CHAPTER 9
Memory
Theme: Memory is not like a tape recorder or a video camera: Memories change as they are stored and retrieved.
Preview
“What the Hell’s Going on Here?”
It’s February and Steven is cross-country skiing on the ice of Lake Michigan. He stops for a moment but quickly realizes that he is very cold. Steven decides to turn back. In a few minutes comes a new realization: He is lost. Wandering on the ice, he grows numb and very, very tired.
Put yourself in Steven’s shoes, and you will appreciate the shock of what happened next. Steven clearly recalls wandering lost and alone on the ice. Immediately after that, he remembers waking up in a field. But as he looked around, Steven knew something was wrong. It was spring!
The backpack beside him contained running shoes, swimming goggles, and a pair of glasses—all unfamiliar.
As he looked at his clothing—also unfamiliar—Steven thought to himself, “What the hell’s going on here?” Fourteen months had passed since he left to go skiing (Loftus, 1980). How did he get to the field? Steven couldn’t say. He had lost over a year of his life to total amnesia.
As Steven’s amnesia vividly shows, life without memory would be meaningless. Imagine the terror and confusion of having all of your memories wiped out. You would have no identity, no knowledge, no life history, no recognition of friends or family. Your past would be a total blank. In a very real sense, we are our memories.
This chapter discusses memory and forgetting. You’ll almost certainly discover ways to improve your memory in the information that follows.
¡ Remembering is an active process. Memories are frequently lost, altered, revised, or distorted.
¡ Different strategies are required to make the best use of short-term memory and long-term memory.
¡ Remembering is not an all-or-nothing process. Information that appears to be lost may still reside in memory.
¡ An inability to retrieve information isn’t the only cause of forgetting. Often, memory failures occur because information wasn’t stored in the first place.
¡ Extreme caution is warranted when “recovered ”memories are the only basis for believing that a person was sexually abused during childhood.
¡ Although it’s true that some people have naturally superior memories, everyone can learn to improve his or her memory.
¡ Memory systems (mnemonics) greatly improve immediate memory. However, conventional learning tends to create the most lasting memories.
¡ Limitations of memory that sometimes appear to be flaws are actually adaptive and desirable in most circumstances.
Gateways to Memory
Is there more than one type of memory?
What are the features of each type of memory?
Is there more than one type of long-term memory?
How is memory measured?
What are “photographic” memories?
What causes forgetting?
How accurate are everyday memories?
What happens in the brain when memories are formed?
How can memory be improved?
How has evolution shaped human memory?
Key Questions
Stages of Memory—Do You Have a Mind Like a Steel Trap? Or a Sieve?
Do you remember what you had for breakfast this morning? Or what happened on September 11, 2001? Of course you do. But how is it possible for us to so easily travel back in time? Let’s begin with a look at basic memory systems. An interesting series of events must occur before we can say “I remember.” Many people think of memory as “a dusty storehouse of facts.” In reality, memory is an active system that receives, stores, organizes, alters, and recovers information (Baddeley, 1996). In some ways memory acts like a computer (œFig. 9.1).
Incoming information is first encoded, or changed into a usable form. This step is like typing data into a computer. Next, information is stored, or held in the system. (As we will see in a moment, human memory can be pictured as three separate storage systems.) Finally, memories must be retrieved, or taken out of storage, to be useful. If you’re going to remember all of the 9,856 new terms on your next psychology exam, you must successfully encode, store, and retrieve them.
What are the three separate memory systems just mentioned?
Psychologists have identified three stages of memory. To be stored for a long time, information must pass through all three (œFig. 9.2).
Storage Retrieval Encoding
œ Figure 9.1 In some ways, a computer acts like a mechanical memory system.
Both systems process information, and both allow encoding, storage, and retrieval of data.
Memory The mental system for receiving, encoding, storing, organizing, altering, and retrieving information.
Encoding Converting information into a form in which it will be retained in memory.
Storage Holding information in memory for later use.
Retrieval Recovering information from storage in memory.
© CORBIS
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Sensory Memory
Let’s say a friend asks you to pick up several things at a market.
How do you remember them? New information first enters sensory memory, which can hold an exact copy of what is seen or heard, for a few seconds or less. For instance, look at a flower and then close your eyes. An icon (EYE-kon), or fleeting mental image, of the flower will persist for about one-half second.
