From the moment of birth, each of us is exposed to a world full of sensations and information. All of these experiences – first kisses, soft summer breezes, 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 autobiographical memory presents a problem.
Many other kinds of memory are tested in the laboratory using experiments planned out in painstaking detail. That doesn't work so well for autobiographical "episodic" memories, which are made over time and everywhere along the way.
The 19th century English psychologist Sir Francis Galton pioneered a simple method to study autobiographical memory, a modified version of which is still used today. 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 try and catch his recollections.
One of Galton's findings was that it was difficult to pinpoint when the events he remembered had occurred. Another was that his brain often produced 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 modified Galton's cue word method and used it 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, supporting the "power law of forgetting." The law, based on numerous studies of other types of memory, predicts that most information will be forgotten shortly after being learned. In fact, a graph of the relationship between forgetting and time would resemble a steep slide. The rate of forgetting does level off eventually, according to the law, leaving a small but stable core of knowledge.
As life expectancy continued to increase and interest in understanding age-related changes in cognition grew, psychologists began studying autobiographical memories reported by middle aged and older people. Imagine their surprise when, instead of a steep slide, what they found was something that resembled a bumpy roller coaster.
The roller coaster began with a five-year period of "childhood amnesia," during which few autobiographical memories were reported, and ended with a sharp incline of memories, corresponding to the most recent past.
What wasn't expected was the sizable "bump" of memories from adolescence and young adulthood. And that unlike many other kinds of memory, which change with age, the availability of large numbers of memories from the bump years appears to remain constant for healthy adults into their 90s.
Researchers would like to explain the "bump," but haven't been able to agree on what accounts for it. One discredited theory says the bump, or "reminiscence effect," simply reflects brain functioning, that the reason so many memories are recalled from these years is because that's when the brain is working best. Another says it's because many events are new and exciting to people when they are so young, and because there's less chance for other, similar experiences to interfere with how well things are learned or remembered. A third theory suggests that people establish a narrative about who they are based on experiences in their teens and twenties, and that fewer new memories need to be incorporated into that narrative once their identity has been established.
What's clear is that we have many reasons for remembering our past.
Sometimes we intentionally reminisce, for example when we want to share old stories with friends and family. The retelling of the past in social settings is an intricate dance taught to children early in life.
Some events are so surprising and important that they become flashbulb memories. For example, many people can remember exactly where they were when they heard the news John F. Kennedy was shot, that man had set foot on the moon, or that airplanes hit the World Trade Center.
On other occasions the memories pop up out of the blue, summoned by something as fleeting as a familiar feeling. "(T)he smell and taste of things remain poised a long time, like souls, ready to remind us," is how the French novelist Marcel Proust described it.
Studies have also shown that autobiographical memories aren't necessarily accurate, that they are creative constructions that may change over time to keep up with new circumstances. And that illness or trauma can affect the ability to recall who participated in remembered events, the details of the events, and the life periods in which they occurred.
Do you wonder if you have a memory "bump"? Click here to find out.