Chapter 7 Memory

Editor's Notes

• #4: Memory is much more than taking in information and putting it in some mental compartment…we have to get it back out, too. Many psychologists study factors that help or hinder memory storage and retrieval…thus attempting to answer 3 basic questions… How does information get into memory? How is information maintained in memory? How is information pulled back out of memory?
• #6: The first step in getting information into memory is to pay attention to it. Attention involves focusing awareness on a narrowed range of stimuli or events. Selective attention is a term used by many psychologists to describe this paying-attention-to-something process; however, the word selective is really redundant…attention IS selection of input. Usually, attention is likened to a filter in an information-processing model of memory…the filter screens out most stimuli, while allowing a select few to get by. Much research has been done to determine whether this filtering process occurs early in the information processing sequence or later. It appears that both may be at play…sometimes you are paying attention to someone talking with you at a party, and you suddenly hear your name from across the room.
• #9: According to Craik and Lockhart, whether or not we will be able to remember something depends on how deeply we processed the information. Figure 7.4 illustrates different levels of processing.
• #12: Elaboration is a process by which a stimulus is linked to other information at the time of encoding…for example, you are studying phobias for your psychology test, and you apply this information to your own fear of spiders. Elaboration often consists of thinking of examples…self-generated examples seem to work best. Visual imagery involves the creation of visual images to represent the words to be remembered…concrete words are much easier to create images of (example, juggler vs. truth). Dual-coding theory holds that memory is enhanced by forming semantic or visual codes, since either can lead to recall. Self-referent encoding involves deciding how or whether information is personally relevant, that is, information that is personally meaningful is more memorable.
• #13: Plato and Aristotle compared memory to a block of wax that differed in size and hardness for various individuals…remembering was like stamping an impression into the wax… Today, with technological advances, the analogies have become much more sophisticated... Atkinson and Shiffrin, 1968, proposed an analogy between information storage by computers and information storage in human memory – the information processing approach. Basically, this approach divides memory into 3 different stores: sensory, short-term memory, and long-term memory. This is depicted in the following figures.
• #14: Using the computer as a model, memory researchers seek to trace the flow of information as it is mentall processed. In this information-processing model , a stimulus that registers on our senses can be remembered only if it 1. Draws attention, which brings it into consciousness; 2. Is encoded, or transferred to storage sites in the brain, and 3. Is retrieved for use at a later time. Within this information-processing memory approach, three types of memory have been distinguished: sensory, short-term and long-term. Sensory memory stores all stimuli that register on the senses, holding literal copies for a brief moment ranging from a fraction of a second to three seconds. Sensations that do not draw attention tend to vanish, but those we ‘notice’ are transferred to short-term memory , another temporary storage system that can hold seven or so items of information for about 20 seconds. Although STM fades quickly, information can be held for a longer period of time through repetition and rehearsal. When people talk about attention span, they are referring to short-term memory. Finally, long-term memory is a somewhat permanent storage system that can hold vast quantities of information for many years. Science writer Isaac Asimov once estimated that LTM takes in a quadrillion separate bits of information in the course of a lifetime. Mathematician John Griffith estimated that, from birth to death, the average person stores five hundred times more information than the Encyclopedia Britannica . When people talk about memory, long-term memory is typically what they have in mind. We’ll talk about each of these in a little more detail later on.
• #15: Many events register in sensory memory. Those that are noticed are briefly stored in short-term memory; those that are encoded are transferred to a more permanent facility. As shown forgetting may be caused by failures of attention, encoding, or retrieval. Note, however, that this is only a model and does NOT mean that the brain has three separate storage bins. This is only one view of how memory works. There is a radically different view. Most computers process instructions in fixed sequence, one linear step at a time. In contrast, the human brain performs multiple operations simultaneously, ‘in parallel’. Thus, some cognitive psychologists have rejected the information-processing model in favor of parallel-processing models in which knowledge is represented in a web-like network of connections among thousands of interacting ‘processing units’ all active at once. The two main questions we’ll be asking ourselves throughout this chapter are: How are memories stored? And to what extend are our memories of the past faithful to reality?
