8-15 Why do we forget?

Amid all the applause for memory—all the efforts to understand it, all the books on how to improve it—have any voices been heard in praise of forgetting? William James (1890, p. 680) was such a voice: “If we remembered everything, we should on most occasions be as ill off as if we remembered nothing.” To discard the clutter of useless or out-of-date information—where we parked the car yesterday, our old phone number, restaurant orders already cooked and served—is surely a blessing. The Russian memory whiz S, whom we met at the beginning of this chapter, was haunted by his junk heap of memories. They dominated his consciousness. He had difficulty thinking abstractly—generalizing, organizing, evaluating. After reading a story, he could recite it but would struggle to summarize its gist.

A more recent case of a life overtaken by memory is “A. J.,” whose experience has been studied and verified by a University of California at Irvine research team, along with several dozen other “highly superior autobiographical memory” cases (McGaugh & LePort, 2014; Parker et al., 2006). A. J., who has identified herself as Jill Price, compares her memory to “a running movie that never stops. It’s like a split screen. I’ll be talking to someone and seeing something else…. Whenever I see a date flash on the television (or anywhere for that matter) I automatically go back to that day and remember where I was, what I was doing, what day it fell on, and on and on and on and on. It is nonstop, uncontrollable, and totally exhausting.” A good memory is helpful, but so is the ability to forget. If a memory-enhancing pill becomes available, it had better not be too effective.

More often, however, our unpredictable memory dismays and frustrates us. Memories are quirky. My [DM] own memory can easily call up such episodes as that wonderful first kiss with the woman I love, or trivial facts like the air mileage from London to Detroit. Then it abandons me when I discover I have failed to encode, store, or retrieve a student’s name or where I left my sunglasses.

For some, memory loss is severe and permanent. Consider Henry Molaison (known as “H. M.,” 1926–2008). For 55 years after the removal of much of his hippocampus to stop severe seizures, Molaison was unable to form new conscious memories. He was, as before his surgery, intelligent and did daily crossword puzzles. Yet, reported neuroscientist Suzanne Corkin (2005, 2013), “I’ve known H. M. since 1962, and he still doesn’t know who I am.” For about half a minute he could keep something in mind, enough to carry on a conversation. When distracted, he would lose what was just said or what had just occurred. Without the neural tissue for turning new information into long-term memories, he never could name the current president of the United States (Ogden, 2012).

Molaison suffered from anterograde amnesia—he could recall his past, but he could not form new memories. (Those who cannot recall their past—the old information stored in long-term memory—suffer from retrograde amnesia.)

Neurologist Oliver Sacks (1985, pp. 26–27) described another patient, Jimmie, who had anterograde amnesia resulting from brain damage. Jimmie had no memories—thus, no sense of elapsed time—beyond his injury in 1945.

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When Jimmie gave his age as 19, Sacks set a mirror before him: “Look in the mirror and tell me what you see. Is that a 19-year-old looking out from the mirror?”

Jimmie turned ashen, gripped the chair, cursed, then became frantic: “What’s going on? What’s happened to me? Is this a nightmare? Am I crazy? Is this a joke?” When his attention was diverted to some children playing baseball, his panic ended, the dreadful mirror forgotten.

Sacks showed Jimmie a photo from National Geographic. “What is this?” he asked.

“It’s the Moon,” Jimmie replied.

“No, it’s not,” Sacks answered. “It’s a picture of the Earth taken from the Moon.”

“Doc, you’re kidding! Someone would’ve had to get a camera up there!”

“Naturally.”

“Hell! You’re joking—how the hell would you do that?” Jimmie’s wonder was that of a bright young man from 40 years previous reacting with amazement to his travel back to the future.

Careful testing of these unique people reveals something even stranger: Although incapable of recalling new facts or anything they have done recently, Molaison, Jimmie, and others with similar conditions can learn nonverbal tasks. Shown hard-to-find figures in pictures (in the Where’s Waldo? series), they can quickly spot them again later. They can find their way to the bathroom, though without being able to tell you where it is. They can learn to read mirror-image writing or do a jigsaw puzzle, and they have even been taught complicated job skills (Schacter, 1992, 1996; Xu & Corkin, 2001). They can be classically conditioned. However, they do all these things with no awareness of having learned them. “Well, this is strange,” Molaison said, after demonstrating his nondeclarative memory of skillful mirror tracing. “I thought that would be difficult. But it seems as though I’ve done it quite well” (Shapin, 2013).

