Formation and decay of sensorimotor and associative memory in object lifting.

The temporal dynamics of the formation and decay of the memory processes underlying the specification of force when lifting objects of either the same or different weight were investigated. Sensorimotor memory enables rapid force programming to the physical object properties. Associative memory may be used to establish a memory link between a colour cue and object weight. In experiment 1, subjects lifted a constant weight in sets of ten lifts 10 s, 5 min, 1 h and 24 h apart. In experiment 2, subjects learned to associate a colour to two different weights to be lifted in alternation within sets of ten lifts 10 s, 5 min, 1 h and 24 h apart. Results of experiment 1 suggest that the memory related to the physical properties of a given object is rapidly established within a few lifts. However, there is a drift of accuracy of force programming that is observed as early as 10 s after the initial set of lifts. Results of experiment 2 imply that people are able to quickly establish an association between visual colour cues and particular object weights. Importantly, the formation of such memory appears to reduce the drift in accuracy observed in experiment 1 and provides the precise programming of grip and lift forces according to the physical object properties for up to 24 h.