• #16: Take a flashlight into a dark room, turn it on, shine it on a wall, and wave it quickly in a circular motion. What do you see? If you twirl it fast enough, the light will appear to leave a glowing trail, and you’ll see a continuous circle. The reason: Even though the light illuminates only one point in the circle at a time, your visual system stores a ‘snapshot’ of watch point as you watch the next point. The visual image is called an icon, and the snapshot it stores is called iconic memory . People typically don’t realize that a fleeting mental trace lingers after a stimulus is removed from view. Nor did cognitive psychologists realize it until George Sperling’s ingenious series of experiments that we will get to in a few slides.
• #17: Sensory Memory is basically information preserved in its original sensory form for a brief time. This type of memory allows the sensation to linger briefly after the sensory stimulation is over…in the visual system, an afterimage. The visual and auditory sensory stores appear to decay after about ¼ second George Sperling (1960) performed a classic experiment on the visual sensory store, illustrating how brief the sensory store actually is…his experiment is depicted in the following figure .
• #18: Sperling instructed subjects to stare at the center of a blank screen. Then he flashed an array of the letters for 1/20 of a second and asked subjects to name as many of the letters as possible. Try it for yourself . You’ll probably recall about a a handful of letters. In fact, Sperling found that no matter how large the array was, subjects could name only four or five items. Why? One possibility is that people can register just so much visual input in a single glance – that twelve letters is too much to see in so little time. A second possibility is that all letters registered by the image faded before subjects could report them all. Indeed, many subjects insisted that they were able to ‘see’ the whole array but then forgot some of the letters before they could name them. Did the information that was lost leave a momentary trace, as subjects had claimed, or did it never register in the first place? To test these alternative hypotheses, Sperling devised the ‘partial-report technique’. Instead of asking subjects to list all the letters, he asked them to name only one row in each array – a row that was not determined until after the array was shown. In this procedure, each presentation was immediately followed by a tone signaling which letters to name: A high-pitched tone indicated the top line; a medium pitch, the middle line; a low pitch, the bottom line.
• #23: If the saw the entire array, subjects should have been able to report all the letters in a prompted row correctly – regardless of which row was prompted. Sperling was right: subjects correctly recalled 3 letters per row. In other words, all 9 letters, not 4 or 5, were instantly registered in consciousness before fading, held briefly in iconic memory. To determine how long this type of memory lasts, Sperling next varied the time between the letters and the tone that signaled the row to be recalled. He found that the visual image started to fade as the interval was increased to 1/3 of a second and had almost completely vanished 2/3 of a second later. Since this study, researchers have found when it comes to pictures of objects or scenes, words, sentences, and other visual stimuli briefly presented, people form ‘fleeting memories’ that last for just a fraction of a second. Not an afterimage because Sperling showed he could present the letters to one eye and influence the memory by presenting a bright flash to the other eye. This would not have worked if the visual information was stored on the retina.
• #28: A similar phenomenon exists for auditory stimuli. The next time you listen to the radio, notice after you turn it off how an ‘echo’ of the sound seems to reverberate inside your head. This auditory sensory register is called echoic memory . Just how much auditory input is stored in echoic memory? In a study modeled after Sperling’s, Christopher Darwin and others (1972) put headphones on subjects and all at once played three sets of spoken letters – in the right ear, in the left ear, and in both ears at once. Subjects then received a visual signal indicating which set to report. Using this study and others, researchers have found that echoic memory holds only a few items but lasts for two or three seconds, and perhaps even longer, before activation in the auditory cortex fades. Whether a sensory memory system stores information for one-third of a second or for three seconds, you might wonder: What’s the point of having a ‘memory’ that is so quick to decay? To answer this question, try to imagine what your perceptions of the world would be like without sensory memories. Without the visual icon, for instance, you would lose track of what you see with every blink of the eye – as if you were viewing the world through a series of snapshots rather than on a continuous film. Similarly, it would be hard to understand spoken language without the persistent traces of echoic memory. Speech would be heard as a series of staccato sounds rather than as connected words and phrases. In fact, we have other sensory memories as well – for touch, smell, and taste stimuli.
• #29: Short-term memory is defined as a limited-capacity store that can maintain unrehearsed information for up to about 20 seconds. George Miller (1956) wrote a famous paper called “The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information," where he illustrated that the average person can hold between 5 and 9 chunks of information in STM. A chunk of information is a group of familiar stimuli stored as a single unit…for example, the following numbers 8 -6- 7- 5- 3- 0- 9 can be thought of as 7 individual numbers or they can be chunked together in groups of 2, 3, etc. STM also has a limited duration…in other words, information can only be kept there for a brief time before it is lost, unless rehearsal occurs. Rehearsal is the process of repetitively verbalizing or thinking about the information…keeping it in use. Peterson and Peterson (1959) conducted a study illustrating how quickly information is lost from STM…this study is illustrated on the next slide.
