ENDURING ISSUES IN MEMORY
In this chapter, we will explore the biological bases of memory (Mind-Body), the ways that memory differs among people and across cultures (Diversity-Universality), and the ways that memory changes in the first few years of life (Stability-Change). Finally, we will consider the extent to which memories can be changed by events outside the person, as well as the importance of environmental cues in triggering memories (Person-Situation).
THE SENSORY REGISTERS
Look slowly around the room. Each glance takes an enormous amount of visual information, including colors, shapes, textures, relative brightness, and shadows. At the same time, you pick up sounds, smells, and other kinds of sensory data. All of this raw information flows from your senses into the sensory registers, which are like waiting rooms in which information enters and stays for only a short time. Whether we remember any of the information depends on which operations we perform on it. Although there are registers for each of our senses, the visual and auditory registers have been studied most extensively.
Visual and Auditory Registers
Although the sensory registers have virtually unlimited capacity, information disappears from them quite rapidly (Cowan et al., 2005). A simple experiment can demonstrate how much visual information we take in - and how quickly it is lost. Bring a digital camera into a darkened room, and then take a photograph with a flash. During the split second that the room is lit up by the flash, your visual register will absorb a surprising amount of information about the room and its contents. Try to hold on to that visual image, or icon, as long as you can. You will find that in a few seconds, it is gone. Then compare your remembered image of the room with what you actually saw, as captured in the photograph. You will discover that your visual register took in far more information than you were able to retain for even a few seconds.
Classic experiments by George Sperling (1960) clearly demonstrate how quickly information disappears from the visual register. Sperling flashed groups of letters, organized into three rows, on a screen for just a fraction of a second. When the letters were gone, he sounded a tone to tell his participants which row of letters to recall: A high-pitched tone indicated that they should try to remember the top row of letters, a low-pitched tone meant that they should recall the bottom row, and a medium-pitched tone signaled them to recall the middle row. Using this partial-report technique, Sperling found that if he sounded the tone immediately after the letters were flashed, people could usually recall 3 or 4 of the letters in any of the three rows; that is, they seemed to have at least 9 of the original 12 letters in their visual registers. But if he waited for even 1 second before sounding the tone, his participants were able to recall only 1 or 2 letters from any single row - in just 1 second, then, all but 4 or 5 of the original set of 12 letters had vanished from their visual registers. In everyday life, new visual information keeps coming into the register; and the new information replaces the old information almost immediately (in about a quarter of a second), a process often called masking.
Auditory information fades more slowly than visual information. The auditory equivalent of the icon, the echo, tends to last for several seconds, which, given the nature of speech, is certainly lucky for us. Otherwise, "You did it!" would be indistinguishable from "You did it!" because we would be unable to remember the emphasis on the first words by the time the last words were registered.
Attention
If information disappears from the sensory registers so rapidly, how do we remember anything for more than a second or two? One way is that we select some of the incoming information for further processing by means of attention. Attention is the process of selectively looking, listening, smelling, tasting, and feeling. At the same time, we give meaning to the information that is coming in.
How do we select what we are going to pay attention to at any given moment and how do we give that information meaning? Donald Broadbent (1958) suggested that a filtering process at the entrance to the nervous system allows only those stimuli that meet certain requirements to pass through. Those stimuli that do get through the filter are compared with what we already know, so that we can recognize them and figure out what they mean. If you and a friend are sitting in a restaurant talking, you filter out all other conversation taking place around you, a process known as the cocktail-party phenomenon (Cherry, 1966; Haykin & Chen, 2006). Although you later might be able to describe certain characteristics of those other conversations, such as whether the people speaking were men or women, according to Broadbent, you normally cannot recall what was being discussed, even at neighboring tables. Since you filtered out those other conversations, the processing of that information did not proceed far enough for you to understand what you heard.
Broadbent's filtering theory helps explain some aspects of attention, but sometimes unattended stimuli do capture our attention. To return to the restaurant example, if someone nearby were to mention your name, your attention probably would shift to that conversation. Anne Treisman (1964, 2012) modified the filter theory to account for phenomena like this. She contended that the filter is not a simple on-and-off switch, but rather a variable control - like the volume control on a radio, which can "turn down" unwanted signals without rejecting them entirely. According to this view, although we may be paying attention to only some incoming information, we monitor the other signals at a low volume. Thus, we can shift our attention if we pick up something particularly meaningful. This automatic processing can work even when we are asleep: Parents often wake up immediately when they hear their baby crying, but sleep through other, louder noises.
At times, however, our automatic processing monitor fails, and we can overlook even meaningful information. In research studies, for example, some people watching a video of a ball-passing game failed to notice a person dressed as a gorilla who was plainly visible for nearly 10 seconds (Drew, Vo, & Wolfe, 2013; Mack, 2003). In other words, just because we are looking or listening to something, doesn't mean we are attending to it. Psychologists refer to our failure to attend to something we are looking at as inattentional blindness. Research has shown, for example, that attending to auditory information can reduce one's ability to accurately process visual information, which makes driving while talking on a cell phone a distinctly bad idea (Pizzighello & Bressan, 2008)!
SHORT-TERM MEMORY
Short-term memory (STM) holds the information that we are thinking about or are aware of at any given moment. When you listen to a conversation, when you watch a television show, when you become aware of a headache - in all these cases, you are using STM to both hold onto and to think about new information coming in from the sensory registers. Short-term memory has two primary tasks: to store new information briefly and to work on that (and other) information. Short-term memory is sometimes called working memory, to emphasize the active or working component of this memory system (Aben, Stapert, & Blokland, 2012; Nairne, 2003). The working memory aspect of STM plays a key role in directing our attention to specific stimuli, briefly storing and combining the selected stimuli with other information, and actively rehearsing this information to help us solve problems and find solutions.
Capacity of STM
Chess masters at tournaments demand complete silence while they ponder their next move. You shut yourself in a quiet room to study for final exams. As these examples illustrate, STM can handle only so much information at any given moment. Research suggests that STM can hold about as much information as can be repeated or rehearsed in 1.5 to 2 seconds (Baddeley, 1986, 2002).
