The immediate, initial recording of sensory information in the memory system.

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Question to answer: After reading the information about encoding and retrieval, what can you do to change the way you study that will be consistent with the points raised in that section of the chapter?  Explain.

Information Processing and Memory

During the past three decades, memory research has been driven by the "cognitive revolution" in psychology, which views the mind as an information processor. This predominance is reflected in the most influential model of memory, developed by Richard Shiffrin and Richard Atkinson (1969). Their model assumes that memory involves the processing of information in three successive stages: sensory memory, short-term memory, and long-term memory. Sensory memory, also known as the sensory register, is the first stage of memory. In this stage, sensory information from the world around you is taken in by sensory receptors [...] and processed by the central nervous system. Sensory memories last for a brief period—from less than 1 second to several seconds. There are three types of sensory memory that have been studied: iconic (visual), haptic (touch), and echoic (auditory). When you attend to information in sensory memory, it is transferred to short-term memory, which stores it for about 20 seconds unless you maintain it through mental rehearsal—as when you repeat a phone number to yourself long enough to dial it. Information transferred from short-term memory into long-term memory can be stored for up to a lifetime. Your ability to recall old memories indicates that information also passes from long-term memory into short-term memory.

The handling of information at each memory stage has been compared to information processing by a computer, which involves encoding, storage, and retrieval. Encoding is the conversion of information into a form that can be stored in memory. When you strike the keys on a computer keyboard, your actions are translated into a code that the computer understands. Similarly, information in your memory is stored in codes that your brain can process. Storage is the retention of information in memory. Computers typically store information on hard drives or CDs. In human and animal memory, information is stored in the brain. Retrieval is the recovery of information from memory. When you strike certain keys, you provide the computer with cues that make it retrieve the information you desire. Similarly, we often rely on cues to retrieve memories that have been stored in the brain. We are also subject to forgetting—the failure to retrieve information from memory. Forgetting is analogous to the erasing of information on a hard drive. Figure 7.1.1 summarizes this information-processing model of memory. Though some psychologists question the existence of separate information-processing stages for sensory memory, short-term memory, and long-term memory, there is strong evidence in support of them (Cowan, 1988).

Sensory Memory

Think back to the last movie you saw. It was actually a series of frames, each containing a picture slightly different from the one before it. So why did you see smooth motion instead of a rapidly presented series of individual pictures? You did so because of your visual sensory memory, which stores images for up to a second. Visual sensory memory is called iconic memory; an image stored in it is called an icon (from the Greek word for "image"). The movie projector presented the frames at a rate (commonly 24 frames a second) that made each successive frame appear just before the previous one left your iconic memory, blending together the successive images and creating the impression of smooth motion. You can demonstrate iconic memory by rapidly swinging a pen back and forth. Notice how iconic memory lets you see a blurred image of the path taken by the pen. But how much of the information that stimulates our visual receptors is stored in iconic memory? That question inspired the classic experiment discussed in "The Research Process" box.

Auditory sensory memory serves a purpose analogous to that of visual sensory memory, blending together successive pieces of auditory information. Auditory sensory memory is called echoic memory because sounds linger in it. Echoic memory stores information longer than iconic memory does, normally holding sounds for 3 or 4 seconds but perhaps as long as 10 seconds (Samms, Hari, Rif, & Knuutila, 1993). The greater persistence of information in echoic memory lets you perceive speech by blending together successive spoken sounds that you hear (Ardila, Montanes, & Gempeler, 1986). A good demonstration of your echoic memory is when someone says something to you that you do not become aware of until a few seconds after it was said. Suppose that while you are enthralled by a television show a friend asks, "Where did you put the can opener?" After a brief delay, you might say, "What? ... Oh, it's in the drawer to the left of the sink." Researchers have identified a precise region in the primary auditory cortex that processes echoic memories (Lu, Williamson, & Kaufman, 1992).

Tactile sensory memory is based upon the sense of touch. Tactile sensory memory is called haptic memory and might be used when gripping familiar objects or assessing features or textures of novel objects. Information from the sensory receptors in the skin travels along sensory neurons to the spinal cord and ultimately to the somatosensory cortex in the parietal lobe of the brain. Recent evidence has shown that cells in the somatosensory cortex work together with cells in the visual and auditory cortex (Wang et al., 2015; Zhou & Fuster, 2004) to coordinate sensory memory. Studies such as these are helping to clarify the neural mechanisms that coordinate memory.

Based on Sperling's study and subsequent research, we know that sensory memory can store virtually all the information provided by our sensory receptors and that this information fades rapidly (though the fade rate varies among the senses). Nonetheless, we can retain information that is in sensory memory by attending to it and transferring it into short-term memory.

Short-Term Memory

When you pay attention to information in your sensory memory or information retrieved from your long-term memory, the information enters your short-term memory, which has a limited capacity and holds information for about 0.2 to 60 seconds. Because you are paying attention to this sentence, it has entered your short-term memory. In contrast, other information in your sensory memory, such as the feeling of your tongue touching your teeth, will not enter your short-term memory until your attention is directed to it. And note that you are able to comprehend the words in this sentence because you have retrieved their meanings from your long-term memory. Because we use short-term memory to think about information provided by either sensory memory or long-term memory, it also is called working memory. Though some cognitive psychologists prefer to distinguish between short-term memory and working memory (Kail & Hall, 2001), they have yet to agree on the characteristics that would differentiate the two.