• #33: It’s important to note that to the extent that one stimulus captures our attention, others may be ignored – sometimes with startling effects on memory. For example, research on eyewitness testimony shows that when a criminal displays a weapon, witnesses are less able to identify the culprit than if no weapon is present. Why? One reason is that the witness’s eyes fixate on the weapon, particularly when it comes as a surprise, thereby drawing attention away from the face. To demonstrate, researchers showed subjects slides of a customer who walked up to a bank teller and pulled out either a gun or a checkbook. By recording eye movements, these researchers found that subjects spent more time looking at the gun than at the checkbook. The result: impairment in their ability to identify the criminal in a lineup. Limited by attentional resources, short-term memory can hold a small number of items. How small an number? The average person can store seven or so items – regardless of whether they are numbers, letters, words, or names. Okay, so short-term memory can accommodate only seven items, and that number may be smaller, but here’s the hitch: Although an item may consist of one letter or digit, these items can be grouped into chunks of words, sentences, and large numbers – thus enabling us to use our storage capacity more efficiently. The activity we did at the start of this section demonstrates the effects of chunking – you were better able to remember more numbers when they were chunked into significant years than when they appeared to be random numbers. Chunking enables us to improve our short-term memory span by using our capacity more efficiently. You may be limited to seven or so chunks, but you can learn to increase the size of those chunks. Without rehearsal, some researchers find that people can only remember about 4 plus or minus 2 chunks. With rehearsal, we’re back to the magic seven plus or minus two. But with serious training, people can increase the size of the chunks so that you are remembering large quantities of material. To demonstrate, a group of researchers trained two male university students, both long-distance runners and of average intelligence, for several months. For an hour a day, three or four days a week, these students were asked to recall random strings of numbers. If they recalled a sequence correctly, another digit was added to the next sequence and the task was repeated. If they made a mistake, the number of digits in the next sequence was reduced by one. Before practicing, their memory span was four to seven digits. After six months, they were up to eighty items. In one session, for example, the experimenter read the following numbers in order: After two minutes of concentration, the subject repeated all seventy-three digits, in groups of three and four. How did he do it? Given no special instructions, the subject developed his own elaborate strategy: he converted the random numbers into ages, dates, and racing times. Thus, 893 became 89.3 (a very old person); 1944 became 1944 (near the end of the second world war); and 3492 became 3 minutes and 49.2 seconds (nearly a world’s record for the mile).
• #35: 30 years of research eventually uncovered a number of problems with the original model of STM…STM is not limited to phonemic encoding, as originally thought, and decay is not the only process responsible for loss of information. These and other findings indicated that STM might be a much more complicated aspect of memory. Alan Baddeley (1986-1992) proposed a more complex model of STM that characterizes it as “working memory," with 4 components. The phonological rehearsal loop represented ALL of STM in the original model. This component is active when one uses recitation to temporarily hold on to information. The visuospatial sketchpad allows temporary holding and manipulation of visual images (mentally rearrange the furniture in your bedroom). The executive control system handles the limited amount of information juggled at one time as people engage in reasoning and decision making…at work when you weigh pros and cons of something. The episodic buffer is a temporary, limited capacity store that allows the various components of working memory to integrate information, and that serves as an interface between working and LTM.
• #38: While most researchers agree that LTM has an unlimited capacity; that is, our memory store never gets FULL, much debate remains over whether storage is permanent. Flashbulb memory and hypnosis based memory suggest that LTM is indeed permanent, that the only reason we forget is that we aren’t able to access information that is still in LTM (interference theory). Research shows, however, that flashbulb and hypnosis based memories are not always accurate. Is the information still there, or does it decay over time, and we make up for this by building up decayed memories so that they make sense? And are STM and LTM really different stores? We used to think that phonemic encoding occurred in STM and semantic (or meaning based) encoding in LTM. Now we know that both occur for both. We also used to think that decay occurred in STM and interference in LTM, with regard to forgetting. Now, it is unclear what exactly occurs in LTM, it may be both. Some researchers argue that STM and LTM are the same thing, that STM is just a little part of LTM that is in a state of heightened activation, although the multiple stores view is still dominant.
