In his great novel Remembrance of Things Past or In Search of Lost Time, Marcel Proust explored what are called "involuntary memories" - those that come to us quite suddenly without conscious effort, usually triggered by one of the senses. The fact that his book has two titles in English might suggest there is some doubt as to how our minds go about remembering things. In perhaps the most well-known such episode in the novel, the character Marcel is reminded of his childhood by the aroma produced when dunking a cake in a cup of tea. This is not far away from the belief that as we get older we can remember quite clearly incidents from years ago, but find it hard to remember what we did last week. Proust's insight into memory is certainly true of one way the mind works. But why and how do we remember what we do?
Experts believe that we store memories in three ways. First, there is the sensory stage which is to do with perception and lasts only a fraction of a second, taking in sight, sound, touch, and so on. These first perceptions and sensations are then stored in the short-term memory, which is the second stage. Finally, important information or information that has been reinforced by, for example, repetition, is then filtered into the long-term memory. Naturally, we tend to more easily absorb material on things we already know something about.