Information stored in short-term memory is encoded as sounds or visual images and then manipulated in working memory (Logie, 1999). We typically encode information as sounds—even when the information is visual. This phenomenon was demonstrated in a study in which participants were shown a series of 6 letters and immediately were asked to try to recall them. The participants' errors showed that they more often confused letters that sounded alike (for example, T and C) than letters that looked alike (for example, Q and O). The letters, though presented visually, had been encoded according to their sounds (Conrad, 1962).

In comparison to sensory memory or long-term memory, short-term memory has a relatively small storage capacity. You can demonstrate this for yourself by performing this exercise: Read the following numerals one at a time, and then (without looking at them) write them down in order on a sheet of paper: 6, 3, 9, 1, 4, 6, 5. Next, read the following numerals one at a time and write them down from memory: 5, 8, 1, 3, 9, 2, 8, 6, 3, 1, 7. If you have average short-term memory storage capacity, you were probably able to recall the 7 numbers in the first set but not the 11 numbers in the second set.

The normal limit of seven items in short-term memory was the theme of a famous article by psychologist George Miller (1956) entitled "The Magical Number Seven, Plus or Minus Two." Miller noted that short-term memory can hold, on the average, seven "chunks" of information, with a range of five to nine chunks. His observation has received support from other research studies (Logie, 2012), though some researchers have found that the normal range of capacity is greater than five to nine chunks (H. V. Smith, 1992). A chunk is a meaningful unit of information, such as a date, a word, or an abbreviation. For example, to a college student familiar with American culture, a list that includes the meaningful chunks CBS, NFL, and FBI would be easier to recall than a list that includes the meaningless combinations of letters JOL, OBS, and CWE.

Miller noted that the ability to chunk individual items of information can increase the amount of information stored in short-term memory (Baddeley, 1994). For example, after a 5-second look at the positions of pieces on a chessboard, expert chess players are significantly better than novice chess players at reproducing the positions of the pieces. Chess experts have a greater ability to chunk chess pieces into thousands of familiar configurations (Chase & Simon, 1973). Thus, though chess experts do not store more memory chunks in their short-term memory than novices do, their memory chunks contain more information (Gobet & Simon, 1998).

Given that about 7 chunks is the typical amount of information in short-term memory, how long will it remain stored? Without maintenance rehearsal (that is, without repeating the information to ourselves), we can store information in short-term memory for no more than about 20 seconds. But if we use maintenance rehearsal, we can store it in short-term memory indefinitely. You could use maintenance rehearsal to remember the items on a short grocery list long enough to select each of them at the store.

Early evidence that unrehearsed information in short-term memory lasts perhaps 20 seconds came from a study conducted by Lloyd and Margaret Peterson (1959) in which they orally presented trigrams that consisted of three consonants (for example, VRG) to their participants. Their procedure is presented in Figure 7.1.2. To distract the participants and prevent them from engaging in maintenance rehearsal of the trigrams, immediately after a trigram was presented a light signaled the participant to count backward from a 3-digit number by threes (for example, "657, 654, 651, ..."). Following an interval that varied from 3 seconds to 18 seconds, a light signaled that the participants were to recall the trigram. The longer the interval, the less likely the participants were to recall the trigram. And when the interval was 18 seconds, the participants rarely could recall the trigram. Thus, the results indicated that unrehearsed information normally remains in short-term memory for no longer than about 20 seconds.

Duration of Short-Term Memory. Peterson and Peterson (1959) demonstrated that the information in short-term memory lasts no more than 20 seconds. A warning light signaled that a trial was to begin. The participant then heard a 3-letter trigram and a 3-digit number. To prevent rehearsal of the trigram, the participant counted backward by threes from the number. After a period of 3 to 18 seconds, a light signaled the participant to recall the trigram. The longer the delay between presentation and recall of the trigram, the less likely the participant was to recall it accurately.

Information stored in short-term memory is commonly lost when other information interferes with it. For example, students who study while having the television playing in the background (Armstrong & Chung, 2000) often experience this loss. Background sounds interfere with the material that they have stored in short-term memory and prevent it from reaching long-term memory. Even low-volume irrelevant background sounds can markedly interfere with cognitive performance. Thus, simply turning down the volume will not be as beneficial as turning off the television.

Long-Term Memory

As mentioned earlier, information moves back and forth between short-term memory and long-term memory. Information processing in long-term memory has been compared to the workings of a library. Information in a library is encoded in materials such as books or magazines, stored on shelves in a systematic way, retrieved via cues given by online catalogs, and forgotten when it is misplaced or its computer record is erased. Similarly, information in long-term memory is encoded in several ways, stored in an organized manner, retrieved via cues, and forgotten because of a failure to store it adequately or to use appropriate retrieval cues.

Encoding

William James (1890/1981, Vol. 1, p. 646) noted, "A curious peculiarity of our memory is that things are impressed better by active than by passive repetition." To appreciate James's claim, try to draw the face side of a U.S. penny from memory. Next, look at the drawings of pennies in Figure 7.1.3. Which one is accurate? Even if you have handled thousands of pennies over the years and realize that the front of a penny has a date and a profile of Abraham Lincoln, you probably were unable to draw every detail. And even when presented with several drawings to choose from, you still might have chosen the wrong one. If you had difficulty, you are not alone. A study of adult Americans found that few could draw a penny from memory, and less than half could recognize the correct drawing of one (Nickerson & Adams, 1979).