• #39: Do you remember your fourth birthday, the name of your first-grade teacher, or the smell of floor wax in the corridors of your elementary school? Can you describe a dream that you had last night or recite the words of the national anthem? To answer these questions, you would have to retrieve information from the mental warehouse of long-term memory. Like the hard drive on a computer, long-term memory is a relatively enduring storage system that has the capacity to retain vast amounts of information for long periods of time. We’ll examine long-term memories of the recent and remote past – how they are encoded, stored, retrieved, forgotten, and even reconstructed in the course of a lifetime. Information can be kept alive in short-term working memory by rote repetition or maintenance rehearsal. But to transfer something into long-term memory, you would find it much more effective to use elaborative rehearsal – a strategy that involves thinking about the material in a more meaningful way and associating it with other knowledge that is already in long-term memory. The more deeply you process something, the more likely you are to recall it at a later time. To demonstrate this process, Craik & Tulving (1975) showed a subject a list of words, one at a time, and for each asked them for 1) a simple visual judgment that required no thought about the words themselves (Is the word printed in capital letters?); 2) an acoustic judgment that required subjects to at least pronounce the letters as words (Does the word rhyme with smell?); or 3) a more complex semantic judgment that compelled subjects to think about the meaning of the words (Does the word fit the sentence ‘I saw a blank in the pond’?). Subjects did not realize that their memory would be tested later. Yet words that were processed at a ‘deep’ level, in terms of meaning, were more easily recognized than those processed at a ‘shallow’ level. Does making complex semantic judgments, compared to simple visual judgments, activate different regions of the brain? Is it possible to see physical traces of deep processing? Using functional MRI technology, researchers devised a study similar to the Craik & Tulving study where subjects were shown stimulus words on a computer and were instructed to determine whether the words were concrete or abstract (a semantic judgment) or simply whether they were printed in uppercase or lowercase letters (a visual judgment). As in past research, subjects later recalled more words for which they made semantic rather than visual judgments. In addition, however, the brain-imaging measures showed that processing the words in semantic terms triggered more activity in a part of the frontal cortex of the language-dominant left hemisphere. Perhaps the most effective form of elaborative rehearsal is the linking of new information to the self. In one study, subjects sat in front of a microcomputer and looked at forty trait words (for example, shy, friendly, ambitious ). In some cases, they were told to judge whether the words were self-descriptive; in others,they judged the word’s length, sound, or meaning. When asked to list as many of the words as they could, subjects remembered more after thinking about the words in reference to themselves than for other purposes. Apparently, the self can be used as a memory aid: By viewing new information as relevant to ourselves, we consider that information more fully and organize it around common themes. The result is an improvement in recall. Hence, why I tell you guys to try and personalize this material as much as possible, even if it is just coming up with examples of when these things have happened to you…it increases your likelihood of remembering it for the exam. Although the transfer of information to long-term memory often requires a great deal of thought and effort, certain types of information are encoded automatically and without conscious control. When you meet someone for the first time, you may have trouble remembering their name but you can easily recall their face. Similarly, people encode information about time, spatial locations, and event frequencies without conscious effort.
• #40: It seems that we have more than one type of long-term memory. Researchers now commonly distinguish two types of memory. One is procedural memory , a ‘know how’ memory that consists of our stored knowledge of well-learned habits and skills – such as how to drive, swim, type, ride a bike, and the tie shoelaces. The second type is declarative memory , which consists of both semantic memories for facts about the world – such as who Michael Jordan is, what a dollar is worth, what you need to access the World Wide Web, and what the word ‘gravity’ means – and episodic memories that we have about ourselves – such as who our parents are, where we went to school, and what our favorite movie is. The distinction is important because people with amnesia are often unable to recall declarative memories of facts and events, yet they still retain many of the skills they had learned and committed to procedural memory. With all that’s stored in long-term memory – habits, skills, verbal information and knowledge of the words, names, dates, faces, pictures, personal experiences, and the like – it’s amazing that anything can ever be retrieved from this vast warehouse. Surely our knowledge must be organized in memory, perhaps the way books are filed in a library. One popular view is that memories are stored in a complex web of associations, or semantic networks . According to proponents of this view, items in memory are linked together by semantic relationships. When one item is brought to mind, the pathways leading to meaningfully related items are primed – thus increasing the likelihood that they too will be retrieved. A good deal of research supports the notion that memories are stored in semantic networks. When subjects are given a list of sixty words that fall into four categories (animals, professions, names, and fruits) – even if the words are presented in a mixed order – subjects later tend to recall them in clusters. In other words, retreiving tiger is more likely to trigger one’s memory for baboon than for dentist, Jason, or banana.