Similarly, when you hear information, it is held in sensory memory as an echo for up to 2 seconds (Schweickert, 1993). (An
echo is a brief continuation of activity in the auditory system.)
Let’s say your attention wanders as your friend names the last item on her shopping list.Without thinking, you ask “What did you say?” But before she can answer, you realize you already know what the last item is. This ability to mentally “play back” what someone else just said is based on echoic memory (Eysenck & Keane, 1995). In general, sensory memory holds information just long enough to transfer it to the second memory system (Neath, 2002).
Short-Term Memory
Not everything we see or hear stays in memory. Imagine that a radio is playing in the background as your friend reads her shopping list.Will you remember what the announcer says too?
Probably not, because selective attention (focusing on a selected portion of sensory input) controls what information moves on to short-term memory. Short-term memory (STM)
holds small amounts of information for a brief time. By paying attention to your friend, you will place the shopping list in short-term memory (while you ignore the voice on the radio saying, “Buy Burpo Butter”).
How are short-term memories encoded? Short-term memories can be stored as images. But more often they are stored
phonetically (by sound), especially in recalling words and letters (Neath, 2002). If you are introduced to Tim at a party and you forget his name, you are more likely to call him by a name that sounds like Tim (Jim, Kim, or Slim, for instance), rather than a name that sounds different, such as Bob or Mike. Your friend with the shopping list may be lucky if you don’t bring home jam instead of ham and soap instead of soup!
Short-term memory is a temporary storehouse for small amounts of information. When you dial a phone number or briefly remember a shopping list, you are using STM. Notice that information is quickly “dumped” from STM and forever lost. Short-term memory prevents our minds from storing useless names, dates, telephone numbers, and other trivia. At the same time, it provides an area of working memory where we do much of our thinking.Working memory acts as a sort of “mental scratchpad.” It briefly holds information while other mental activities are taking place, such as when you do mental arithmetic (Tuholski, Engle, & Baylis, 2001).
As you may have noticed when dialing a telephone, STM is very sensitive to interruption, or interference. You’ve probably had something like this happen with STM: Someone leaves a phone number on your answering machine. You repeat the number to yourself as you start to dial. Then the doorbell rings and you rush to see who is there. When you return to the phone, you have completely forgotten the number. You listen to the message again and memorize the number. This time as you begin to dial, someone asks you a question. You answer, turn to the phone, and find that you have forgotten the number. Notice again that human working memory can handle only small amounts of information. It is very difficult to do more than one task at a time in STM (Miyake, 2001).
Long-Term Memory
If short-term memory is brief, easily interrupted, and limited in “size,” how do we remember for greater lengths of time? Information that is important or meaningful is transferred to long-term memory (LTM), a more permanent storehouse for information.
LTM contains everything you know about the world— from aardvark to zucchini, math to Myst, facts to fantasy. And yet, there appears to be no danger of running out of room. LTM can hold nearly limitless amounts of information. In fact, the more you know, the easier it becomes to add new information
Incoming information Sensory memory Selective attention Short-term memory Successfully coded for storage in LTM Rehearsal buffer Not attended to Not coded while in STM Forgotten Long-term memory Forgotten
œ Figure 9.2 Remembering is thought to involve at least three steps. Incoming information is first held for a second or two by sensory memory. Information selected by attention is then transferred to temporary storage in short-term memory. If new information is not rapidly encoded or rehearsed, it is forgotten.
If it is transferred to long-term memory, it becomes relatively permanent, although retrieving it may be a problem. The preceding is a useful, but highly simplified, model of memory; it may not be literally true of what happens in the brain (Eysenck & Keane, 1995).
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to memory. This is the reverse of what would happen if LTM could be “filled up” (Eysenck & Keane, 1995). It is also one of many reasons for getting an education.
Are long-term memories also encoded as sounds? They can be.
But typically, long-term memories are stored on the basis of
meaning, not by sound. If you make an error in LTM, it will probably be related to meaning. For example, if you are trying to recall the word barn from a memorized list, you are more likely to mistakenly say shed or farm than yarn or darn. If you can link information in STM to knowledge already stored in LTM, it gains meaning. This makes it easier to remember. As an example, try to memorize this story:
With hocked gems financing him, our hero bravely defied all scornful laughter.