Molaison and Jimmie lost their ability to form new explicit memories, but their automatic processing ability remained intact. Like Alzheimer’s patients, whose explicit memories for new people and events are lost, they could form new implicit memories (Lustig & Buckner, 2004). These patients can learn how to do something, but they will have no conscious recall of learning their new skill. Such sad cases confirm that we have two distinct memory systems, controlled by different parts of the brain.

For most of us, forgetting is a less drastic process. Let’s consider some of the reasons we forget.

Much of what we sense we never notice, and what we fail to encode, we will never remember (FIGURE 8.16 below). The English novelist and critic C. S. Lewis (1967, p. 107) described the enormity of what we never encode:

Each of us finds that in [our] own life every moment of time is completely filled. [We are] bombarded every second by sensations, emotions, thoughts … nine-tenths of which [we] must simply ignore. The past [is] a roaring cataract of billions upon billions of such moments: Any one of them too complex to grasp in its entirety, and the aggregate beyond all imagination…. At every tick of the clock, in every inhabited part of the world, an unimaginable richness and variety of ‘history’ falls off the world into total oblivion.

Age can affect encoding efficiency. The brain areas that jump into action when young adults encode new information are less responsive in older adults. This slower encoding helps explain age-related memory decline (Grady et al., 1995).

But no matter how young we are, we selectively attend to few of the myriad sights and sounds continually bombarding us. Consider this example: If you live in the United States, you have looked at thousands of pennies in your lifetime. You can surely recall their color and size, but can you recall what the side with the head looks like? If not, let’s make the memory test easier: If you are familiar with U.S. coins, can you, in FIGURE 8.17, just recognize the real thing? Most people cannot (Nickerson & Adams, 1979). Likewise, few British people can draw from memory the details of a one-pence coin (Richardson, 1993). The details of these coins are not very meaningful, nor are they essential for distinguishing them from other coins. Without encoding effort, many potential memories never form.

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Even after encoding something well, we sometimes later forget it. To study the durability of stored memories, Ebbinghaus (1885) learned more lists of nonsense syllables and measured how much he retained when relearning each list, from 20 minutes to 30 days later. The result, confirmed by later experiments, was his famous forgetting curve: The course of forgetting is initially rapid, then levels off with time (FIGURE 8.18; Wixted & Ebbesen, 1991). Harry Bahrick (1984) found a similar forgetting curve for Spanish vocabulary learned in school. Compared with those just completing a high school or college Spanish course, people 3 years out of school had forgotten much of what they had learned (FIGURE 8.19). However, what people remembered then, they still remembered 25 and more years later. Their forgetting had leveled off.

One explanation for these forgetting curves is a gradual fading of the physical memory trace. Cognitive neuroscientists are getting closer to solving the mystery of the physical storage of memory and are increasing our understanding of how memory storage could decay. Like books you can’t find in your campus library, memories may be inaccessible for many reasons. Some were never acquired (not encoded). Others were discarded (stored memories decay). And others are out of reach because we can’t retrieve them.

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Often, forgetting is not memories faded but memories unretrieved. We store in long-term memory what’s important to us or what we’ve rehearsed. But sometimes important events defy our attempts to access them (FIGURE 8.20). How frustrating when a name lies poised on the tip of our tongue, just beyond reach. Given retrieval cues (“It begins with an M”), we may easily retrieve the elusive memory. Retrieval problems contribute to the occasional memory failures of older adults, who more frequently are frustrated by tip-of-the-tongue forgetting (Abrams, 2008; Salthouse & Mandell, 2013).

Do you recall the gist of the second sentence we asked you to remember? If not, does the word shark serve as a retrieval cue? Experiments show that shark (likely what you visualized) more readily retrieves the image you stored than does the sentence’s actual word, fish (Anderson et al., 1976). (The sentence was “The fish attacked the swimmer.”)

But retrieval problems occasionally stem from interference and, perhaps, from motivated forgetting.