• #41: Clustering is the tendency to remember similar or related items in groups. Conceptual hierarchies are multilevel classification systems based on common properties among items. Schemas are organized clusters of knowledge about a particular object or event abstracted from previous experience. A script is a particular type of schema, organizing what a person knows about common activities…for example going to a restaurant. Research shows that people are more likely to remember things that are consistent with their schemas than things that are not…the reverse is also true – people sometimes exhibit better recall if information really clashes with a schema. Semantic networks consist of nodes representing concepts, joined together by pathways that link related concepts….explains why thinking of butter makes bread easier to remember…depicted on following slide. Connectionist, or parallel distributed processing models, assume that cognitive processes depend on patterns of activation in highly interconnected computational networks that resemble neural networks….that is, this model of memory uses as inspiration the way neurons appear to handle information through connections…according to this model, specific memories correspond to specific patterns of activation in these networks.
• #44: The tip-of-the-tongue phenomenon shows that recall is often guided by partial information about a word….retrieval cues. Memories can also be reinstated by context cues…easier to recall long-forgotten events if you return after a number of years to a place where you used to live. Memories are reconstructions of the past, which may not be entirely accurate. Research shows that reconstructions can be influenced by new information…the misinformation effect. Elizabeth Loftus has shown that eyewitness testimony can be influenced by information presented to witnesses. Example…showed a video of two cars in an accident…asked some people how fast the cars were going when they HIT each other, asked others how fast the cars were going when the SMASHED INTO each other…a week later asked whether there was any broken glass in the video…the “smashed into” group said yes, the “hit” group said no. The misinformation effect is explained in part by the unreliability of source monitoring…the process of making attributions about the origins of memories…people make decisions at the time of retrieval about where their memory is coming from (did I read that somewhere or think of it on my own?…cryptomnesia is inadvertent plagiarism that occurs when you think you came up with it but were really exposed to it earlier). Reality monitoring is a type of source monitoring involving determining whether memories are based in actual events (external sources) or your imagination (internal sources)…kidnapped by aliens? Possible error in reality monitoring.
• #45: Once information is stored, how do you know it exists? Because people can openly report their recollections, this seems like a silly question. In fact, however, this is one of the thorniest questions confronting cognitive psychologists. Hermann Ebbinghaus was not only the first person to study memory systematically but also the first to realize that a memory may exist without awareness. In his words “These experiences remain concealed from consciousness and yet produce an effect which is significant and which authenticates their previous experience.” Memory without awareness illustrates how human beings can be both competent and incompetent at the same time, and it poses a profound challenge to the researcher: If people have memories they cannot report, how can we ever know these memories exist? To his credit, Ebbinghaus devised a simple but clever technique. He tested memory by its effect on performance. Acting as his own subject, he would learn a set of nonsense syllables and then count the number of trials it later took him to relearn the same list. If it took fewer trials the second time around than the first, then he must have retained some of the material – even if he could not consciously recite it. In recent years, other techniques have been devised. Basically, there are two types of tests, and each assesses a different type of memory; one explicit, the other implicit. Explicit memory is a term used to describe the recollections of facts and events that people try to retrieve in response to direct questions. In contrast, implicit memory is a term used to describe the retention of information without awareness, as measured by its indirect effects. Why is this distinction important? The reason, as we’ll see, is that people often exhibit dissociations between the two types of tasks. That is, people will consciously forget (have no explicit memory) of that experience. There are different ways to interpret this pattern. Some psychologists believe that explicit and implicit memory are separate systems that are controlled by different parts of the brain, whereas others believe that the dissociations merely indicate differences in the way information is encoded and retrieved. Either way, it’s useful to consider these two aspects of memory separately.