To get a better idea of the limits of STM, read the first row of letters in the list that follows just once. Then close your eyes, and try to remember the letters in the correct sequence. Repeat the procedure for each subsequent row.
1. C X W
2. M N K T Y
3. R P J H B Z S
4. G B M P V Q F J D
5. E G Q W J P B R H K
Like most other people, you probably found rows 1 and 2 fairly easy, row 3 a bit harder, row 4 extremely difficult, and row 5 impossible to remember after just one reading.
Now try reading through the following set of 12 letters just once, and see whether you can repeat them: TJYFAVMCFKIB
How many letters were you able to recall? In all likelihood, not all 12. But what if you had been asked to remember the following 12 letters instead? TV FBI JFK YMCA
Could you remember them? Almost certainly the answer is yes. These are the same 12 letters as before, but here they are grouped into four separate "words." This way of grouping and organizing information so that it fits into meaningful units is called chunking (Cowan & Chen, 2009).
By chunking words into sentences or sentence fragments, we can process and even greater amount of information in STM. For example, suppose that you want to remember the following list of words: tree, song, hat, sparrow, box, lilac, cat. One strategy would be to cluster as many of them as possible into phrases or sentences: "The sparrow in the tree sings a song"; "a lilac hat in the box"; "the cat in the hat." But isn't there a limit to this strategy? Would five sentences be as easy to remember for a short time as five single words? No. As the size of any individual chunk increases, the number of chunks that can be held in STM declines (Fendrich & Arengo, 2004). STM can easily handle five unrelated letters or words at once, but five unrelated sentences are much harder to remember.
Keep in mind that STM usually has to perform more than one task at a time. During the brief moments you spent memorizing the preceding rows of letters, you probably gave them your full attention. But normally you have to attend to new incoming information while you work on whatever is already present in short-term memory. Competition between these two tasks for the limited work space in STM means that neither task will be done as well as it could be. Try counting backward from 100 while trying to learn the rows of letters in our earlier example. What happens?
Now turn on some music and try to learn the rows of letters. You'll find that the music doesn't interfere as much, if at all, with learning the letters. Interestingly, when two memory tasks are presented in different sensory modalities (for instance, visual and auditory), they are less likely to interfere with each other than if they are in the same modality (Lehnert & Zimmer, 2008). This suggests the existence of domain-specific working memory systems that can operate at the same time with very little interference.
Not surprisingly, stress and worry have also been shown to be detrimental to the operation of short-term memory (Matthews & Campbell, 2010). This is particularly true when the task at hand involves mathematics, because the worry created by stress competes for working memory space, which would otherwise be allocated to solving the math problem (Beilock, 2008).
Encoding in STM
We encode verbal information for storage in STM phonologically - that is, according to how it sounds. This is the case even if we see the word, letter, or number on a page, rather than hear it spoken (Vallar, 2006). We know this because numerous experiments have shown that when people try to retrieve material from STM, they generally mix up items that sound alike. A list of words such as mad, man, mat, cap is harder for most people to recall accurately than is a list such as pit, day, cow, bar (Baddeley, 1986).
But not all material in short-term memory is stored phonologically. At least some material is stored in visual form, and other information is retained on the basis of its meaning (R. G. Morrison, 2005). For example, we don't have to convert visual data such as maps, diagrams, and paintings into sound before we can code them into STM and think about them. Moreover, research has shown that memory for images is generally better than memory for words because we often store images both phonologically and as images, while words are usually stored only phonologically. The dual coding of images accounts for the reason it is sometimes helpful to form a mental picture of something you are trying to learn (Paivio, 2007).
Maintaining STM
As we have said, short-term memories are fleeting, generally lasting a matter of seconds. However, we can hold information in STM for longer periods through rote rehearsal, also called maintenance rehearsal. Rote rehearsal consists of repeating information over and over, silently or out loud. Although it may not be the most efficient way to remember something permanently, it can be quite effective for a short time.
LONG-TERM MEMORY
Our ability to store vast quantities of information for indefinite periods of time is essential if we are to master complex skills, acquire an education, or remember the personal experiences that contribute to our identity. Everything that we learn is stored in long-term memory (LTM): the words to a popular song; the meaning of justice; how to roller skate or draw a face; your enjoyment of opera or your disgust at the sight of raw oysters; and what you are supposed to be doing tomorrow at 4:00 PM.
Capacity of LTM
We have seen that short-term memory can hold only a few items, normally only for a matter of seconds. By contrast, long-term memory can store a vast amount of information for many years. In one study, for example, adults who had graduated from high school more than 40 years earlier were still able to recognize the names of 75% of their classmates (Lindsay & Read, 2006).
Encoding in LTM
Can you picture the shape of Florida? Do you know what a trumpet sounds like? Can you imagine the smell of a rose or the taste of coffee? Your ability to do most of these things means that at least some long-term memories are coded in terms of nonverbal images: shapes, sounds, smells, tastes, and so on.
Yet, most of the information in LTM seems to be encoded in terms of meaning. If material is especially familiar (the words of the national anthem, for example), you may have stored it verbatim in LTM, and you can often retrieve it word for word when you need it. Generally speaking, however, we do not use verbatim storage in LTM. If someone tells you a long, rambling story, you may listen to every word, but you certainly will not try to remember the story verbatim. Instead, you will extract the main points of the story and try to remember those. Even simple sentences are usually encoded in terms of their meaning. Thus, when people are asked to remember that "Tom called John," they often find it impossible to remember later whether they were told "Tom called John" or "John was called by Tom." They usually remember the meaning of the message, rather than the exact words (R. R. Hunt & Ellis, 2003).
Serial Position Effect
When given a list of items to remember (such as a list of grocery items), people tend to do better at recalling the first items (primary effect) and the last items (recency effect) in the list. They also tend to do poorest of all on the items in the middle of the list.