Interference As you collect more and more information, your mental attic never fills, but it surely gets cluttered. An ability to tune out clutter helps people to focus, and focusing helps us recall information. Sometimes, however, clutter wins, and new learning and old collide. Proactive (forward-acting) interference occurs when prior learning disrupts your recall of new information. If you buy a new combination lock, your well-rehearsed old combination may interfere with your retrieval of the new one.

Retroactive (backward-acting) interference occurs when new learning disrupts recall of old information. If someone sings new lyrics to the tune of an old song, you may have trouble remembering the original words. It is rather like a second stone tossed in a pond, disrupting the waves rippling out from the first.

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Information presented in the hour before sleep is protected from retroactive interference because the opportunity for interfering events is minimized (Diekelmann & Born, 2010; Nesca & Koulack, 1994). Researchers John Jenkins and Karl Dallenbach (1924) first discovered this in a now-classic experiment. Day after day, two people each learned some nonsense syllables, then tried to recall them after up to eight hours of being awake or asleep at night. As FIGURE 8.21 shows, forgetting occurred more rapidly after being awake and involved with other activities. The investigators surmised that “forgetting is not so much a matter of the decay of old impressions and associations as it is a matter of interference, inhibition, or obliteration of the old by the new” (1924, p. 612).

The hour before sleep is a good time to commit information to memory (Scullin & McDaniel, 2010), though information presented in the seconds just before sleep is seldom remembered (Wyatt & Bootzin, 1994). If you’re considering learning while sleeping, forget it. We have little memory for information played aloud in the room during sleep, although the ears do register it (Wood et al., 1992).

Old and new learning do not always compete with each other, of course. Previously learned information (Latin) often facilitates our learning of new information (French). This phenomenon is called positive transfer.

Motivated Forgetting To remember our past is often to revise it. Years ago, the huge cookie jar in my [DM] kitchen was jammed with freshly baked chocolate chip cookies. Still more were cooling across racks on the counter. Twenty-four hours later, not a crumb was left. Who had taken them? During that time, my wife, three children, and I were the only people in the house. So while memories were still fresh, I conducted a little memory test. Andy admitted wolfing down as many as 20. Peter thought he had eaten 15. Laura guessed she had stuffed her then-6-year-old body with 15 cookies. My wife, Carol, recalled eating 6, and I remembered consuming 15 and taking 18 more to the office. We sheepishly accepted responsibility for 89 cookies. Still, we had not come close; there had been 160.

Why do our memories fail us? This happens in part because memory is an “unreliable, self-serving historian” (Tavris & Aronson, 2007, p. 6). Consider one study, in which researchers told some participants about the benefits of frequent toothbrushing. Those individuals then recalled (more than others did) having frequently brushed their teeth in the preceding two weeks (Ross et al., 1981).

FIGURE 8.22 reminds us that as we process information we filter, alter, or lose much of it. So why were my family and I so far off in our estimates of the cookies we had eaten? Was it an encoding problem? (Did we just not notice what we had eaten?) Was it a storage problem? (Might our memories of cookies, like Ebbinghaus’ memory of nonsense syllables, have melted away almost as fast as the cookies themselves?) Or was the information still intact but not retrievable because it would be embarrassing to remember?²

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Sigmund Freud might have argued that our memory systems self-censored this information. He proposed that we repress painful or unacceptable memories to protect our self-concept and to minimize anxiety. But the repressed memory lingers, he believed, and can be retrieved by some later cue or during therapy. Repression was central to Freud’s psychoanalytic theory of personality and was a popular idea in mid-twentieth century psychology and beyond. One Norwegian study found that educated people tend to believe in repressed memories more than do those with less formal education (Magnussen et al., 2006). In an American study, 81 percent of university students, and 60 to 90 percent of therapists (depending on their perspective), agreed that “traumatic memories are often repressed” (Patihis et al., 2014). Today, however, increasing numbers of memory researchers think repression rarely, if ever, occurs. People succeed in forgetting unwanted neutral information (yesterday’s parking place), but it’s harder to forget emotional events (Payne & Corrigan, 2007). Thus, we may have intrusive memories of the very traumatic experiences we would most like to forget.

8-16 How do misinformation, imagination, and source amnesia influence our memory construction? How do we decide whether a memory is real or false?

