The retention of motor skills, now referred to as muscle memory, also began to be of great interest in the early 1900s. Most motor skills are thought to be acquired through practice; however, mere observation of the skill has led to learning as well. Research suggests we do not start off with a blank slate with regard to motor memory although we do learn most of our motor memory repertoire during our lifetime. Movements such as facial expressions, which are thought to be learned, can actually be observed in children who are blind; thus there is some evidence for motor memory being genetically pre-wired.
In the early stages of empirical research of motor memory Edward Thorndike, a leading pioneer in the study of motor memory, was among the first to acknowledge learning can occur without conscious awareness. One of the earliest and most notable studies regarding the retention of motor skills was by Hill, Rejall, and Thorndike, who showed savings in relearning typing skills after a 25 year period with no practice. Findings related to the retention of learned motor skills have been continuously replicated in studies, suggesting that through subsequent practice, motor learning is stored in the brain as memory. This is why performing skills such as riding a bike or driving a car are effortlessly and 'unconsciously' executed, even if someone had not performed these skills in a long period of time.