• #46: Okay, can you all name all of Walt Disney’s Seven Dwarfs? Try it. When I was put to the test, I could only name about four…I always forget about Bashful, Sneezy, and Happy! This type of task, in which a person is asked to reproduce information without the benefit of external cues, is an example of a free-recall test of explicit memory. Other examples include taking an essay exam, describing a criminal’s face to the police, and struggling to recall a childhood experience. Now if I had given you a list of ten possible dwarf names and asked you to indicate which of them are accurate, that would have been a recognition task . This task requires you to select a remembered item from a list of alternatives. So are taking a multiple-choice exam and picking a criminal from a lineup, or identifying photographs from a family album. Research shows that recall and recognition are both forms of explicit memory in that people are consciously trying to retrieve the information. There is, however, a key difference: People tend to perform better at recognition. The seven dwarfs task illustrates the point. When college students were asked to recall the characters on their own, they correctly produced an average of 69% of the names. Yet, when they made selections from a list, the accuracy rate increased to 86% . The fact that recognition is easier than recall tells us that forgetting sometimes occurs not because memory has decayed or because we didn’t encode the information but because the information is difficult to reclaim from storage. Retrieval failure is a common experience. Have you ever felt as thought a word or name you were trying to recall was just out of reach – on the tip of your tongue? In a classic study of the tip-of-the-tongue phenomenon, Brown & McNeill prompted this experience by giving students definitions of uncommon words and asking them to produce the words themselves. For example, what is ‘the green-colored matter found in plants’? And what is ‘the art of speaking in such a way that the voice seems to come from another place’? Most often, subjects either knew the word right away or were certain that they did not know it. But at times, subjects knew they word but could not recall it – a frustrating state that they likened to being on the brink of a sneeze. The experience is an interesting one. When a word is on the tip of the tongue, subjects often come up with other words that are similar in sound or meaning. Groping for chlorophyll , subjects might say chlorine or cholesterol . For ventroliquism , they produce words such as ventilate or vernacular . In fact, a surprising number of people will guess the correct first letter, last letter, and number of syllables contained in the missing word. Recognition is often easier than recall because recognition tasks contain retrieval cues, or reminders. A retrieval cue is a stimulus that helps us to access information in long-term memory. Any stimulus that is encoded along with an experience can later trigger one’s memory of that experience. The retrieval cue may be a picture, a location, a word, a song, another person, or even a fragrance or the mood we’re in.
• #47: To study forgetting empirically, psychologists must measure it precisely. To measure forgetting, we must measure memory. Retention refers to the proportion of material remembered or retained. Three types of tasks are used to measure retention…recall, which involves requiring subjects to reproduce information on their own without any cues…recognition, which involves requiring subjects to select previously learned material from an array of options…and relearning, which involves requiring subjects to relearn previously learned information to see how much LESS time or effort it takes them. Hermann Ebbinghaus studied forgetting using retention in the late 1800s, by using himself as a subject. He found that retention and forgetting occur over time and plotted his data…the famous forgetting curve depicted on the next slide. Current research suggests that this curve is unusually steep, probably due to the fact that Ebbinghaus was using nonsense syllables that are difficult to encode semantically.
• #51: Research indicates that forgetting may be related to encoding, storage, or retrieval processes. Much forgetting may only look like forgetting…it may have never been inserted into memory in the first place…pseudoforgetting…usually due to lack of attention so that encoding does not occur. Ineffective encoding occurs when you encode on a more superficial level than you need to…for example, you are distracted when studying and encode what you are reading on a phonemic rather than a semantic level. Decay theory proposes that forgetting occurs because memory traces fade with time. The negative impact of competing information on retention is called interference. Interference theory holds that people forget information because of competition from other material. Proactive interference occurs when previously learned information interferes with the retention of new information, while retroactive interference occurs when new information impairs the retention for previously learned information. Figure 7.21, presented on the next slide, illustrates the two types of interference.