The explanation for this serial position effect resides in understanding how short- and long-term memory work together. The recency effect occurs because the last items that were presented are still contained in STM and thus are available for recall. The primary effect, on the other hand, reflects the opportunity to rehearse the first few items on the list - increasing their likelihood of being transferred to LTM.
Poor performance occurs on the items in the middle of the list because they were presented too long ago to still be in STM, and because so many items requiring attention were presented before and after them that there was little opportunity for rehearsal. The serial position effect has been shown to occur under a wide variety of conditions and situations (Neath, 1993; Suhr, 2002; W. S. Terry, 2005).
Maintaining LTM
Rote Rehearsal
Rote rehearsal, the principal tool for holding information in STM, is also useful for holding information in LTM. Rote rehearsal is probably the standard method of storing conceptually meaningless material, such as phone numbers, Social Security numbers, security codes, computer passwords, birth dates, and people's names.
Indeed, although everyone hates rote drill, there seems to be no escaping its use in mastering a wide variety of skills, from memorizing the alphabet to playing a work of Mozart on the piano or doing a back flip on a balance beam. Mastering a skill means achieving automaticity, or fluid, immediate performance. Expertise in typing, for example, involves the ability to depress the keys quickly and accurately without thinking about it. Automaticity is achieved only through tedious practice.
Research suggests, however, that repetition without any intention to learn generally has little effect on subsequent recall (Van-Hooff & Golden, 2002).
Elaborative Rehearsal
As we have seen, rote rehearsal with the intent to learn is sometimes useful in storing information in LTM. But often, an even more effective procedure is elaborative rehearsal (Craik, 2002; Craik & Lockhart, 1972), the act of relating new information to something that we already know. Through elaborative rehearsal, you extract the meaning of the new information and then link it to as much of the material already in LTM as possible. We tend to remember meaningful material better than arbitrary facts; and the more links or associations of meaning you can make, the more likely you are to remember the new information later.
Clearly, elaborative rehearsal calls for a deeper and more meaningful processing of new data than does simple rote rehearsal. The Levels of Processing Theory initially proposed by researchers Craik and Lockhart (1972) captures this idea by suggesting that the deeper, more meaningfully and elaborately we process new information, the more likely we are to commit it to memory. Unless we rehearse material in this way, we are likely to soon forget it.
In some situations, special techniques called mnemonics (pronounced as ni-MON-iks) may help you to tie new material to information already in LTM. Some of the simplest mnemonic techniques are the rhymes and jingles that we often use to remember dates and other facts. Thirty days hath September, April, June, and November ... enables us to recall how many days are in a month. With other simple mnemonic devices, words or sentences can be made out of the material to be recalled. We can remember the colors of the visible spectrum - red, orange, yellow, green, blue, indigo, and violet - by using their first letters to form the acronym ROY G. BIV.
Schemata
A variation on the idea of elaborative rehearsal is the concept of schema (plural: schemata). A schema is a mental representation of an event, an object, a situation, a person, a process, or a relationship that is stored in memory and that leads you to expect your experience to be organized in certain ways. For example, you may have a schema for eating in a restaurant, for driving a car, or for attending a class lecture. A class lecture schema might include sitting down in a large room with seats arranged in rows, opening your notebook, and expecting the professor or lecturer to to come in and address the class from the front of the room.
Schemata such as these provide a framework into which incoming information is fitted. Schemata also may color what you recall by prompting you to form a stereotype; that is, to ascribe certain characteristics to all members of a particular group. Thus, becoming aware of your particular schemata is one way to improve your ability to remember.
To summarize, we have seen that the capacity of LTM is immense and material stored there may endure, more or less intact, for decades. By comparison, STM has a sharply limited capacity and information may disappear quickly from it. The sensory registers can take in an enormous volume of information, but they have no ability to process memories. Together, these three stages of memory - the sensory registers, STM, and LTM - comprise the information-processing view of memory.
Types of LTM
The information stored in LTM can take many forms. However, most long-term memories can be classified into one of several types: episodic, semantic, procedural, and emotional memories.
Episodic memories are memories for events experienced in a specific time and place. These are personal memories, rather than historical facts. If you can recall what you ate for dinner last night or how you learned to ride a bike when you were little, then you are calling up episodic memories. Episodic memory is like a diary that lets you go back in time and space to relive a personal experience (Knierim, 2007).
In addition to permitting us to relive past experiences, episodic memories also play a crucial role in our ability to anticipate and envision the future (Schacter & Addis, 2009). That is, by recombining elements of past experiences (episodic memories), we can imagine or simulate future events. For example, in preparation for an important job interview, you would be well served to remember how previous job interviews took place. Then by restructuring the key elements of those past experiences you will be better able to anticipate potential questions and hopefully devise better answers than you may have otherwise. Indeed, some researchers have suggested that even personal goals may emerge as a result of recombining elements of episodic memories to simulate future possibilities and aspirations (D'Argembeau & Mathy, 2011).
Semantic memories are facts and concepts not linked to a particular time. Semantic memory is like a dictionary or encyclopedia, filled with facts and concepts, such as the meaning of the word semantic, the location of the Empire State Building, the value of 2 times 7, and the identity of George Washington.
Procedural memories are motor skills and habits (A. Johnson, 2003). They are not memories about skills and habits; they are the skills and habits. Procedural memories have to do with knowing how: how to ride a bicycle, play a violin, make coffee, write your name, walk across a room, or slam on a car's brakes. The information involved usually consists of a precise sequence of coordinated movements that are often difficult to describe in words. Repetition, and in many cases deliberate practice, are often required to master skills and habits, but once learned, they are rarely completely lost. In addition, research has shown that procedural memories are often strengthened by sleep following the initial acquisition of a skill (Schonauer, Geisler, & Gais, 2014).
Emotional memories are learned emotional responses to various stimuli: all of our loves and hates, our rational and irrational fears, our feelings of disgust and anxiety. If you are afraid of flying insects, become angered at the sight of a Nazi flag, or are ashamed of something you did, you have emotional memories.
