If you are learning a skill such as playing the piano, you have to master the fact-based aspect (the sequence of notes) and also the movement-related aspect (moving your fingers in the correct way on the keys). Both aspects improve during practice, but only one continues to improve afterwards, as what you’ve learned is consolidated in your brain. Now researchers have found that which aspect this is depends on whether it’s night or day.
Daniel Cohen and colleagues at Harvard Medical School investigated these two aspects of learning by asking 50 participants to learn a sequence of key presses with their right hand. They then asked the participants to switch hands. For some of the participants the key sequence stayed the same but because they were now using a different hand, they obviously had to learn a different order of finger movements (see Figure). For the other participants, the sequence was mirror-reversed so they obviously had to learn a new sequence, but because they had switched hands, the order of the finger movements was actually same (see Figure). This procedure allowed the researchers to disentangle the fact-based and movement-based aspects of learning a motor skill. Some of the participants completed this initial part of the experiment in the morning, others in the evening.
Twelve hours later the participants were tested again. Of those participants who had to learn new finger movements, only those originally tested in the morning showed evidence of improvement. By contrast, of those who had to learn a new key-press sequence, only those who were previously tested in the evening and had therefore since slept, showed any sign of improvement.
The researchers said “We found that goal-based [i.e. fact-based] improvements developed exclusively overnight, whereas movement-based improvements developed exclusively over the day”.
“This deepens our understanding of [skill] consolidation by showing that off-line skill enhancement depends on multiple distinct processes that are preferentially engaged depending on when consolidation takes place”, they concluded.
Cohen, D.A., Leone, A-P., Press, D.Z. & Robertson, E.M. (2005). Off-line learning of motor skill memory: A double dissociation of goal and movement. In Press, DOI: 10.1073/pnas.0506072102.
Link to related review article