• #52: Now before we celebrate the virtues of memory and outline the techniques we can use to improve it, let’s stop and ponder the wisdom of William James (you’ll remember him as one of our founding fathers of psychology) who said ‘If we remembered everything, we should on most occasions be as ill off as if we remembered nothing.” James was right. Sometimes it is better to forget – which is why some psychologists have suggested the paradoxical conclusion that forgetting is an adaptive, economical aspect of human memory. Memory failure is a common experience in everyday life. Why? Do memory traces fade with time? Are they displaced by newer memories? Or do memories get buried, perhaps blocked by unconscious forces? As we’ll see, forgetting can result from one of four processes: a lack of encoding, decay, interference, or repression. In the first two, the forgotten information is simply not in long-term memory storage. In the second two, the memory may exist, but it is difficult, if not impossible, to retrieve. Do you know what an American penny looks like? Would you recognize one if you say it? If you were born in the US, you have looked at, held, and counted thousands of pennies in your life. Yet many people cannot accurately draw one from memory, name its features, or distinguish it from a fake. Look at these coins. Which of these is the true penny? When researchers present this task to college students, they find that about 58% did not identify the right coin. The reason for this result is not that the subjects forgot what a penny looks like – it’s that the features were never encoded into long-term memory. And why should they be? So long as you can tell the difference between pennies and other coins, there is no need to attend to the fine details. The penny is not the only common, everyday object whose features we fail to notice. People also have difficulty recalling the features of a dollar bill, computer keyboard, the front-page spread of their favorite newspaper, and even the layout of a telephone – objects we look at and use all the time. The oldest theory of forgetting is that memory traces erode with the passage of time. But there are two problems with this simple explanation. One is that there is no physiological evidence of decay that corresponds to the fading of memory. The second is that time alone is not the most critical factor. Memory for newly learned nonsense syllables fades in a matter of hours, but the foreign language learned in high school is retained for many years. The key blow to the decay theory of forgetting was landed in 1924 by John Jenkins and Karl Dallenbach. Day after day, these researchers presented nonsense syllables to two subjects and then tested their memory after one, two, four, or eight hours. On some days, the subjects went to sleep between learning and testing; on other days, they stayed awake and kept busy. The subjects recalled more items after they had slept than when they were awake and involved in other activities. Jenkins & Dallenbach concluded that ‘forgetting is not so much a matter of decay of old impressions and associations as it is a matter of interference, inhibition, or obliteration of the old by the new.’ To minimize forgetting, you may find it helpful to go to sleep shortly after studying, thus avoiding ‘new information’ interference.
• #53: By showing that memory loss may be caused by mental activity that takes place when we are awake, Jenkins & Dallenbach’s study suggested a third explanation of forgetting – that something learned may be forgotten due to interference from other information. There are two kinds of interference. In proactive interference , prior information inhibits our ability to recall something new. If you try to learn a set of names, formulas, phone numbers, or glossary terms, you will find it more difficult if you had earlier studied a similar set of items. Many years ago, researchers found that the more nonsense-syllable experiments subjects had taken part in, the more forgetting they exhibited in a brand-new study. A related problem is retroactive interference , whereby new material disrupts memory for previously learned information. Thus, subjects in various experiments are at least temporarily less likely to recognize previously seen pictures of nature scenes, faces, and common objects if they are then exposed to similar photographs before being tested. One learning experience can displace – or at least inhibit – the retrieval of another. That is why, when people go back and review a subset of to-be-remembered information, their memory for nonreviewed material suffers.
• #55: The encoding specificity principle holds that the effectiveness of a retrieval cue depends on how well it corresponds to the memory code that represents the stored item…the closer a retrieval cue is to the way we encode the info, the better we are able to remember. The transfer-appropriate processing theory holds that when the initial processing of information is similar to the type of processing required by the subsequent measure of retention, retrieval is easier. Repression involves the motivated forgetting of painful or unpleasant memories. Recent years have seen a surge of reports of repressed memories of child sexual abuse. The authenticity of these repressed memories is challenged by empirical studies that show that it is not at all hard to create false memories and that many recovered memories are actually the product of suggestion. Roediger and McDermott (2000) have shown that when participants are asked to learn a list of words, and another target word that is not on the list but is strongly associated with the learned words is presented, the subjects remember the non-presented target word over 50% of the time…on a recognition test, they remember it about 80% of the time…a memory illusion. While research clearly shows that memories can be created by suggestion, in cases of child sexual abuse memories, for example, this issue becomes quite emotionally charged. Some cases of recovered memories are authentic, and we don’t yet have adequate data to estimate what proportion of recovered memories of abuse are authentic and what proportion are not. Still, this controversy has helped inspire a great deal of research that has increased our understanding of the fallibility and malleability of human memory.
• #56: More than a hundred years ago, Freud observed that his patients often could not recall unpleasant past events from their own lives. In fact, he observed, they would sometimes stop, pull back, and lose their train of thought just as they seemed on the brink of an insight. Freud called this repression , and he said it was an unconscious defense mechanism that keeps painful personal memories under lock and key – and out of awareness. We’ll see later that people who suffer childhood traumas such as war, abuse, and rape sometimes develop ‘dissociative disorders’ characterized by apparent gaps in their explicit memory. Although repression has never been demonstrated in a laboratory setting, psychotherapy case studies suggest that memories can be repressed for long periods of time and recovered in therapy. As we’ll see later, however, it is difficult in actual cases to distinguish between dormant memories of actual past events and falsely constructed memories of experiences that never occurred.