Explicit and Implicit Memory
Because of the differences among types of memories, psychologists distinguish between explicit memory, which includes episodic and semantic memories, and implicit memory, which includes procedural and emotional memories. These terms reflect the fact that sometimes we are aware that we know something (explicit memory) and that sometimes we are not aware (implicit memory).
Serious interest in the distinction between explicit and implicit memory began as a result of experiments with amnesic patients.
Additional support for the distinction between explicit and implicit memory is derived from clinical observations of the ways in which strong emotional experiences can affect behavior years later even without any conscious recollection of the experiences (Ohman, 2010; Westen, 1998). In cases of war, abuse, or terrorism, emotional memories are sometimes so overwhelming and painful they can lead to a psychiatric disorder called posttraumatic stress disorder or PTSD (Kekelidze & Portnova, 2011).
The fact that strong emotional memories can affect behavior without conscious awareness seem at first to give credence to Freud's notion of the unconscious mind - that repressed memories for traumatic incidents can still affect our behavior. But implicit memory research suggests instead that people store emotional experiences separately from the memories of the experience itself. Thus, we may feel anxiety about flying because of a traumatic plane ride in early childhood, yet we may not remember the experience that gives rise to that anxiety. Memory of the event is out of reach, not because (as Freud thought) it has been repressed, but because the episodic and emotional components of the experience were stored separately.
Priming
Research on a phenomenon called priming also demonstrates the distinction between explicit and implicit memory. In priming, a person is exposed to a stimulus, usually a word or picture. Later, the person is shown a fragment of the stimulus (a few letters of a word or a piece of a picture) and is asked to complete it. The typical result is that people are more likely to complete fragments with items seen earlier than they are with other, equally plausible items. For example, you might be shown a list of words, including the word tour. Later on, you might be shown a list of word fragments, including _ou_, and be asked to fill in the blanks to make a word. In comparison to others who had not been primed by seeing the word tour, you are far more likely to write tour than you are four, pour, or sour, all of which are just as acceptable as tour. The earlier exposure to tour primes you to write that word.
The Tip-of-the-Tongue Phenomenon
Everyone has had the experience of knowing a word but not quite being able to recall it. This is called the tip-of-the-tongue phenomenon (or TOT) (R. Brown & McNeil, 1966; Hamberger & Seidel, 2003; B. L. Schwartz, 2002; Widner, Otani, & Winkelman, 2005). Although everyone experiences TOTs, these experiences become more frequent during stressful situations (Schwartz, 2010) and as people get older, especially when attempting to recall personal names (Juncos-Rabadan, Facal, Rodriguez, & Pereiro, 2010; Schwartz, 2010; B. L. Schwartz & Frazier, 2005; K. K. White & Abrams, 2002). Moreover, other words - usually with a sound or meaning similar to the word you are seeking - occur to you while you are on the TOT state and thee words interfere with and sabotage your attempt to recall the desired word. The harder you try, the worse the TOT state gets. The best way to recall a blocked word, then, is to stop trying to recall it! Most of the time, the word you were searching for will pop into your head, minutes or even hours after you stopped consciously searching for it (B. L. Schwartz, 2002).
The distinction between explicit and implicit memories means that some knowledge is literally unconscious. Moreover, as we shall soon see, explicit and implicit memories also seem to involve neural structures and pathways (Meng, 2012; Voss & Paller, 2008). However, memories typically work together. When we remember going to a Chinese restaurant, we recall not only when and where we ate and whom we were with (episodic memory), but also the nature of the food we ate (semantic memory), the skills we learned such as eating with chopsticks (procedural memory), and the embarrassment we felt when we spilled the tea (emotional memory). When we recall events, we typically do not experience these kinds of memories as distinct and separate; rather, they are integrally connected, just as the original experiences were. Whether we will continue to remember the experiences accurately in the future depends to a large extent on what happens in our brain.
THE BIOLOGY OF MEMORY
Research on the biology of memory focuses mainly on the question, How and where are memories stored? Simple as the question is, it has proved enormously difficult to answer and our answers are still not entirely complete.
Current research indicates that memories consist of changes in the synaptic connections among neurons (Kandel, 2001; Stepanyants & Escobar, 2011). When we learn new things, old connections are strengthened. These chemical and structural changes build neural networks that grow over a period of months or years (Abraham & Williams, build neural networks that grow over a period of months or years (Abraham & Williams, 2008; Bekinschtein et al., 2008; Lu, Christian, & Lu, 2008), during which time the number of connections among neurons increases as does the likelihood that cells will excite one another through electrical discharges, a process known as long-term potentiation (LTP).
Although learning takes place in the brain, it is also influenced by events occurring elsewhere in the body. Two hormones in particular, epinephrine and cortisol, have been shown to affect long-term retention, especially for unpleasant experiences (Korol & Gold, 2007). Another hormone found to influence memory is ghrelin. Secreted from the lining of the stomach when it is empty, ghrelin travels to the brain where it primarily stimulates receptors in the hypothalamus to signal hunger. However, some ghrelin also finds its way to the hippocampus, where studies with mice have shown it can enhance learning and memory (Diano et al., 2006; Olszewski, Schioth, & Levine, 2008). As a result, hungry mice are more likely to remember where they have found food in the past.
Where Are Memories Stored?
Memories are not all stored in one place. Instead, our brains appear to depend on a large number of neural networks distributed throughout the brain working in concert to form and store memories (Tsien, 2007). As a general rule, however, studies have shown that the areas of the brain involved in encoding a particular event are reactivated when the event is remembered. This suggests that "...the process of remembering an episode involves literally returning to the brain state that was present during that episode" (Danker & Anderson, 2010). This may help explain why, when we have difficulty remembering something, it is often helpful to think about related events or details, thus returning our brain to the initial state we were in when we stored the memory.
