What is memory? According to Harvard psychology professor Daniel L. Schacter, memory is a complex entity, comprising multiple systems and processes. It is involved in practically all human actions and defines who one is. It enables humans to learn new skills, to recognize objects, and to recollect events. Memories have the power to make one laugh and make one cry. They are more precious than any material possession, but can be just as fragile. In this comprehensive and well-written study, the author presents twenty years of research on memory by leading researchers, himself included.
Although memory has been compared to a computer, it has been found not to be merely a device for storing and retrieving information. Rather, the act of remembering is a subjective experience in which, as the author writes, memories are records of how one has experienced events rather than replicas of the events themselves. The author likens remembering to a reconstruction of fragments of past experiences.
When one experiences an event, one “encodes” specific details about it, including any meanings or emotions that were associated with it. On a physiological level, the brain records the event by strengthening connections between neurons. Breakthroughs in brain imaging have enabled researchers to understand the functions of the different parts of the brain. The new patterns of connections, the stored fragments of an episode, are called “engrams.” Remembering is not solely dependent on these stored engrams, however. After all, the human brain can contain millions of engrams, which at any one moment lie dormant.
Schacter explains that “awakening” a dormant engram depends on “cues,” or parts of the original experience that a person focused on at the time the experience occurred. The cue and the engram work together to yield the subjective experience of remembering. Cues can take many forms; a cue could be an object, a smell, a taste, a place, or even a photograph. The author uses as an example celebrated French writer Marcel Proust, who noted that it was the taste of a bite of madeleine (a French cookie) dipped in tea that elicited a rush of memories from his childhood, in a famous scene from his À la recherche du temps perdu (1913-1927; Remembrance of Things Past, 1922-1931). Furthermore, Schacter proposes that because recovering any given engram can depend on the right cue, some memories may never be recalled.
Scientists have found that some engrams become more resistant to forgetting over time. In other words, as time passes, short-term memories can be converted, or “consolidated,” into long-term memories. The human brain’s medial temporal lobe is important to memory for a limited period of time after encoding an experience. Over time, memory engrams later become fixed or consolidated in the cortical networks outside the medial temporal region.
Unlike others in his field, the author does not believe that people remember absolutely everything that ever happens to them. There is an element of “natural selection”—one tries to remember what is most important. Most people have also experienced the phenomenon of “automatic pilot,” when one is so preoccupied with other thoughts that one is oblivious to current experiences. According to Schacter, one remembers only what one encodes, and what one encodes depends on who one is. Forgetting is an adaptive feature of one’s memory; one is actually better off forgetting trivial experiences. In fact, it is believed that the brain actively inhibits some thoughts in order better to concentrate on the task at hand.
Memory processes have been divided into three general categories. Semantic memory involves one’s general knowledge of the world and includes conceptual and factual knowledge. It enables one to recognize common objects or understand the rules of a game, for example. Procedural memory enables one to do things, to learn skills and acquire habits. Without procedural memory, one could not ride a bike or hit a home run. Episodic memory allows one to recall personal incidents. Episodic memory is particularly subjective in that it depends solely on the person doing the remembering. Because any given event is filtered through the rememberer’s own memory processes, its remembrance depends on the fragments of the event the rememberer encoded at the time it happened. This concept goes a long way in explaining the many conflicting eyewitness accounts of specific events.
Schacter compares one’s personal recollections to a complex tapestry that includes memories of specific moments and more general recollections of larger periods of time. He divides an individual’s memories into three general categories, arranged hierarchically: lifetime periods, measured in years or decades, such as when one was a teenager; general events, or extended episodes, that are measured in days, weeks, or months, such as a vacation; and event-specific knowledge, measured in seconds, minutes, or hours, such as a wedding. Logically, and as demonstrated by research, memory for lifetime periods and general events is usually better than that for specific events.
Ironically, much of the...