From remembering phone numbers to directions, we rely on working memory to hold small bits of information for short periods of time. While working memory has generally been extensively studied, few papers have focused on a form of working memory called motor working memory (MWM), which helps us remember recent movements. Recently, however, a team of Yale psychologists, including Hanna Hillman and professor Samuel McDougle, explored how movements are represented in MWM.
The researchers hypothesized that humans store two different types of information in MWM: limb-dependent information, which is tied to a specific limb, and limb-independent information, which can be generalized across multiple limbs. “[You might] remember how it felt to do the movements at a certain angle, or you think about where you move—like the trajectory through space or the end position,” Hillman said.
To distinguish between these two scenarios, the researchers enlisted the help of a robot. Hillman used a robotic arm to teach the participants a series of reaching movements and then asked them to recall the sequences. Half of the participants were asked to repeat the movement with the same arm. However, the other half switched hands during the recall phase, preventing the participants from using limb-dependent information. It turned out that participants had poorer recall when they switched hands, but only for recently encoded movements. Earlier movements were equally well-remembered regardless of which hand they recalled it with, suggesting that limb-independent information is more robust than limb-specific information.
Hillman’s research provides key insights into the inner workings of memory, which has the potential to revolutionize rehabilitation therapy. After someone has a stroke or traumatic brain injury, they must relearn motor skills. One day, our understanding of the foundations of MWM might help us design medical technologies to help patients recover from these conditions.
Image courtesy of Flickr.