Different regions of the brain are specialized for the storage of different kinds of memories. Short-term and working memory, for example, seem to be located primarily in the prefrontal cortex and temporal lobe (Izaki, Takita, & Akema, 2008; Rainer & Miller, 2002; Scheibel & Levin, 2004). Long-term semantic memories seem to be located primarily in the frontal and temporal lobes of the cortex, which interestingly also play a prominent role in consciousness and awareness. Research shows increased activity in a particular area of the left temporal lobe - for example, when people are asked to recall the names of people. A nearby area shows increased activity when they are asked to recall the names of animals, and another neighboring area becomes active when they are asked to recall the names of tools (H. Damasio, Grabowski, Tranel, Hichwa, & Damasio, 1996). Destruction of these areas of the cortex (through head injury, surgery, stroke, or disease) results in selective memory loss (H. Damasio et al., 1996).
Episodic memories also find their home in the frontal and temporal lobes (Jackson, 2004; Nyberg et al., 2003; Stevens & Grady, 2007). But some evidence shows that episodic and semantic memories involve different portions of these brain structures (Prince, Tsukiura, & Cabeza, 2007). In addition, because episodic memories depend on integrating different sensations (vision, audition, and so on) to create a personal memory experience, they also draw upon several distinct sensory areas of the brain (MacKenzie & Donaldson, 2009; Rugg & Vilberg, 2013). Thus, episodic memory is probably best thought of as the integration of memories that are located throughout the brain into a coherent personal experience (D. C. Rubin, 2006).
Procedural memories appear to be located primarily in the cerebellum (an area required for balance and motor coordination) and in the motor cortex (Gabrieli, 1998; Hermann et al., 2004). As you might expect, damage to the cerebellum generally has a negative impact on one's ability to perform specific tasks (Hermann et al., 2004).
Subcortical structures also play a role in long-term memory. For example, the hippocampus has been implicated in the functioning of both semantic and episodic memory (Eichenbaum & Fortin, 2003; Manns, Hopkins, & Squire, 2003), as well as being involved in the ability to remember spatial relationships (Astur, Taylor, Marnelak, Philpott, & Sutherland, 2002; Bilkey & Clearwater, 2005). If the hippocampus is damaged, people can remember events that have just occurred (and are in STM), but their long-term recall of those same events is impaired. The amygdala, a structure that lies near the hippocampus, seems to play a role in emotional memory that is similar to the role the hippocampus plays in episodic, semantic, and procedural memory (LaBar, 2007; Payne et al., 2006; Vermetten & Bremner, 2002). For example, damage to the amygdala reduces the ability to recall new emotional experiences, but it does not prevent the recall of emotional events that occurred prior to the damage, though they are often remembered as neutral facts, devoid of emotional content. This may explain why people with amygdala damage are sometimes unable to "read" facial expressions, even though they recognize the person's face (Pegna, Caldara-Schnetzer, & Khateb, 2008; Pegna, Khateb, & Lazeyras, 2005).
The Role of Sleep
Sleep appears to play an important role in the formation of new memories. For example, a study with adolescents showed that sleeping less than 8 hours a night had a negative impact on working memory (Gradisar, Terrill, Johnston, & Douglas, 2008). Similarly, a study of procedural memory with musicians showed that adequate sleep following practice resulted in improved memory and performance (Allen, 2008). Even remembering to execute a goal or task, such as remembering an appointment or to take medication, is improved following a period of sleep compared to a period of wakefulness (Scullin & McDaniel, 2010).
Studies like this have prompted neuroscientists to explore precisely how sleep is involved in the formation and storage of new memories (Rasch & Born, 2008). Brain imaging with animals and humans shows that the same hippocampal neurons and patterns of neuron activity that accompany initial learning are reactivated during subsequent deep sleep. Thus, it is not surprising that deep sleep after learning serves to strengthen new memories (M. P. Walker & Stickgold, 2006). In particular, sleep appears to selectively enhance our ability to remember emotionally important experiences (Payne & Kensinger, 2010). Not surprisingly, research has also shown that sleep deprivation interferes with the process of long-term potentiation precisely in the regions of the brain involved in memory consolidation (Zagaar, Dao, Levine, Alhaider & Alkadhi, 2013; Suer, Dolu, Artis, Sahin, Yilmaz, & Cetin, 2011). Clearly, psychologists have a long way to go before they will fully understand the biology of memory, but progress is being made in this fascinating area.
FORGETTING
Why do memories, once formed, not remain forever in the brain? Part of the answer has to do with the biology of memory, and another part has to do with the experiences that we have before and after learning.
The Biology of Forgetting
According to the decay theory, memories deteriorate because of the passage of time. Most of the evidence for supporting decay theory comes from experiments known as distractor studies. For example, in one experiment, participants learned a sequence of letters, such as PSQ. Then they were given a three-digit number, such as 167, and asked to count backwards by threes: 167, 164, 161, and so on, for up to 18 seconds (L. R. Peterson & Peterson, 1959). At the end of that period, they were asked to recall the three letters. The results of this test astonished the experimenters. The participants showed a rapid decline in their ability to remember the letters. Because the researchers assumed that counting backwards would not interfere with remembering, they could only account for the forgotten letters by noting that they had simply faded from short-term memory in a matter of seconds. Decay, then, seems to be at least partly responsible for forgetting in short-term memory.
Information in LTM also can be lost if the storage process is disrupted. Head injuries often result in retrograde amnesia, a condition in which people cannot remember what happened to them shortly before their injury. In such cases, forgetting may occur because memories are not fully consolidated in the brain.
Severe memory loss is invariably traced to brain damage caused by accidents, surgery, poor diet, or disease (Roncadin, Guger, Archibald, Barnes, & Dennis, 2004). For example, chronic alcoholism can lead to a form of amnesia called Korsakoff's syndrome caused by a vitamin deficiency in the nutritionally poor diet that is typical of people who abuse alcohol (Brand, 2007). Other studies show the importance of the hippocampus to long-term memory formation (Winocur, Sekeres, Binns, & Moscovitch, 2013). Studies of elderly people who have trouble remembering names, for instance, show alterations in hippocampal functioning and connectivity to other areas of the brain (Tsukiura et al., 2011). Brain scans also reveal hippocampus damage in people suffering from Alzheimer's disease, a neurological disorder that causes severe memory loss (Sankari, Adeli, & Adeli, 2011).