What accounts for our failure to remember an image that is a common part of everyday life? The answer depends in part on the distinction between maintenance rehearsal and elaborative rehearsal. As noted earlier, in using maintenance rehearsal, we simply hold information in short-term memory without trying to transfer it into long-term memory, as when we remember a phone number just long enough to dial it. In elaborative rehearsal, we actively organize information and integrate it with information already stored in long-term memory, as when studying material from this [reading] for an exam. Though maintenance rehearsal can encode some information (such as the main features of a penny) into long-term memory (Wixted, 1991), elaborative rehearsal encodes more information (such as the exact arrangement of the features of a penny) into long-term memory (Greene, 1987).

You can experience the benefits of elaborative rehearsal when you are confronted by new concepts in a textbook. If you try to understand a concept by integrating it with information already in your long-term memory, you will be more likely to encode the concept firmly into your long-term memory. For example, when the concept "flashbulb memory" was introduced at the beginning of this [reading], you would have been more likely to encode the concept into long-term memory if it provoked you to think about your own flashbulb memories. Elaborative rehearsal also has important practical benefits. In one study, sixth graders who were taught cardiopulmonary resuscitation showed better retention of what they learned if they used elaborative rehearsal (Rivera-Tovar & Jones, 1990).

The superior encoding of information through elaborative rehearsal supports the levels of processing theory of Fergus Craik and Robert Lockhart (1972), which originally was presented as an alternative to the information-processing model of memory. Craik and Lockhart believe that the level, or "depth," at which we process information determines how well it is encoded and, as a result, how well it is encoded in memory (Lockhart & Craik, 1990). When you process information at a shallow level, you attend to its superficial, sensory qualities—as when you use maintenance rehearsal of a telephone number. In contrast, when you process information at a deep level, you attend to its meaning—as when you use elaborative rehearsal of textbook material. Similarly, if you merely listen to the sound of a popular song over and over on the radio—a relatively shallow level of processing—you might recall the melody but not the lyrics. But if you listen to the lyrics and think about their meaning (perhaps even connecting them to personally significant events)—a deeper level of processing—you might recall both the words and the melody. Functional MRI and PET scans have provided support for the levels of processing theory by revealing that different brain regions are more active during shallow information processing than during deeper, more semantic information processing (Nyberg, 2002).

In a study that supported the levels of processing theory, researchers induced participants to process words at different levels by asking them different kinds of questions about each word just before it was flashed on a screen for a fifth of a second (Craik & Tulving, 1975). Imagine that you are replicating the study, and one of the words is bread. You could induce a shallow, visual level of encoding by asking how the word looks—for instance, "Is the word written in capital letters?" You could induce a somewhat deeper, acoustic level of encoding by asking how the word sounds—"Does the word rhyme with head?" And you could induce a much deeper, semantic level of encoding by asking a question related to what the word means—"Does the word fit in the sentence 'The boy used the ___ to make a sandwich'?" After repeating this procedure with several words, you would present participants with a list of words and ask them to identify which of the words had been presented before.

Craik and Tulving (1975) found that the deeper the level at which a word had been encoded, the more likely it was to be correctly identified (see Figure 7.1.4). Thus, the deeper the level at which information is encoded, the better it will be remembered. This conclusion has been supported by research showing that participants exhibited better recognition of previously presented words when they had attended to the words' meanings than when they had attended to the words' sounds (Ferlazzo, Conte, & Gentilomo, 1993). But some research findings indicate that the strength of the levels of processing effect depends on the nature of the material that is being processed in memory (Challis, Velichovsky, & Craik, 1996).

Storage

There are several major viewpoints on the nature of memory storage. Memory researchers look to memory systems, semantic networks, and cognitive schemas to explain the storage of memories.

Memory Systems

According to influential memory researcher Endel Tulving (1985), we store information in two kinds of long-term memory: Procedural memory includes memories of how to perform behaviors, such as making an omelet or using a computer; declarative memory includes memories of facts. Declarative memory and procedural memory also are referred to, respectively, as explicit memory and implicit memory (Schacter, 1992). Implicit memory for odors can influence human behavior, as in a study of adults who performed creative, counting, and mathematical tests in unscented rooms or rooms weakly scented with jasmine or lavender. Though none of the participants reported smelling either odor, the results showed that jasmine hurt performance and lavender helped performance (Degel & Koester, 1999). Research on advertising has found that it can produce effects on both implicit and explicit memory. That is, we may be affected by memories of information that we may not be aware of (Northrup & Mulligan, 2013).

Tulving (1993) subdivides declarative memory into semantic memory and episodic memory. Semantic memory includes memories of general knowledge, such as the definition of an omelet or the components of a personal computer. Episodic memory includes memories of personal experiences tied to particular times and places, such as the last time you made an omelet or used your computer.

Some memory researchers believe that the brain evolved different memory systems for storing these different kinds of memory into declarative memory for facts and events and procedural memory for skills, habits, and conditioned responses (Eichenbaum, 1997). There is evidence that brain-wave activity distinguishes different memory systems. Participants in one study were presented with a series of pairs of words and had to judge whether members of the pairs were related in meaning (semantic memory) or whether they had been presented with specific pairs before (episodic memory). The semantic memory task was associated with an abundance of alpha brain waves, and the episodic memory task was associated with an abundance of slower theta brain waves (Klimesch, 2012).

