Decay and interference effects in the short-term retention of a discrete motor act.

Abstract

The short-term retention of force responses was measured. The dependent variables were the absolute and algebraic errors made by S in attempting to reproduce a criterion force during recall trials. In Exp. I, retention was measured over five unfilled intervals ranging 4-60 sec. Forgetting, i.e., an increase in errors, was not found. Experiment II was a partial replication of Exp. I, with the addition that during half of the retention intervals, 5 was required to count backwards. The result was a decrease in error over a 30-sec. retention interval for both filled and unfilled conditions. Significantly larger errors were associated with the filled condition. In Exp. Ill, the recall response was found to be shifted in the direction of the relative magnitude of an interpolated force to the criterion force. Also, the increase in error associated with filled retention intervals was successfully replicated. For Exp. IV, successive repetitions of the criterion force prior to the recall trial were found to produce an increase, not decrease, in error at recall. All four experiments were characterized by overshooting response sets (positive algebraic errors) at recall. Detailed comparisons with available data from earlier motor short-term memory (STM) studies indicated that the latter were characterized by undershooting response sets at recall but that there was a set of consistent findings across the earlier studies and the present one, though apparent differences in memory functions were obtained. Consistencies were with respect to the directional shifts occurring in the algebraic error scores as a function of various independent variables. The different memory functions were then related to the interactions of the different response sets with these algebraic error shifts. A dual process theory of motor STM, incorporating decay and interference features, is advanced to account for the set of findings, and similarities with dual process theories of verbal STM are noted.