Sleep is just one of the factors affecting our memory. Memory can be defined as the set of systems for projecting information into the future. As Schmidt and Bjork (1992) point out, "the objective of learning in real life must be to maximize future performance and transfer to new situations. [...] Teachers often believe that factors that maximize performance and learning speed during training achieve both these goals. However, a whole series of experiments indicate that this assumption is often false." In other words, teachers and students are sometimes radically mistaken about the conditions that optimize memory.
As early as 1885, Ebbinghaus hypothesized that forgetting follows an exponential law as a function of time. However, the speed of this decrease and its asymptote seem to vary according to conditions. What factors determine forgetting? The first essential factor is the depth of stimulus processing: for a constant duration of exposure, the same words will be better retained if they have undergone deep semantic processing rather than superficial judgment. Making the effort to understand a word or phrase facilitates its later recall. Henry Roediger and his colleagues elevate this result to the status of a principle: "Making learning conditions more difficult, which requires students to make a greater commitment and cognitive effort, often leads to better retention." (Zaromb, Karpicke and Roediger, 2010).