The main line of evidence in support of multiple memory systems in human beings comes from studies of people with brain damage. For example, either implicit or explicit memory can be intact while the other is impaired (Gabrieli Fleischman, Keane, & Reminger, 1995). In one case study (Schacter, 1983), a victim of Alzheimer's disease, which is a degenerative brain disorder marked by severe memory impairment, was able to play golf (procedural memory) and had good knowledge of the game (semantic memory) but could not find his tee shots (episodic memory). Though semantic memory and episodic memory are both forms of declarative memory, they may involve different brain systems. This conclusion is supported by PET scan studies that have found that different brain regions are involved in the performance of semantic and episodic memory tasks (Viard, Chételat, Lebreton, Desgranges, Landeau, de la Sayette, Eustache, & Piolino, 2011). Figure 7.1.5 illustrates the relationship of the different memory systems.

Nonetheless, some theorists believe that the selective loss of procedural, semantic, or episodic memories does not necessarily mean that we have separate memory systems (Horner, 1990). The question that many memory researchers seek to answer is this: Do different brain systems serve the different kinds of memory, or does a single brain system serve all of them? Regardless of how many memory systems we have, long-term memories must be stored in a systematic way. Unlike short-term memory, in which a few unorganized items of information can be stored and retrieved efficiently, long-term memory requires that millions of pieces of information be stored in an organized rather than arbitrary manner. Otherwise, you might spend years searching your memory until you retrieved the memory you wanted, just as you might spend years searching the Library of Congress for William James's The Principles of Psychology if the library's books were shelved randomly. The better we are at organizing our memories, the better our recall of them is (Bjorklund & Buchanan, 1989). For example, a study of a server who could take 20 complete full-course dinner orders without writing them down found that he did so by quickly categorizing the items into meaningful groupings. When he was prevented from doing so, he was unable to recall all the orders (Ericsson & Polson, 1988).

Semantic Networks

A theory that explains how semantic information is meaningfully organized in long-term memory is the semantic network theory, which assumes that semantic memories are stored as nodes interconnected by links (see Figure 7.1.6). A node is a concept such as "pencil," "green," "uncle," or "cold," and a link is a connection between two concepts. More related nodes have shorter (that is, stronger) links between them. Even young children organize memories into semantic networks. For example, preschool children who enjoy playing with toy dinosaurs and listening to their parents read to them about dinosaurs may organize their knowledge of dinosaurs into semantic networks (Chi & Koeske, 1983). The dinosaurs would be represented as nodes (for example, "Brontosaurus" or "Tyrannosaurus rex"), and their relationships would be represented by links. The retrieval of a dinosaur's name from memory would activate nodes with which it is linked. So, retrieval of Brontosaurus would be more likely to activate nodes that contain the names of other plant-eating dinosaurs than nodes that contain the names of meat-eating dinosaurs, such as Tyrannosaurus rex. Deterioration of semantic networks may help account for the memory and language disruption seen in many people with schizophrenia (Brébion, et al., 2013) or Alzheimer's disease (Chan, Salmon, & De La Pena, 2001).

Cognitive Schemas

An alternative to the semantic network theory of memory organization is schema theory, which is used to explain both episodic memory and semantic memory. Schema theory was put forth decades ago by the English psychologist Frederic Bartlett (1932), who found that long-term memories are stored as parts of schemas. A schema is a cognitive structure that organizes knowledge about an event or an object and that affects the encoding, storage, and retrieval of information related to it (Alba & Hasher, 1983). Examples of schemas include "birthday party," "class clown," and "Caribbean vacation."

In a classic study, Bartlett instructed British college students to read a Native American folktale that told about a warrior fighting ghosts and later to write the story from memory. He found that the participants recalled the theme of the story but added, eliminated, or changed details to fit their own story schemas. For example, the participants added a moral, left out an event, or altered an aspect (such as changing a canoe to a boat). The reconfiguration of details in memory has received some support from more recent experiments (Ahlberg & Sharps, 2002).

Cultural schemas, which include the experiences, conventions, and expectations particular to one's culture, also can influence memory for stories. In a similar study, children from Papua, New Guinea, and the United States were read two fables ("The Boy Who Cried Wolf" and "Stone Soup"). Like the participants in Bartlett's study, the children changed many of the details in their retelling of the stories. Moreover, there were significant cross-cultural differences in the retelling of these stories, which were attributed to cultural differences in story schemas (Invernizzi & Abouzeid, 1995). Schema theory also has been used to explain gender differences in memory. In one study, children were taken to a playroom where they played with toys for 2 minutes. Half the toys were male-stereotyped (e.g., a space shuttle and train), and half were female-stereotyped (e.g., a Barbie doll and a tea set). Later, each child was asked to identify the toys from the playroom from a set of picture cards provided by the experimenter. Though there were no gender differences in the number of items identified, both girls and boys recognized more toys that were traditionally associated with their sex (Cherney & Ryalls, 1999). These results are consistent with studies that have reported similar biases in memory of masculine and feminine behaviors and female and male characters in children's literature (Signorella, Bigler, & Liben, 1997).

