than five intervening trials. In Experiment 2, the global context was manipulated, so that in some blocks one grip was much more likely than the other. However, this manipulation had little effect on the choice of grip and did not interact with the repetition effect. In Experiment 3, the hand used to grasp the object was manipulated, and there was little change in the repetition effect. Thus, a grip was more likely to be used if it was used on the previous trial, regardless of whether the previous grasp was performed with the left or right hand. In Experiment 4, a similar result was found for a manipulation of object location and orientation. Our interpretation of these results is that subjects prepare for an action by retrieving action features from memory, and that the object to be grasped provides a critical cue for that memory retrieval. In this view, the repetition effect is essentially a memory recency effect.