Memory is not precise. Like scientists who infer a dinosaur’s appearance from its remains, we infer our past from stored information plus what we later imagined, expected, saw, and heard. We don’t just retrieve memories, we reweave them. Like Wikipedia pages, memories can be continuously revised. When we “replay” a memory, we often replace the original with a slightly modified version (Hardt et al., 2010). (Memory researchers call this reconsolidation.) So, in a sense, said Joseph LeDoux (2009), “your memory is only as good as your last memory. The fewer times you use it, the more pristine it is.” This means that, to some degree, “all memory is false” (Bernstein & Loftus, 2009).

Despite knowing all this, I [DM] recently rewrote my own past. It happened at an international conference, where memory researcher Elizabeth Loftus (2012) was demonstrating how memory works. Loftus showed us a handful of individual faces that we were later to identify, as if in a police lineup. Later, she showed us some pairs of faces, one face we had seen earlier and one we had not, and asked us to identify the one we had seen. But one pair she had slipped in included two new faces, one of which was rather like a face we had seen earlier. Most of us understandably but wrongly identified this face as one we had previously seen. To climax the demonstration, when she showed us the originally seen face and the previously chosen wrong face, most of us picked the wrong face! As a result of our memory reconsolidation, we—an audience of psychologists who should have known better—had replaced the original memory with a false memory.

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Clinical researchers are experimenting with people’s memory reconsolidation. They have people recall a traumatic or negative experience, then disrupt the reconsolidation of that memory with a drug or brief, painless electroconvulsive shock (Kroes et al., 2014; Lonergan, 2013). If, indeed, it becomes possible to erase your memory for a specific traumatic experience—by reactivating your memory and then disrupting its storage—would you wish for this? If brutally assaulted, would you welcome having your memory of the attack and its associated fears deleted?

In more than 200 experiments involving more than 20,000 people, Loftus has shown how eyewitnesses reconstruct their memories after a crime or an accident. In one experiment, two groups of people watched a film clip of a traffic accident and then answered questions about what they had seen (Loftus & Palmer, 1974). Those asked, “About how fast were the cars going when they smashed into each other?” gave higher speed estimates than those asked, “About how fast were the cars going when they hit each other?” A week later, when asked whether they recalled seeing any broken glass, people who had heard smashed were more than twice as likely to report seeing glass fragments (FIGURE 8.23). In fact, the clip showed no broken glass.

In many follow-up experiments around the world, others have witnessed an event, received or not received misleading information about it, and then taken a memory test. The repeated result is a misinformation effect: Exposed to misleading information, we often, though feeling confident, misremember. A yield sign becomes a stop sign, hammers become screwdrivers, Coke cans become peanut cans, breakfast cereal becomes eggs, and a clean-shaven man morphs into a man with a mustache (Loftus et al., 1992).

So powerful is the misinformation effect that it can influence later attitudes and behaviors (Bernstein & Loftus, 2009). One experiment falsely suggested to some Dutch university students that, as children, they became ill after eating spoiled egg salad (Geraerts et al., 2008). After absorbing that suggestion, they were less likely to eat egg salad sandwiches, both immediately and four months later.

Because the misinformation effect happens outside our awareness, it is nearly impossible to sift the suggested ideas out of the larger pool of real memories (Schooler et al., 1986). Perhaps you can recall describing a childhood experience to a friend and filling in memory gaps with reasonable guesses and assumptions. We all do it, and after more retellings, those guessed details—now absorbed into our memories—may feel as real as if we had actually experienced them (Roediger et al., 1993). False memories, like fake diamonds, seem real.

Even repeatedly imagining nonexistent actions and events can create false memories. American and British university students were asked to imagine certain childhood events, such as breaking a window with their hand or having a skin sample removed from a finger. One in four of them later recalled the imagined event as something that had really happened (Garry et al., 1996; Mazzoni & Memon, 2003).

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Digitally altered photos have also produced this imagination inflation. In experiments, researchers have altered photos from a family album to show some family members taking a hot air balloon ride. After viewing these photos (rather than photos showing just the balloon), children reported more false memories and indicated high confidence in those memories. When interviewed several days later, they reported even richer details of their false memories (Strange et al., 2008; Wade et al., 2002).

Misinformation and imagination effects occur partly because visualizing something and actually perceiving it activate similar brain areas (Gonsalves et al., 2004). Imagined events also later seem more familiar, and familiar things seem more real. The more vividly we can imagine things, the more likely they are to become memories (Loftus, 2001; Porter et al., 2000).