Other researchers have begun to investigate the influence of gender schemas on autobiographical memory in adults and children. In a series of studies, Penelope Davis (1999) found that women and girls reported more childhood memories—and accessed these memories more rapidly—than did men and boys. This gender difference was observed for events that were associated with both positive and negative emotions. In other words, female participants were more likely to recall incidents in which they, or others, were happy, sad, or fearful. Moreover, this gender difference also has been observed for everyday life events that are not associated with strong emotions (Seidlitz & Diener, 1998). The results of these studies have been attributed to gender differences in the socialization of emotional expression in men and women that influence the encoding of life events (Bauer, Stennes, & Haight, 2003).

Retrieval

Memory researchers are not only interested in how we encode and store memories but also in how we retrieve them. Psychologists who favor the semantic network theory study the role of spreading activation, and psychologists who favor schema theory study the role of constructive recall.

Spreading Activation

In short, we may search in our memory for forgotten ideas, just as we rummage our house for a lost object. In both cases, we visit what seems to us the probable neighborhood of that which we miss. We turn over the things under which, or within which, or alongside which, it may possibly be; and if it lies near them, it soon comes to view. But these matters, in the case of a mental object sought, are nothing but its associatives. (James, 1890/1981, Vol. 1, p. 615)

The semantic network theory of memory agrees with William James's statement that the retrieval of memories from long-term memory begins by searching a particular region of memory and then tracing the associations among nodes (memories) in that region, rather than by haphazardly searching through information stored in long-term memory. The retrieval of a node from memory stimulates activation of related nodes, so-called spreading activation (Collins & Loftus, 1975). This process is analogous to looking for a book in a library. You would use the online catalog to give you a retrieval cue (a book number) to help you locate the book you want. Similarly, when you are given a memory retrieval cue, the relevant stored memories are activated, which in turn activate memories with which they are linked (Anderson, 1983). In keeping with this phenomenon, advertisers incorporate distinctive retrieval cues in their advertisements for specific products so that the repetition of those cues will evoke recall of those products. For example, a study found that the use of a visual cue helped children recall advertised cereal better and made them more likely to ask their parents to buy the cereal (Macklin, 1994).

To illustrate retrieval from a semantic network, suppose that you were given the cue "sensory memory." If your semantic network were well organized, the cue might activate nodes for "Sperling," "iconic," and "partial report." But if your semantic network were less well organized, the cue might also activate nodes for "amnesia," "chunks," or "Alzheimer's." And if your semantic network were poorly organized, the cue might activate nodes completely unrelated to sensory memory, such as "hallucination," "sensory deprivation," or "extrasensory perception."

Research findings indicate that spreading activation is important in a variety of contexts. The retrieval of mathematical facts depends on spreading activation within an arithmetic memory network (Niedeggen & Roesler, 1999). Word retrieval, as in the case of translation, among bilingual speakers also depends on spreading inactivation with the two language networks (Zhou & Li, 2013). And a study of radiologists found that their ability to make correct diagnoses from X-ray films depended in part on how well their relevant semantic networks facilitated spreading activation (Raufaste, Eyrolle, & Marine, 1998).

Constructive Recall

In contrast to semantic network theory, schema theory assumes that when we retrieve memories we might alter them to make them consistent with our schemas. An example of the schematic nature of memory retrieval, taken from testimony about the 1972 Water-gate burglary that led to the resignation of President Richard Nixon, was provided by the eminent memory researcher Ulric Neisser (1981). Neisser described how a schema influenced the testimony of John Dean, former legal counsel to President Nixon, before the Senate Watergate Investigating Committee in 1973. Dean began his opening testimony with a 245-page statement in which he recalled the details of dozens of meetings that he had attended over a period of several years. Dean's apparently phenomenal recall of minute details prompted Senator Daniel Inouye of Hawaii to ask skeptically, "Have you always had a facility for recalling the details of conversations which took place many months ago?" (Neisser, 1981, p. 1).

Neisser found that Inouye's skepticism was well founded. In comparing Dean's testimony with tape recordings (secretly made by Nixon) of those conversations, Neisser found that Dean's recall of their themes was accurate, but his recall of many of the details was inaccurate. Neisser took this finding as evidence for Dean's reliance on a schema to retrieve memories. The schema reflected Dean's knowledge that there had been a cover-up of the Watergate break-in. Neisser (1984) used this analysis to support his conclusion that, in recalling real-life events, we rely on constructive recall more often than literal recall.

What Neisser called constructive recall is the distortion of memories by adding or changing details to fit a schema (Schacter, Norman, & Koutstaal, 1998). Schemas in the form of scripts for particular events even can affect eyewitness testimony. For example, the scripts we have for different crimes can affect our recall of events related to them. We might recall things that did not actually occur during a robbery if they fit our script for that kind of robbery (Garcia-Bajos & Migueles, 2003). Constructive recall might even explain why honest people have reported being abducted by aliens in UFOs. These people's memories might be constructed from nightmares, media attention, hypnotic suggestions during therapy, and support for their claims by alien-abduction groups (Clancy, 2007). But neither schema theory nor semantic network theory has yet emerged as the best explanation of the storage and retrieval of long-term memories. Perhaps a complete explanation requires both.

Forgetting

According to William James (1890/1981, Vol. 1, p. 640), "If we remembered everything, we should on most occasions be as ill off as if we remembered nothing." James believed that forgetting is adaptive because it rids us of useless information that might impair our recall of useful information. But as you are sometimes painfully aware of when taking exams, even useful information that has been stored in memory is not always retrievable. The inability to retrieve previously stored information is called forgetting.

