Find in Library

Different mechanisms are involved in the formation of memories necessary for daily living. For example, different memory representations are formed for the practiced transitions between key-presses (i.e. pressing key 2 after 3 in 4-3-2-1) and for the ordinal position of each key-press (i.e. pressing key 2 in the third ordinal position in 4-3-2-1) in a motor sequence. Whether the resulting transition-based and ordinal-based memories (Song & Cohen, in press) can be consciously recalled is unknown. Here, we studied subjects who over a week of training and testing formed transition and ordinal-based memory representations of skill for a 12-item sequence of key-presses. Afterwards, subjects were first asked to recall and type the trained sequence and then to perform random key-presses avoiding the trained sequence. The difference in the ability to purposefully recall and avoid a trained sequence represents conscious recall (Destrebecqz & Cleeremans, 2001). We report that (a) the difference in the ability to purposefully recall and to avoid the trained sequence correlated with ordinal-based but not with transition-based memory, (b) subjects with no ability to recall or avoid the trained sequence formed transition-based but not ordinal-based memories, and (c) subjects with full ability to recall and avoid the trained sequence formed both transition-based and ordinal-based memories. We conclude that ordinal-based memory can be voluntarily recalled when transition-based memory cannot, documenting a differential capacity to recall memories forming a motor skill. Understanding that different memories form a motor skill, with different neural substrates (Cohen & Squire, 1980), may help develop novel training strategies in neurorehabilitation of patients with brain lesions.