In British and Canadian university surveys, nearly one-fourth of students have reported autobiographical memories that they later realized were not accurate (Mazzoni et al., 2010). I [DM] empathize. For decades, my cherished earliest memory was of my parents getting off the bus and walking to our house, bringing my baby brother home from the hospital. When, in middle age, I shared that memory with my father, he assured me they did not bring their newborn home on the Seattle Transit System. The human mind, it seems, comes with built-in Photoshopping software.

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Among the frailest parts of a memory is its source. We may recognize someone but have no idea where we have seen the person. We may dream an event and later be unsure whether it really happened. We may misrecall how we learned about something (Henkel et al., 2000). Psychologists are not immune to the process. Famed child psychologist Jean Piaget was startled as an adult to learn that a vivid, detailed memory from his childhood—a nursemaid’s thwarting his kidnapping—was utterly false. He apparently constructed the memory from repeatedly hearing the story (which his nursemaid, after undergoing a religious conversion, later confessed had never happened). In attributing his “memory” to his own experiences, rather than to his nursemaid’s stories, Piaget exhibited source amnesia (also called source misattribution). Misattribution is at the heart of many false memories. Authors and songwriters sometimes suffer from it. They think an idea came from their own creative imagination, when in fact they are unintentionally plagiarizing something they earlier read or heard.

Debra Poole and Stephen Lindsay (1995, 2001, 2002) demonstrated source amnesia among preschoolers. They had the children interact with “Mr. Science,” who engaged them in activities such as blowing up a balloon with baking soda and vinegar. Three months later, on three successive days, their parents read them a story describing some things the children had experienced with Mr. Science and some they had not. When a new interviewer asked what Mr. Science had done with them—“Did Mr. Science have a machine with ropes to pull?”—4 in 10 children spontaneously recalled him doing things that had happened only in the story.

Source amnesia also helps explain déjà vu (French for “already seen”). Two-thirds of us have experienced this fleeting, eerie sense that “I’ve been in this exact situation before.” It happens most commonly to well-educated, imaginative young adults, especially when tired or stressed (Brown, 2003, 2004a,b; McAneny, 1996). Some wonder, “How could I recognize a situation I’m experiencing for the first time?” Others may think of reincarnation (“I must have experienced this in a previous life”) or precognition (“I viewed this scene in my mind before experiencing it”).

Alan Brown and Elizabeth Marsh (2009) devised an intriguing way to induce déjà vu in the laboratory. They invited participants to view symbols on a computer screen and to report whether they had ever seen them before. What the viewers didn’t know was that these symbols had earlier been subliminally flashed on the screen, too briefly for conscious awareness. The result? Half the participants reported experiencing déjà vu—a sense of familiarity without awareness of why. Brown and Marsh suggest that real-life experiences may include glancing very briefly at a visual scene, looking away without consciously processing it, then looking again—only to feel the uncanny sense of having seen it before.

The key to déjà vu seems to be familiarity with a stimulus without a clear idea of where we encountered it before (Cleary, 2008). Normally, we experience a feeling of familiarity (thanks to temporal lobe processing) before we consciously remember details (thanks to hippocampus and frontal lobe processing). When these functions (and brain regions) are out of sync, we may experience a feeling of familiarity without conscious recall. Our amazing brains try to make sense of such an improbable situation, and we get an eerie feeling that we’re reliving some earlier part of our life. After all, the situation is familiar, even though we have no idea why. Our source amnesia forces us to do our best to make sense of an odd moment.

Because memory is reconstruction as well as reproduction, we can’t be sure whether a memory is real by how real it feels. Much as perceptual illusions may seem like real perceptions, unreal memories feel like real memories.

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False memories can be persistent. Imagine that we were to read aloud a list of words such as candy, sugar, honey, and taste. Later, we ask you to recognize the presented words from a larger list. If you are at all like the people tested by Henry Roediger and Kathleen McDermott (1995), you would err three out of four times—by falsely remembering a nonpresented similar word, such as sweet. We more easily remember the gist than the words themselves.