“Your eyes deceive,” he had said, “An egg, not a table, correctly typifies this unexplored planet. ”Now three sturdy sisters sought proof. Forging along, days became weeks as many doubters spread fearful rumors about the edge. At last from nowhere welcome winged creatures appeared, signifying momentous success (Adapted from Dooling & Lachman, 1971).
This odd story emphasizes the impact that meaning has on memory. People given the title of the story were able to remember it far better than those not given a title. See if the title helps you as much as it did them. The title is “Columbus Discovers America.”
Dual Memory
Most of our daily memory chores are handled by STM and LTM. To summarize their connection, picture short-term memory as a small desk at the front of a huge warehouse full of filing cabinets (LTM).As information enters the warehouse, it is first placed on the desk. Because the desk is small, it must be quickly cleared off to make room for new information. Unimportant items are simply tossed away.Meaningful or important information is placed in the files (LTM).
When we want to use knowledge from LTM to answer a question, the information is returned to STM. Or, in our analogy, a folder is taken out of the files (LTM) and moved to the desk (STM), where it can be used. Now that you have a general picture of memory it is time to explore STM and LTM in more detail. But first, here’s a chance to rehearse what you’ve learned.
Short-Term Memory—Do You Know the Magic Number?
To make good use of your memory, it is valuable to know more about the characteristics of STM and LTM. It’s time to dig deeper into the inner workings of our primary memory systems.
How much information can be held in short-term memory?
For an answer, read the following numbers once. Then close the book and write as many as you can in the correct order.
8 5 1 7 4 9 3
Sensory memory The first stage of memory, which holds an exact record of incoming information for a few seconds or less.
Icon A mental image or visual representation.
Echo A brief continuation of sensory activity in the auditory system after a sound is heard.
Selective attention Voluntarily focusing on a selected portion of sensory input.
Short-term memory (STM) The memory system used to hold small amounts of information for relatively brief time periods.
Phonetic storage Storing a word in memory on the basis of its sound.
Working memory Another name for short-term memory, especially when it is used for thinking and problem solving.
Long-term memory (LTM) The memory system used for relatively permanent storage of meaningful information.
RELATE
Wave a pencil back and forth in front of your eyes while focusing on something in the distance.The pencil’s image looks transparent.Why? (Because sensory memory briefly holds an image of the pencil. This image persists after the pencil passes by.)
Think of a time today when you used short-term memory (such as briefly remembering a phone number, an Internet address, or someone’s name).How long did you retain the information? How did you encode it? How much do you remember now?
How is long-term memory helping you read this sentence? If the words weren’t already stored in LTM, could you read at all? How else have you used LTM today?
LEARNING CHECK
Match: A. Sensory memory B. STM C. LTM
1. _____ Working memory
2. _____ Holds information for a few seconds or less
3. _____ Stores an icon or echo
4. _____ Permanent, unlimited capacity
5. _____ Temporarily holds small amounts of information
6. _____ Selective attention determines its contents
7. STM is improved by interruption, or interference, because attention is more focused at such times. T or F?
CRITICAL THINKING
8. Why is sensory memory important to filmmakers?
ANSWERS
K N O W L E D G E B U I L D E R
Memory Systems
1. B 2. A 3. A 4. C 5. B 6. B 7. F 8. Without sensory memory,a movie would look like a flickering series of still pictures.The brief persistence of icons in sensory memory is what blends one movie frame into the next.
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This is called the digit-span test. It is a measure of attention and short-term memory. If you were able to correctly repeat 7 digits, you have an average short-term memory. Now try to memorize the following list, reading it only once.
7 1 8 3 5 4 2 9 1 6 3 4 This series was probably beyond your short-term memory capacity.
Psychologist George Miller found that short-term memory is limited to the “magic number” 7 (plus or minus 2) information bits (Miller, 1956). A bit is a single meaningful “piece” of information, such as a digit. It is as if short-term memory has 7 “slots”or “bins” into which separate items can be placed.Actually, a few people can remember up to 9 bits, and for some types of information 5 bits is the limit. Thus, an average of 7 information bits can be held in short-term memory (Neath, 2002).
When all of the “slots” in STM are filled, there is no room for new information. Picture how this works at a party: Let’s say your hostess begins introducing everyone who is there, “Chun, Dasia,Marco, Roseanna, Cholik, Shawn, Kyrene . . .” “Stop,” you think to yourself. But she continues, “Nelia, Jay, Efren, Frank, Marietta, Jorge, Patty, Amit, Ricky.” The hostess leaves, satisfied that you have met everyone. And you spend the evening talking with Chun, Dasia, and Ricky, the only people whose names you remember!