Measuring Forgetting

The first formal research on forgetting was conducted by the German psychologist Hermann Ebbinghaus (1885/1913). Ebbinghaus (1850-1909) made a purposeful decision to do for the study of memory what Gustav Fechner had done for the study of sensation—subject it to the scientific method (Postman, 1985). Ebbinghaus studied memory by repeating lists of items over and over until he could recall them in order perfectly. The items he used were called nonsense syllables (consisting of a vowel between two consonants, such as VEM) because they were not real words. He used nonsense syllables instead of words because he wanted a "pure" measure of memory, unaffected by prior associations with real words. Despite this effort, he discovered that even nonsense syllables varied in their meaningfulness, depending on how similar they were to words or parts of words.

Ebbinghaus found that immediate recall is worse for items in the middle of a list than for those at the beginning and end of a list (see Figure 7.1.7). This differential forgetting is called the serial-position effect (Korsnes, Magnussen, & Reinvang, 1996). The better memory for items at the beginning of a list is called the primacy effect, and the better memory for items at the end of a list is called the recency effect. Thus, in memorizing a list of terms from this [reading], you would find it harder to memorize terms from the middle of the list than terms from the beginning or end of the list. The serial-position effect can even influence our memory for television commercials. A consumer psychology study demonstrated that when participants watched blocks of television commercials, their recall was worse for commercials in the middle of the blocks than at the beginning (especially) and end of the blocks. Television advertisers need to consider the relative placement of their advertisements for maximum impact on viewers' memories (Pieters & Bijmolt, 1997).

What accounts for the serial-position effect? The primacy effect seems to occur because the items at the beginning of a list are subjected to more rehearsal as a learner memorizes the list, firmly placing those items in long-term memory. And the recency effect seems to occur because items at the end of the list remain readily accessible in short-term memory. In contrast, items in the middle of the list are neither firmly placed in long-term memory nor readily accessible in short-term memory. Note that this explanation supports Shiffrin and Atkinson's distinction between short-term memory and long-term memory. Before Ebbinghaus's work, knowledge of memory was based on common sense, anecdotal reports, and reasoning, with little supporting empirical evidence. Ebbinghaus moved memory from the philosophical realm into the psychological realm, making it subject to scientific research.

Ebbinghaus also introduced the method of savings, which is commonly called relearning, as a way to assess memory. In using the method of savings, Ebbinghaus memorized items in a list until he could recall them perfectly, noting how many trials he needed to achieve perfect recall. After varying intervals, during which he naturally forgot some of the items, Ebbinghaus again memorized the list until he could recall it perfectly. The delay varied from 20 minutes to 31 days. He found that it took him fewer trials to relearn a list than to learn it originally. He called the difference between the number of original trials and the number of relearning trials savings because he relearned the material more quickly the second time. The phenomenon of savings demonstrates that even when we cannot recall information, much of it still remains stored in memory, even though it is inaccessible to recall. If it were not still stored, we would take just as long to relearn material as we took to learn it originally.

When you study for a cumulative final exam, you experience savings. Suppose that your psychology course lasts 15 weeks, and you study your notes and readings for 6 hours a week to perform at an A level on exams given during the semester. You will have studied for a total of 90 hours. If you then studied for a cumulative final exam, you would not have to study for 90 hours to memorize the material to your original level of mastery. In fact, you would have to study for only a few hours to master the material again. Savings occurs because relearning improves the retrieval of information stored in memory (MacLeod, 1988).

Relearning is a method of testing implicit memory because it assesses information that has been retained without necessarily being accessible to conscious awareness prior to relearning. As another example of an implicit memory test, consider the word-stem completion test. Suppose you are exposed in passing to a list of words that includes telephone. Later, despite having no recollection of having seen the word, you would be more likely to take the word stem tele- and form the word telephone than if you had not been exposed to that word earlier.

You are more familiar with tests of explicit memory. A recognition test measures your ability to identify information that you have been exposed to previously when it is presented again. Recognition tests that you might encounter in college include matching, true/false, and multiple-choice exams. A recall test measures your ability to remember information without the information being presented to you. Recall tests that you might encounter in college include essay and fill-in-the-blanks exams. Ebbinghaus also found that once we have mastered a list of items, forgetting is initially rapid and then slows (see Figure 7.1.8). This phenomenon has been replicated many times (Wixted & Ebbesen, 1991). So, if you memorized a list of terms from this [reading] for an exam, you would do most of your forgetting in the first few days after the exam. But in keeping with the concept of levels of processing, meaningless nonsense syllables are initially forgotten more rapidly than is meaningful material, such as psychology terms.

Ebbinghaus's forgetting curve, which shows rapid initial forgetting followed by less and less forgetting over time, even holds for material learned decades before, as demonstrated in a recent study. Participants, aged 11 to 70 years, were former pupils of an elementary school in the Molenberg neighborhood of Heerlen in the Netherlands. Though some of the participants had not lived in the neighborhood for 50 years, they showed surprisingly good retention of the street names. Their forgetting was rapid in the first 5 years after leaving the neighborhood, but then it stabilized for more than 40 years after leaving. After a certain amount of time, memories that have not been forgotten can become permanently held, in a kind of "permastore" (Schmidt et al., 2000).

