AP Psychology 2.5: Storing Memories

Four storage processes differ in three ways: duration (how long information lasts), capacity (how much fits) and content (what kind of information is held).

• Sensory memory holds a brief, nearly complete copy of what your senses take in, before you pay attention to any of it. Its capacity is large, but a sight lasts under a second and a sound a few seconds. The content is raw: how something looked or sounded, not what it means.
• Short-term memory holds the few things you are paying attention to, about seven at once by the classic estimate. Without rehearsal they fade within about 20 to 30 seconds.
• Working memory is the workspace where you hold information and work on it at once: adding a bill in your head, or comparing two routes. Its capacity is small; its content is whatever you are using, new or from long-term memory.
• Long-term memory holds knowledge, events and skills for days or a lifetime, with no known limit on capacity. Much of it is stored by meaning, so you keep the gist of a conversation and lose the words.

Short-term and working memory both hold a few things for seconds. The test is what the person does with the information. Only keeping it in mind is short-term memory. Changing it, combining it or calculating with it is working memory. Repeating it under your breath uses working memory's phonological loop, from 2.3, to keep it in short-term storage unchanged.

Information in short-term memory fades fast unless you do something with it. The simplest move is maintenance rehearsal: repeating the information over and over, like saying a gate number to yourself all the way down an airport hallway. While you keep repeating it, it stays. Stop, and it fades on the usual schedule. Maintenance rehearsal prolongs storage, but repetition on its own adds no meaning, so it does much less for keeping information for weeks.

Elaborative rehearsal works with the meaning. You link the new information to something you already know, explain it in your own words, or make up an example of it. To learn that nocturnal means active at night, you might connect it to the owl you hear outside your window, or notice it shares a root with nocturne, a piece of night music. Rehearsing for meaning helps with memory retention: the information is much more likely to still be there next month.

What counts is what you do with the information, not how many times you do it. Reading a definition aloud twenty times is still maintenance rehearsal. Turning it into one example of your own is elaborative.

Autobiographical memory is memory for the events and facts of your own life: your first day at a new school, the street you lived on at age eight, the day a sibling was born. Memories connected to our own lives or selves tend to be more memorable than ones that are not. A new idea you tie to yourself, such as noticing that a trait word in a lesson describes you, has an extra hook to hang on.

A few people go much further. People with highly superior autobiographical memory (HSAM) can be given a date from many years ago and say what weekday it was and what they did, often in vivid detail, for nearly every day since childhood. Their memory for ordinary word lists and school facts is often no better than anyone else's. What is superior is memory for their own lives.

Researchers who compared brain scans of people with HSAM with those of other adults found differences in some brain areas. That may indicate biological processes behind superior memory storage. It is not proof. Only a small number of people with HSAM have been studied, and a brain difference could be a cause of their memory or a result of years spent going over the past.

Storage can be harmed by physical impairment, and it is limited early in development.

Amnesia is a loss of memory, often after a head injury, a stroke or an illness that damages the brain. It runs in two directions, measured from the moment of damage. In retrograde amnesia, memories stored before the damage are lost; a player knocked out in a game may never get back the minutes before the hit. In anterograde amnesia, the person cannot store new long-term memories after the damage. Older memories can be intact, and the person can follow a conversation in short-term memory, but an hour later it is gone. Some people have both.

Alzheimer's disease is a disease, not a single injury. It gradually destroys brain cells, so memory loss grows over years. Recent events usually go first, and older memories later, as the damage spreads.

Infantile amnesia is a developmental limitation, not damage. Most adults remember little or nothing from before about age 3, even though babies and toddlers learn all the time. Experiences from those years are rarely stored in a way that lasts into adulthood.