Alzheimer's may also involve below-normal levels of the neurotransmitter acetylcholine in the brain. Indeed, some research suggests that drugs and surgical procedures that increase acetylcholine levels may serve as effective treatments for age-related memory problems (Penner, Rupsingh, Smith, Wells, Borrie, & Bartha, 2010).
Experience and Forgetting
Although sometimes caused by biological factors, forgetting can also result from inadequate learning. A lack of attention to critical cues, for example, is a cause of forgetting commonly referred to as absentmindedness. For example, if you can't remember where you parked your car, most likely you can't remember because you didn't pay attention to where you parked it.
Forgetting also occurs because, although we have attended to the matter to be recalled, we did not rehearse the material enough. Merely "going through the motions" of rehearsal does little good. Prolonged, intense practice results in less forgetting than a few, halfhearted repetitions. Elaborative rehearsal can also help make new memories more durable. When you park your car in space G-47, you will become more likely to remember its location if you think, "G-47. My uncle George is about 47 years old." In short, we cannot expect to remember information for long if we have not learned it well in the first place.
Interference
Inadequate learning accounts for many memory failures, but learning itself can cause forgetting. This is the case because learning one thing can interfere with learning another. Information gets mixed up with, or pushed aside by, other information and thus becomes harder to remember. Such forgetting is said to be due to interference. There are two kinds of interference. In retroactive interference, new material interferes with information already in long-term memory. Retroactive interference occurs every day. For example, once you learn a new telephone number, you may find it difficult to remember your old number, even though you used that old number for years.
In the second kind of interference, proactive interference, old material interferes with new material being learned. Like retroactive interference, proactive interference is an everyday phenomenon. Suppose you always park your car in the lot behind the building where you work, but one day all those spaces are full, so you have to park across the street. When you leave for the day, you are likely to head for the lot behind the building - and may even be surprised that your car is not there. Learning to look for your car behind the building has interfered with your memory that today you parked the car across the street.
The most important factor in determining the degree of interference is the similarity of the competing items. Learning to swing a golf club may interfere with your ability to hit a baseball, but probably won't affect your ability to make a free throw on the basketball courts. The more dissimilar something is from other things that you have already learned, the less likely it will be to mingle and interfere with other material in memory (G. H. Bower & Mann, 1992).
Situational Factors
Whenever we try to memorize something, we are also unintentionally picking up information about the context in which learning is taking place. That information becomes useful when we later try to retrieve the corresponding information from LTM. If those environmental cues are absent when we try to recall what we learned, the effort to remember is often unsuccessful. Context-dependent memory effects tend to be small, so studying in the same classroom where you are scheduled to take an exam will probably not do too much to improve your grade. Nevertheless, contextual cues are occasionally used by police who sometimes take witnesses back to the scene of a crime in the hope that they will recall crucial details that can be used to solve the crime.
Our ability to accurately recall information is also affected by internal cues, a phenomenon known as state-dependent memory. Researchers have found that people who learn material in a particular psychological state tend to recall that material better if they return to the same state they were in during the learning (de-I'Etoile, 2002; Kelemen & Creeley, 2003; Riccio, Millin, & Gisquet-Verrier, 2003). For example, if people learn material while under the influence of caffeine, recall of the material is slightly improved when they are again under the influence of caffeine (Kelemen & Creeley, 2003).
The Reconstructive Process
Forgetting also occurs because of what is called the "reconstructive" nature of remembering. We talked about how schemata are used in storing information in long-term memory. Bartlett proposed that people also use schemata to "reconstruct" memories (Bartlett, 1932). This reconstructive process can lead to huge errors. Indeed, we are sometimes more likely to recall events that never happened than events that actually took place (Brainerd & Reyna, 1998)! The original memory is not destroyed; instead, people are sometimes unable to tell the difference between what actually happened and what they merely heard about or imagined (Neuschatz, Lampinen, Toglia, Payne, & Cisernos, 2007).
We may also reconstruct memories for social reasons or personal self-defense (Feeney & Cassidy, 2003). Each time you tell someone the story of an incident, you may unconsciously make subtle changes in the details of the story. Consequently, these changes become part of your memory of the event. When an experience doesn't fit our view of the world or ourselves, we tend, unconsciously, to adjust it or to blot it out of memory altogether (Bremner & Marmar, 1998).
SPECIAL TOPICS IN MEMORY
Now that we have reviewed the various types of memory and how our memory for different events is stored in the brain, we will turn our attention to some special factors that affect memory.
Cultural Influences
Remembering has practical consequences for our daily life and takes place within a particular context. It's not surprising, then, that many researchers believe that the physical environments, values, self-views, and customs of a given culture have a profound effect on what and how easily people remember (Ross & Wang, 2010). In many Western cultures, for example, being able to recite a long list of words or numbers, to repeat the details of a scene, and to provide facts and figures about historical events are all signs of a "good memory." In fact, tasks such as these are often used to test people's memory abilities. However, these kinds of memory tasks do not necessarily reflect the type of learning, memorization, and categorization skills taught in non-Western schools. Members of other cultures often perform poorly on such memory tests because the exercises seem so odd to them.
In contrast, consider the memory skills of a person living in a society in which cultural information is passed on from one generation to the next through a rich oral tradition. Such an individual may be able to recite the deeds of the culture's heroes in verse or rattle off the lines of descent of families, larger lineage groups, and elders. Or perhaps the individual has a storehouse of information about the migration of animals or the life cycles of plants that help people to obtain food and to know when to harvest crops.
