Like riding a bicycle

Everyone has to rely on muscle memory for daily function.  From typing on a computer keyboard to playing a musical instrument, motor memory clears your consciousness to allow for a higher level of performance.  As a motor task is repeated it becomes stored as motor memory so that less effort is required the next time you want to complete that same task.  This prevents the fingers from interfering with a musician’s expression or a typist’s thoughts.  Research investigating motor memory has revealed that the process of storing this information is actually the product of both long and short term memory.

Short term memory is finite, so it gets erased periodically to make room for other memories.  To maintain motor memory it must become a part of long term memory, which is more stable and theoretically infinite.  A simple motor task requires less memory to perform.  For example, knitting is a simple motor task involving looping yarn in a particular pattern.  This motor function may not require you to engage your long term memory because the task is simple enough to be handled by short term memory.  Therefore, it is easier for you to forget how to knit after you stop practicing. 

This can be contrasted to a more complex motor task, such as playing a wind instrument.  This task requires a combination of more complex physical motor skills.  To produce the correct notes, the musician must coordinate supportive breathing, correct finger technique, good posture, accurate tonguing, and a firm embouchure on the mouthpiece.  Engaging in multiple motor tasks requires the use of long term memory because of complexity.  Trying to learn all of these motor skills at once will take longer than learning to knit, but will make it harder for the musician to forget how to play his instrument.

This phenomenon is known as the contextual interference effect.  The mechanism behind this effect was uncovered while studying stroke patients.  These patients had short term memory damage, causing them to rely more on their long term memory.  In a visual-spatial test, post-stroke patients had a longer retention than non-stroke patients.  This occurred even in conditions that would normally promote the use of short term memory. 

Not only is this information useful for someone looking to learn a new skill, but also may help rehabilitate stroke patients.  Learning two motor tasks at once may take longer to master, but may increase memory retention.