Explanations of Forgetting

During the past century, psychologists have provided several explanations of forgetting. These include trace decay, interference, motivation, and encoding specificity.

Trace Decay

Plato, anticipating decay theory, likened memory to an imprint made on a block of soft wax: Just as soft-wax imprints disappear over time, memories fade over time. But decay theory has received little research support, and a classic study provided evidence against it. John Jenkins and Karl Dallenbach (1924) had participants memorize a list of 10 nonsense syllables and then either stay awake or immediately go to sleep for 1, 2, 4, or 8 hours. At the end of each period, the participants tried to recall the nonsense syllables. The researchers wondered whether sleep would prevent waking activities from interfering with the memories.

The graph in Figure 7.1.9 shows that participants had better recall if they slept than if they remained awake. There was some memory loss during sleep, providing modest support for decay theory, but if decay theory were an adequate explanation of forgetting, participants should have shown the same level of recall whether they remained awake or slept. Jenkins and Dallenbach concluded that participants forgot more of the nonsense syllables if they remained awake because experiences they had while awake interfered with their memories. In contrast, participants had forgotten fewer nonsense syllables after sleeping because they had few experiences while asleep that could interfere with their memories for the nonsense syllables. The durability of many childhood memories throughout adulthood, such as memories of your childhood neighborhood held in "permastore," also provides evidence against the decay theory.

Interference

Since Jenkins and Dallenbach's classic study contradicting decay theory, psychologists have come to favor interference as a better explanation of forgetting. Interference theory assumes that forgetting results from particular memories' interfering with the retrieval of other memories. Interference occurs, for example, when we try to recall advertisements for the myriad of products we are exposed to in everyday life (Kumar, 2000). In proactive interference, old memories interfere with new memories (if you move to a new home, for instance, your memory of your old phone number might interfere with your ability to recall your new one). Proactive interference has been used to demonstrate that sign language and spoken language may be stored separately in human memory. A study found that there is less proactive interference in memory when old and new materials are each presented in a different language (that is, sign language and spoken language) than if both are presented in the same language (Hoemann & Keske, 1995). In retroactive interference, new memories interfere with old ones (your memory of your new phone number might interfere with your memory of your old one). Retroactive interference explains why learning a second language may interfere with our ability to retrieve words from our first language (Isurin & McDonald, 2001). Figure 7.1.10 illustrates the difference between proactive interference and retroactive interference.

You certainly have experienced both kinds of interference when taking an exam. Material you have studied for other courses sometimes interferes with your memories of the material on the exam. And interference is stronger when the materials are similar. Thus, biology material will interfere more than computer science material with your recall of psychology material. Because of the great amount of material you learn during a semester, proactive interference might be a particularly strong influence on your later exam performance (Dempster, 1985). So it would be best to study different subjects as far apart as possible rather than studying a bit of each every day. Moreover, be sure to study before going to sleep and right before your exam to reduce the effect of retroactive interference on your retrieval of relevant memories during the exam.

Motivation

Sigmund Freud (1901/1965) claimed that we can forget experiences through repression, the process by which emotionally threatening experiences, such as witnessing a murder, are banished to the unconscious mind. Though research findings tend to contradict Freudian repression as an explanation of forgetting (Abrams, 1995), some studies suggest that we are more motivated to forget emotionally upsetting experiences than other kinds of experiences. Yet other studies find that there is no difference in recall of pleasant or unpleasant experiences (Bradley & Baddeley, 1990).

In an experiment that possibly demonstrated motivated forgetting, participants were shown one of two versions of a training film for bank tellers that depicted a simulated bank robbery. In one version, a shot fired by the robbers at pursuers hit a boy in the face. The boy fell to the ground, bleeding profusely. In the other version, instead of showing the boy being shot, the bank manager was shown talking about the robbery. When asked to recall details of the robbery, participants who had seen the violent version had poorer recall of the details of the crime than did participants who had seen the nonviolent version. One possible explanation is that the content of the violent version motivated participants to forget what they had seen (Loftus & Burns, 1982). However, in some cases, memory of traumatic events will be superior to memory of ordinary events (Christianson & Loftus, 1987).

Encoding Specificity

Because the retrieval of long-term memories depends on adequate retrieval cues, forgetting sometimes can be explained by the failure to have or to use those cues. For example, odors that we associate with an event can aid our recall of it (Smith, Standing, & de Man, 1992). This explanation is known as cue-dependence theory. At times we might fail to find an adequate cue to activate the relevant portion of a semantic memory network. Consider the tip-of-the-tongue phenomenon, in which you cannot quite recall a familiar word—though you feel that you know it (Schwartz & Smith, 1997). As a demonstration, you might induce a tip-of-the-tongue experience by trying to recall the names of the seven dwarfs in the Snow White fairy tale. You might fail to recall one or two of them, yet still feel that you know them (Miserandino, 1991). The tip-of-the-tongue phenomenon indicates that when we speak, we might retrieve the meaning of a word before we retrieve its sound pattern (Vigliocco, Vinson, Martin, & Garrett, 1999). The frequency of tip-of-the-tongue experiences and the time that it takes to resolve them by retrieving the correct word increase with age (Heine, Ober, & Shenaut, 1999).