Studies have also shown that culture affects not just our musical preferences, but also out ability to remember and detect small changes in music. Young Japanese children, for example, are better at detecting small variations in pitch of familiar television theme shows than are Canadian children of the same age. Researchers speculate the superior performance of the Japanese children on this task is due to the role that pitch plays in distinguishing different accents in the Japanese language (Trehub, Schellenberg, & Nakata, 2008). In addition, cross-cultural brain imaging research has shown that different regions of the brain are activated when recognizing and remembering music from one's own culture compared to the music of an unfamiliar culture (Demorest et al., 2010).
Autobiographical Memory
Autobiographical memory refers to our recollection of events that happened in our life and when those events took place; as such, it is a form of episodic memory. As Martin Conway (1996) contends, "autobiographical memory is central to self, to identity, to emotional experience, and to all those attributes that define an individual."
In general, recent life events are, of course, easier to recall than earlier ones. In a classic study of autobiographical memory, researchers asked young adults to report the earliest personal memory that came to mind when they saw each of 20 words and then to estimate how long ago each event had occurred. The words were all common nouns, such as hall and oven, for which people can easily create images. In general, most personal memories concerned relatively recent events: The longer ago an event occurred, the less likely people were to report it (Crovitz & Schiffman, 1974). Other research, however, shows that people over age 50 are more likely than younger people to recall events from relatively early in life, probably because many of the most critical choices we make in our lives occur in late adolescence and early adulthood (Janssen, Chessa, & Murre, 2005; Mackavey, Malley, & Stewart, 1991).
Exactly how the vast amount of autobiographical information stored in memory is organized is not fully understood, but research in this area has supported two interesting theories. It may be that we store autobiographical information according to important events in our lives, such as beginning college, getting married, or experiencing the death of a loved one. This view explains why we can usually remember when events occurred relative to these major landmarks in our lives (Shum, 1998). We may also store autobiographical memories in event clusters, which are groups of memories on a related theme or that take place close together in time (N. R. Brown, 2005). However, it is important to remember that like all memory, autobiographical memory is not always accurate, though its accuracy does increase when distinctive cues are present to help elicit the recall of information (McDonough & Gallo, 2008).
Extraordinary Memory
Some people are able to perform truly amazing feats of memory. From time to time, the newspaper will carry a report of a person with a "photographic memory." This phenomenon, called eidetic imagery, enables people to see the features of an image in minute detail, sometimes even to recite an entire page of a book they read only once.
One study screened 500 elementary schoolchildren before finding 20 with eidetic imagery (Haber, 1969). The children were told to scan a picture for 30 seconds, moving their eyes to see all its various parts. The picture was then removed, and the children were told to look at a blank easel and report what they saw in an eidetic image. They needed at least 3 to 5 seconds of scanning to produce an image, even when the picture was familiar. In addition, the quality of eidetic imagery seemed to vary from child to child. One girl in this study could move and reverse images and recall them several weeks later. Three children could produce eidetic images of three-dimensional objects; and some could superimpose an eidetic image of one picture onto another and form a new picture. However, the children with eidetic imagery performed no better than their noneidetic classmates on other tests of memory.
One of the most famous documented cases of extraordinary memory comes from the work of the distinguished psychologist Alexander Luria (Luria & Solotaroff, 1987). For over 20 years, Luria studied a Russian newspaper reporter named Shereshevskii ("S"). In The Mind of a Mnemonist (1968), Luria described how "S" could recall masses of senseless trivia as well as detailed mathematical formulas and complex arrays of numbers. He could easily repeat lists of up to 70 words or numbers after having heard or seen them only once.
"S" and other people with exceptional memories were not born with a special gift for remembering things. Rather, they have carefully developed memory techniques using certain principles. For example, Luria discovered that when "S" might visualize a well-know street, specifically associating each word with some object along the way. When asked to recite the lists of words, he would take an imaginary walk down that street, recalling each object and the word associated with it. By organizing his data in a way that was meaningful to him, he could more easily link them to existing material in his long-term memory.
Developing an exceptional memory takes time and effort (Takahashi, Shimizu, Saito, & Tomoyori, 2006). Mnemonists (pronounced nee-MON-ists), people who are highly skilled at using memory techniques, frequently have compelling reasons for developing their memories. "S" used his memory skills to his advantage as a newspaper reporter. Chess masters also sometimes display astonishing recall of meaningful chessboard configurations.
Flashbulb Memories
A flashbulb memory is the experience of remembering vividly a certain event and the incidents surrounding it even after a long time has passed. We often remember events that are shocking or otherwise highly significant in this way (Cubelli & Della Sala, 2008; Wooffitt, 2005). The death of a close relative, a birth, a graduation, or a wedding day may all elicit flashbulb memories. So can dramatic events in which we were not personally involved, such as the attacks on the World Trade Center and the Pentagon on September 11, 2001 (Edery & Nachson, 2004; Talarico & Rubin, 2003): 97% of Americans surveyed 1 year after the September 11 attacks claimed they could remember exactly where they were and what they were doing when they first heard about the attacks (Pew Research Center for the People and the Press, 2002).
The assumptions that flashbulb memories are accurate, that they form at the time of an event, and that we remember them better because of their highly emotional content have all been questioned (Cubelli & Della Sala, 2013; Lanciano, Curci, & Semin, 2010). First, flashbulb memories are certainly not always accurate. Although this is a difficult contention to test, let's consider just one case. Psychologist Ulric Neisser vividly recalled what he was doing on the day in 1941 when the Japanese bombed Pearl Harbor. He clearly remembered that he was listening to a professional baseball game on the radio, which was interrupted by the shocking announcement. But professional baseball is not played in December, when the attack took place, so this sharp flashbulb memory was simply incorrect (Neisser, 1982).
Even if an event is registered accurately, it may undergo periodic revision, just like other long-term memories (Cubelli & Della Sala, 2008). We are bound to discuss and rethink a major event many times, and we probably also hear a great deal of additional information about that event in the weeks and months after it occurs. As a result, the flashbulb memory may undergo reconstruction and become less accurate over the years until it sometimes bears little or no resemblance to what actually happened.