Recoding
Before we continue, test your short-term memory again, this time with letters. Read the following letters once, then look away and try to write them in the proper order.
TVI BMUS NY MCA Notice that there are 12 letters, or “bits” of information. This should be beyond the 7-item limit of STM. However, since the letters are in four groups, or chunks of information, many students are able to memorize them. Information chunks are made up of bits of information grouped into larger units.
How does chunking help? Chunking recodes (reorganizes) information into units that are already in LTM. For example, you may have noticed that NY is the abbreviation for New York. If so, the two bits N and Y became one chunk. In an experiment that used lists like this one, people remembered best when the letters were read as familiar meaningful chunks: TV, IBM, USN, YMCA (Bower & Springston, 1970). If you recoded the letters this way, you probably remembered the entire list.
Chunking suggests that STM holds about 5 to 7 of whatever units we are using. A single chunk could be made up of numbers, letters, words, phrases, or familiar sentences (Barsalou, 1992). Picture STM as a small desk again. Through chunking, we combine several items into one “stack” of information. This allows us to place 7 stacks on the desk, where before there was only room for 7 separate items. While you are studying, try to find ways to link 2, 3, or more separate facts or ideas into larger chunks, and your memory will improve. Psychologist Nelson Cowan (2001) believes that STM may actually hold only 4 items, unless some chunking has occurred. The clear message is that creating information chunks is the key to making good use of your short-term memory.
Rehearsal
How long do short-term memories last? They disappear very rapidly.
However, you can prolong a memory by silently repeating it, a process called maintenance rehearsal. You have probably briefly remembered an address or telephone number this way.
The more times a short-term memory is rehearsed, the greater its chances of being stored in LTM (Barsalou, 1992). In a sense, rehearsing information allows you to “see” it many times, not just once (Nairne, 2002).
What if rehearsal is prevented, so a memory can’t be recycled?
Without maintenance rehearsal, STM is incredibly short. In one experiment, people heard meaningless syllables like XAR followed by a number like 67. After they heard the number, subjects began counting backward by threes (so they couldn’t repeat the syllable). After only 18 seconds of delay, their memory scores fell to zero (Peterson & Peterson, 1959).
After 18 seconds without rehearsal, the short-term memories were gone forever! Keep this in mind when you get only one chance to hear important information. For example, if you are introduced to someone and the name slips out of STM, it’s gone forever. Of course, you could try saying something like, “I’m curious, how do you spell your name?”Unfortunately, the response is often an icy reply like, “B-O-B S-M-I-T-H, it’s really not too difficult.” To avoid embarrassment, pay careful attention to the name, repeat it to yourself several times, and try to use it in the next sentence or two—before you lose it (Neath, 2002).
Elaborative rehearsal, which makes information more meaningful, is a far better way to form lasting memories. Elaborative rehearsal links new information to memories that are already in LTM.When you are studying, you will remember more if you elaborate, extend, and think about information. As you read, try to frequently ask yourself “why” questions, such as “Why would that be true?” (Willoughby et al., 1997). Also, try to relate new ideas to your own experiences and knowledge (Hartlep & Forsyth, 2000).
Long-Term Memory— Where the Past Lives
An electrode touched the patient’s brain. Immediately she said, “Yes, sir, I think I heard a mother calling her little boy somewhere.
It seemed to be something happening years ago. It was somebody in the neighborhood where I live.” A short time later the electrode was applied to the same spot. Again the patient said, “Yes, I hear the same familiar sounds, it seems to be a woman calling, the same lady” (Penfield, 1958). These statements were made by a woman undergoing brain surgery. There are no pain receptors in the brain, so the patient was awake as her brain was electrically stimulated (œFig. 9.3). When acti-
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vated, some brain areas seemed to produce vivid memories of long-forgotten events.
Permanence
Are all of our experiences permanently recorded in memory? Results like those described led neurosurgeon Wilder Penfield to claim that the brain records the past like a “strip of movie film, complete with sound track” (Penfield, 1957). But as you know, this is an exaggeration. Many events never get past short-term memory. Also, brain stimulation produces memory-like experiences in only about 3 percent of cases. Most reports resemble dreams more than memories, and many are clearly imaginary.
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