A study of the tip-of-the-tongue phenomenon presented college students with the faces of 50 celebrities and asked them to recall their names. The results indicated that the students searched for the names by using cues associated with the celebrities. The students tried to recall their professions, where they usually performed, and the last time they had seen them. Characteristics of the names also served as cues for recalling them. These cues included the first letters of the names, the first letters of similar-sounding names, and the number of syllables in the names (Yarmey, 1973). This study supports the concept of encoding specificity, which states that recall will be best when cues that were associated with the encoding of a memory are also present during attempts at retrieving the memory (Tulving & Thomson, 1973). Researchers interested in the role of encoding specificity in forgetting study context-dependent memory and state-dependent memory.

Context-Dependent Memory

In an unusual experiment on encoding specificity, scuba divers memorized lists of words while either underwater or on a beach, and then tried to recall the words while either in the same location or in the other location (Godden & Baddeley, 1975). The participants communicated with the experimenter through a special intercom system. The results indicated that when participants memorized and recalled the words in different locations, they recalled about 30 percent fewer than when they memorized and recalled the words in the same location. This tendency for recall to be best when the environmental context present during the encoding of a memory also is present during attempts at retrieving it is known as context-dependent memory. The findings of the study even have practical implications. Instructions given to scuba divers should be given underwater as well as on dry land, and if divers are making observations about what they see underwater, they should record them there and not wait until they get on dry land (Baddeley, 1982).

When you return to your old school or neighborhood, long-lost memories might come flooding back, evoked by environmental cues that you had not been exposed to for years. This effect of environmental context on recall is not lost on theater directors, who hold dress rehearsals in full costume amid the scenery that will be used during actual performances. Similarly, even your academic performance can be affected by environmental cues (Parker & Gellatly, 1997), as in a study in which college students read an article in either noisy or silent conditions and then were tested on their comprehension of it in either noisy or silent conditions (Grant et al., 1998). They performed better when they read the article and were tested under the same conditions (noisy-noisy or silent-silent) than when they did so under different conditions (noisy-silent or silent-noisy). Likewise, college students may perform worse when their exams are given in classrooms other than their normal ones (Abernethy, 1940). Perhaps you have noticed this phenomenon when you have taken a final exam in a strange room. If you find yourself in that situation, you might improve your performance by mentally reinstating the environmental context in which you learned the material (Smith, 1984).

There is controversy among memory researchers about whether the environmental context is important when recall is required but not when recognition is required. In other words, your performance on an essay exam might be impaired if you took the exam in a strange room, but your performance on a multiple-choice test would not. Perhaps tasks that require recognition include enough retrieval cues of their own, making environmental retrieval cues relatively less important (Eich, 1980). But some research indicates that even recognition memory is affected by environmental context. In one study, participants observed a person and then were asked to identify the individual in a photo lineup. Some participants had to identify the individual under the same environmental context, and some under different contexts. Recognition was better under the same context. In fact, participants who simply imagined the original context improved their recognition performance (Smith & Vela, 1992).

State-Dependent Memory

Our recall of memories depends not only on cues from the external environment but also on cues from our internal states. The effect on recall of the similarity between a person's internal state during encoding and during retrieval is called state-dependent memory. For example, memories encoded while the person is in a psychoactive drug-induced state will be recalled better when the person is in that state. A variety of drugs induce state-dependent memory, a fact first noted in 1835 (Overton, 1991). These drugs include alcohol (Nakagawa & Iwasaki, 1996), benzodiazepines (Sanday, Zanin, Patti, Tufkik, & Frussa-Filho, 2012), and barbiturates (Kumar, Ramalingam, & Karanth, 1994). Likewise, people who learn material while exercising on a bicycle ergometer will recall the material better if they do so while exercising on a bicycle ergometer (Miles & Hardman, 1998). Given this phenomenon, perhaps people who discuss business deals during aerobic exercise might have some difficulty recalling what they discussed when they return to their offices.

In a government-sponsored study on the possible state-dependent effects of marijuana (Eich, Weingartner, Stillman, & Gillin, 1975), one group of participants memorized a list of words after smoking marijuana, and a second group memorized the same list after smoking a placebo that tasted like marijuana. Participants were "blind"; that is, they did not know whether they were smoking marijuana or a placebo. Four hours later, half of each group smoked either marijuana or a placebo and then tried to recall the words they had memorized. Recall was better either when participants smoked the placebo on both occasions or when they smoked marijuana on both occasions than when they smoked marijuana on one occasion and the placebo on the other. You should not conclude that marijuana smoking improves memory. [M]arijuana actually impairs memory. And indeed, in this study the group who smoked the placebo on both occasions performed better than the groups who smoked marijuana on either occasion or both occasions.

Our internal states also involve our moods, which can play a role in a form of state-dependent memory called mood-dependent memory, in which our recall of information that has been encoded in a particular mood will be best when we are in that mood again. If you study material while listening to music that evokes a particular mood and then are tested on the material later, you might perform better if you are tested while listening to music that evokes a similar mood (Balch, Myers, & Papotto, 1999). Mood appears to act as a cue for the retrieval of memories. In one study, one group of undergraduates memorized a word list while in a state of fear, and a second group memorized a word list while in a state of relaxation. Recall was better for participants who learned and recalled the word lists in the same emotional state (Robinson & Rollings, 2011). Thus, if you have an emotional experience, you might be more likely to recall details of that experience when you are again experiencing the same emotion.

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