Eyewitness Testimony
I know what I saw! When an eyewitness to a crime gives evidence in court, the testimony often overwhelms evidence to the contrary. Faced with conflicting or ambiguous testimony, jurors tend to put their faith in people who saw an event with their own eyes. However, there is now compelling evidence that this faith in eyewitnesses is often misplaced.
For more than four decades, Elizabeth Loftus (1993, 2013; Loftus & Pickrell, 1995) has been the most influential researcher into eyewitness memory. In a classic study, Loftus and Palmer (1974) showed experimental participants a film depicting a traffic accident. Some of the participants were asked, "About how fast were the cars going when they hit each other?" Other participants were asked the same question, but with the words smashed into, collided with, bumped into, or contacted in place of hit. The researchers discovered that people's reports of the cars' speeds depended on which word was inserted in the question. Those asked about cars that "smashed into" each other reported that the cars were going faster than those who were asked about cars that "contacted" each other. In another experiment, the participants were also shown a film of a collision and then were asked either "How fast were the cars going when they hit each other?" or "How fast were the cars going when they smashed into each other?" One week later, they were asked some additional questions about the accident that they had seen on film the week before. One of the questions was "Did you see any broken glass?" More of the participants who had been asked about cars that had "smashed into" each other reported that they had seen broken glass than did participants who had been asked the speed of the cars that "hit" each other. These findings illustrate how police, lawyers, and other investigators may, often unconsciously, sway witnesses and influence subsequent eyewitness accounts. On the basis of experiments like these, Loftus and Palmer concluded that eyewitness testimony is unreliable.
So why do eyewitnesses make mistakes?
Whatever the reason for eyewitness errors, there is good evidence that such mistakes can send thousands of innocent people to jail each year in the United States (Pezdek, 2007). For example, based almost entirely on the eyewitness identification testimony of a single individual, Steven Avery was convicted of brutally attacking, raping, and nearly killing a woman in 1985 and was sentenced to 32 years in prison. Although Avery offered alibis from 14 witnesses and documentation showing he wasn't at the scene of a crime, it took repeated legal challenges and new advances in DNA testing for him to overcome the conviction. Finally, on September 11, 2003, Mr. Avery was exonerated of all charges and released from prison. Increasingly, courts are recognizing the limits of eyewitness testimony and are taking steps to teach jurors how to properly evaluate it (Martire & Kemp, 2011).
Recovered Memories
In recent years, a controversy has raged, both within the academic community and in society at large, about the validity of recovered memories (Geraerts, Raymaekers, & Merckelbach, 2010; Gleaves, Smith, Butler, Spiegel, & Kihlstrom, 2010; Porter, Peace, Douglas, & Douchette, 2012). The idea is that people experience an event, then lose all memory of it, and then later recall it, often in the course of psychotherapy or under hypnosis. Frequently, the recovered memories concern physical or sexual abuse during childhood. The issue is important not only for theoretical reasons, but also because of the fact that people have been imprisoned for abuse solely on the basis of the recovered memories of their "victims" (Geraerts, Raymaekers, & Merckelbach, 2008). Adding to this confusion is research that show's children's memories are particularly influenced by negative emotions. Thus, when recalling events associated with an uncomfortable experience, such as abuse, children are more likely to make factual errors than when recalling neutral or positive events (Brainerd, Stein, Silveira, Rohenkold, & Reyna, 2008). No one denies the reality of childhood abuse or the damage that such experiences cause. But are the recovered memories real? Did the remembered abuse really occur?
The answer is by no means obvious. There is ample evidence that people can be induced to "remember" events that never happened (Saletan, 2010; S. M. Smith et al., 2003). Research confirms that it is relatively easy to implant memories of an experience by merely asking about it. Sometimes these memories become quite real to the participant. In one experiment, 25% of adults "remembered" fictitious events by the third time they were interviewed about them. One of the fictitious events involved knocking over a punch bowl onto the parents of the bride at a wedding reception. At the first interview, one participant said that she had no recollection whatsoever of the event; by the second interview, she "remembered" that the reception was outdoors and that she had knocked over the bowl while running around. Some people even "remembered" details about the event, such as what people looked like and what they wore. Yet, the researchers documented that these events never happened (Hyman, Husband, & Billings, 1995).
The implication of this and similar research is that it is quite possible for people to "remember" abusive experiences that never happened. And some people who have "recovered" abuse memories have later realized that the events never occurred. Some of these people have brought suit against the therapists who, they came to believe, implanted the memories. In one case, a woman won such a suit and was awarded $850,000 (Imrie, 1999; also see Geraerts, Raymaekers, & Merckelbach, 2008).
However, there is reason to believe that not all recovered memories are merely the products of suggestion. There are numerous case studies of people who have lived through traumatic experiences, including natural disasters, accidents, combat, assault, and rape, who then apparently forgot these events for many years, but who later remembered them. For example, Wilbur J. Scott, a sociologist, claimed to remember nothing of his tour of duty in Vietnam during 1968-1969, but during a divorce in 1983, he discovered his medals and souvenirs from Vietnam, and the memories then came back to him (Arrigo & Pezdek, 1997).
What is needed is a reliable way of separating real memories from false ones, but so far no such test is available (Bernstein & Loftus, 2009). The sincerity and conviction of the person who "remembers" long-forgotten childhood abuse is no indication of the reality of that abuse. However, evidence does suggest that people who recover memories during suggestive therapy are at an increased risk of fabricating false memories compared to individuals who spontaneously recover memories of abuse (Geraerts et al., 2009). Nevertheless, we are left with the conclusion that recovered memories are not, in themselves, sufficiently trustworthy to justify criminal convictions. There must also be corroborative evidence, since without corroboration, there is no way that even the most experienced examiner can separate real memories from false ones (Loftus, Garry, & Hayne, 2008).