From the moment of birth, each of us is exposed to a world full of sensations and information. All of these experiences — first kisses, familiar places, sad farewells — have the potential to end up as autobiographical memories.
Not all of them do, of course. Scientists have long been interested in understanding what we remember about our past and why we remember it. But figuring out a way to study this presents problems. Other kinds of memory are tested fairly easily in the laboratory by way of experiments in which people are asked to do things like memorize lists of related and unrelated words. But this approach doesn't work so well for autobiographical memories, which are acquired over time and in various places along the way.
The 19th-century English psychologist Sir Francis Galton pioneered a simple method to study autobiographical memory. He decided to go fishing, as it were, for memories associated with a list of common, everyday words. Four times he threw out his net of words, using the same cues to catch his recollections.
One of Galton's findings was that it was difficult to pinpoint when the events he remembered had occurred. Another finding was that his brain tended to pull up the same associations over and over again. "This shows much less variety in the mental stock of ideas than I had expected," he wrote, "and makes us feel that the roadways of our minds are worn into very deep ruts."
In the 1970s, researchers adapted Galton's cue-word method to study the distribution of autobiographical memories over time. They found that the college students they tested reported many more memories from the recent than the distant past. In fact, researchers found that a graph of the relationship between forgetting and time resembles a steep slide. Still, over time, the rate at which one forgets things does level off, leaving us with small but stable cores of knowledge.
As life expectancy increased, psychologists began studying autobiographical memories reported by middle-aged and older people. Imagine their surprise when, instead of encountering a simple slide, they found something resembling a bumpy roller coaster track, with a pronounced "bump" of memories from adolescence and young adulthood. Researchers haven't yet agreed on the causes of this "bump." One (now discredited) theory says the bump, or "reminiscence effect," simply reflects the fact that the brain functions best during adolescence and young adulthood.
Another theory: Many situations are new to younger people, so memories from this time are more durable because they were laid down without significant interference from other, similar experiences.