Memory construction helps explain why about 75 percent of 301 convicts exonerated by later DNA testing had been misjudged based on faulty eyewitness identification (Lilienfeld & Byron, 2013). It explains why “hypnotically refreshed” memories of crimes so easily incorporate errors, some of which originate with the hypnotist’s leading questions (“Did you hear loud noises?”). It explains why dating partners who fell in love have overestimated their first impressions of one another (“It was love at first sight”), while those who broke up underestimated their earlier liking (“We never really clicked”) (McFarland & Ross, 1987). And it explains why people asked how they felt 10 years ago about marijuana or gender issues recalled attitudes closer to their current views than to the views they had actually reported a decade earlier (Markus, 1986). How people feel today tends to be how they recall they have always felt (Mazzoni & Vannucci, 2007).

One research team interviewed 73 ninth-grade boys and then reinterviewed them 35 years later. When asked to recall how they had reported their attitudes, activities, and experiences, most men recalled their ninth-grade statements at a rate no better than chance. Only 1 in 3 now remembered receiving physical punishment, though as ninth-graders 82 percent had said they had (Offer et al., 2000). As George Vaillant (1977, p. 197) noted after following adult lives through time, “It is all too common for caterpillars to become butterflies and then to maintain that in their youth they had been little butterflies. Maturation makes liars of us all.”

8-17 How reliable are young children’s eyewitness descriptions?

If memories can be sincere, yet sincerely wrong, might children’s recollections of sexual abuse be prone to error? “It would be truly awful to ever lose sight of the enormity of child abuse,” observed Stephen Ceci (1993). Yet Ceci and Maggie Bruck’s (1993, 1995) studies of children’s memories have made them aware of how easily children’s memories can be molded. For example, they asked 3-year-olds to show on anatomically correct dolls where a pediatrician had touched them. Of the children who had not received genital examinations, 55 percent pointed to either genital or anal areas.

In other experiments, the researchers studied the effect of suggestive interviewing techniques (Bruck & Ceci, 1999, 2004). In one study, children chose a card from a deck of possible happenings, and an adult then read the card to them. For example, “Think real hard, and tell me if this ever happened to you. Can you remember going to the hospital with a mousetrap on your finger?” In interviews, the same adult repeatedly asked children to think about several real and fictitious events. After 10 weeks of this, a new adult asked the same question. The stunning result: 58 percent of preschoolers produced false (often vivid) stories regarding one or more events they had never experienced (Ceci et al., 1994). Here’s one:

My brother Colin was trying to get Blowtorch [an action figure] from me, and I wouldn’t let him take it from me, so he pushed me into the wood pile where the mousetrap was. And then my finger got caught in it. And then we went to the hospital, and my mommy, daddy, and Colin drove me there, to the hospital in our van, because it was far away. And the doctor put a bandage on this finger.

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Given such detailed stories, professional psychologists who specialize in interviewing children could not reliably separate the real memories from the false ones. Nor could the children themselves. The above child, reminded that his parents had told him several times that the mousetrap incident never happened—that he had imagined it—protested, “But it really did happen. I remember it!” In another experiment, preschoolers merely overheard an erroneous remark that a magician’s missing rabbit had gotten loose in their classroom. Later, when the children were suggestively questioned, 78 percent of them recalled actually seeing the rabbit (Principe et al., 2006). “[The] research leads me to worry about the possibility of false allegations. It is not a tribute to one’s scientific integrity to walk down the middle of the road if the data are more to one side,” said Ceci (1993). (See Thinking Critically About: Repressed or Constructed Memories of Abuse?)

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Children can, however, be accurate eyewitnesses. When questioned about their experiences in neutral words they understood, children often accurately recalled what happened and who did it (Goodman, 2006; Howe, 1997; Pipe, 1996). When interviewers used less suggestive, more effective techniques, even 4- to 5-year-old children produced more accurate recall (Holliday & Albon, 2004; Pipe et al., 2004). Children were especially accurate when they had not talked with involved adults prior to the interview and when their disclosure was made in a first interview with a neutral person who asked nonleading questions.

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8-19 How can you use memory research findings to do better in this and other courses?

Biology’s findings benefit medicine. Botany’s findings benefit agriculture. So, too, can psychology’s research on memory benefit education. Here, for easy reference, is a summary of some research-based suggestions that could help you remember information when you need it. The SQ3R—Survey, Question, Read, Retrieve, Review—study technique used in this book incorporates several of these strategies.

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