• #58: From a biochemical perspective, memory appears to be related to alterations in synaptic transmission at specific sites. Durable changes in synaptic transmission may be the building blocks of memories. Other research shows that learning causes hormonal changes which may modulate activity in a variety of neurotransmitter systems. Protein synthesis has also been shown to be necessary for memory formation…if you give drugs that interfere with protein synthesis, memory is impaired (at least in chicks and rats). From a neural perspective, memories appear to depend on localized neural circuits in the brain. These are reusable pathways in the brain that may be specific for specific memories. Research indicates that long-term potentiation occurs with learning. Long-term potentiation is a long-lasting increase in neural excitability at synapses along a specific neural pathway. This supports the idea that memory traces consist of specific neural circuits. The anatomy of memory is complex, and many brain structures have been shown to be important in memory. Figure 7.25, on the next slide, illustrates the brain structures involved in memory, while the following slide, Figure 7.26, illustrates the two types of amnesia, retrograde (for prior events) and anterograde (for subsequent events).
• #61: Implicit memory involves incidental, unintentional remembering, whereas explicit memory involves intentional recall. Many theorists argue that implicit and explicit memory rely on different encoding and retrieval processes, while others argue that they are each handled by independent memory systems (procedural – which is memory for actions, skills, operations and conditioned responses, and declarative – which is memory for factual information). It is suspected that the declarative memory system handles explicit memory and procedural implicit memory. Declarative memory can be subdivided into memory for personal facts (episodic) and memory for general facts (semantic). Retrospective memory is memory for past events, whereas prospective memory is remembering to do things in the future.
• #65: Over the years, psychologists have stumbled in a few rare individuals who seem equipped with extraordinary ‘hardware’ for memory. But often, the actors, waiters, and others who impress us with their extraordinary memories are ordinary people who use memory tricks called mnemonics . Can you too boost your recall capacity and improve your study skills by using mnemonics? Let’s consider the self-help implications of this chapter, many of which are described in paperbacks on how to improve your memory. To learn names, dates, vocabulary words, or the contexts in a textbook, you’ll find that practice makes perfect. In general, the more time spent studying, the better. Skimming or speed-reading will not promote long-term retention. In fact, it pays to overlearn – that is, to review the material even after you think you have it mastered. It also helps to distribute your studying over time rather than cram all at once. You will retain more information from four two-hour sessions that from one eight-hour marathon. The sheer amount of practice is important, but only if it’s ‘quality time’. Mindless drills may help maintain information in short-term memory, but long-term retention requires that you think actively and deeply about material – about what it means and how it is linked to what you already know. Sometimes the easiest way to remember a list of items is to use verbal mnemonics, or ‘memory tricks’. Chances are you have already used popular methods such as rhymes (I before E, except after C) and acronyms that reduce the amount of information to be stored (ROY G BIV).
• #66: Most books on improving memory recommend that verbal information be represented as visual images. One popular use of imagery is the method of loci , in which items to be recalled are mentally placed in familiar locations. It works like this: First you memorize a series of objects along a familiar route. For example, you might imagine your morning walk from the bedroom, to the bathroom, visualize the objects you pass: your bed, then the bathroom door, shower, stairs, and so on. These places become pigeonholes for items to be recalled. To memorize a shopping list, for example, you could picture a dozen eggs lined up on the bed, a bag of red apples handing on the bathroom door, and butter in the soap dish of the shower. When you take a mental stroll through the house, the items on the list should pop to mind. The trick is to link new items to others already in memory. Because one learning experience can disrupt memory for another, you should guard against the effects of interference . This problem is common among students, as material learned in one course can make it harder to retain that learned in another. To minimize interference, follow two simple suggestions: First, study right before sleeping and review all the material right before the exam. Second, allocate an uninterrupted chunk of time to one course; then do the same for the others. If you study psychology, then move to biology, then go on to math and back to psychology, each course will disrupt your memory of the others – especially if the material is similar. Context reinstatement: Information is easier to recall when people are in the physical setting in which it was acquired – and in the same frame of mind. The setting and the mood it evokes serve as cues that trigger the retrieval of to-be-remembered information. That’s why actors like to rehearse on the stage where they will later perform. So next time you have an important exam to take, try to study in the room where you’ll take the test.