22-1 What is memory, and how is it measured?

Memory is learning that persists over time; it is information that has been acquired and stored and can be retrieved. Research on memory’s extremes has helped us understand how memory works. At age 92, my [DM’s] father suffered a small stroke that had but one peculiar effect. He was as mobile as before. His genial personality was intact. He knew us and enjoyed poring over family photo albums and reminiscing about his past. But he had lost most of his ability to lay down new memories of conversations and everyday episodes. He could not tell me what day of the week it was, or what he’d had for lunch. Told repeatedly of his brother-in-law’s recent death, he was surprised and saddened each time he heard the news.

At the other extreme are people who would be gold medal winners in a memory Olympics. Russian journalist Solomon Shereshevskii, or S, had merely to listen while other reporters scribbled notes (Luria, 1968). We could parrot back a string of about 7—maybe even 9—digits. S could repeat up to 70, if they were read about 3 seconds apart in an otherwise silent room. Moreover, he could recall digits or words backward as easily as forward. His accuracy was unerring, even when recalling a list 15 years later. “Yes, yes,” he might recall. “This was a series you gave me once when we were in your apartment. . . . You were sitting at the table and I in the rocking chair. . . . You were wearing a gray suit. . . .”

Amazing? Yes, but consider your own impressive memory. You remember countless faces, places, and happenings; tastes, smells, and textures; voices, sounds, and songs. In one study, students listened to snippets—a mere four-tenths of a second—from popular songs. How often did they recognize the artist and song? More than 25 percent of the time (Krumhansl, 2010). We often recognize songs as quickly as we recognize a familiar voice.

So, too, with faces and places. Imagine viewing more than 2500 slides of faces and places for 10 seconds each. Later, you see 280 of these slides, paired with others you’ve never seen. Actual participants in this experiment recognized 90 percent of the slides they had viewed in the first round (Haber, 1970). In a follow-up experiment, people exposed to 2800 images for only 3 seconds each spotted the repeats with 82 percent accuracy (Konkle et al., 2010). Some “super-recognizers” display an extraordinary ability to recognize faces. Eighteen months after viewing a video of an armed robbery, one such police officer spotted and arrested the robber walking on a busy street (Davis et al., 2013). And it’s not just humans who have shown remarkable memory for faces (FIGURE 22.1).

How do we accomplish such memory feats? How does our brain pluck information from the world around us and tuck that information away for later use? How can we remember things we have not thought about for years, yet forget the name of someone we met a minute ago? How are memories stored in our brain? Why will you be likely, later in this chapter, to misrecall this sentence: “The angry rioter threw the rock at the window”? In this chapter, we’ll consider these fascinating questions and more, including tips on how we can improve our own memories.

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To a psychologist, evidence that learning persists includes these three measures of retention:

Long after you cannot recall most of the people in your high school graduating class, you may still be able to recognize their yearbook pictures from a photographic lineup and pick their names from a list. In one experiment, people who had graduated 25 years earlier could not recall many of their old classmates. But they could recognize 90 percent of their pictures and names (Bahrick et al., 1975). If you are like most students, you, too, could probably recognize more names of Snow White’s seven dwarfs than you could recall (Miserandino, 1991).

Our recognition memory is impressively quick and vast. “Is your friend wearing a new or old outfit?” “Old.” “Is this five-second movie clip from a film you’ve ever seen?” “Yes.” “Have you ever seen this person before?” “No.” Before the mouth can form our answer to any of millions of such questions, the mind knows, and knows that it knows.

Our response speed when recalling or recognizing information indicates memory strength, as does our speed at relearning. Pioneering memory researcher Hermann Ebbinghaus (1850–1909) showed this over a century ago, using nonsense syllables. He randomly selected a sample of syllables, practiced them, and tested himself. To get a feel for his experiments, rapidly read aloud, eight times over, the following list (from Baddeley, 1982), then look away and try to recall the items:

JIH, BAZ, FUB, YOX, SUJ, XIR, DAX, LEQ, VUM, PID, KEL, WAV, TUV, ZOF, GEK, HIW.

The day after learning such a list, Ebbinghaus could recall few of the syllables. But they weren’t entirely forgotten. As FIGURE 22.2 portrays, the more frequently he repeated the list aloud on Day 1, the less time he required to relearn the list on Day 2. Additional rehearsal (overlearning) of verbal information increases retention, especially when practice is distributed over time. For students, this means that it helps to rehearse course material even after you know it.

The point to remember: Tests of recognition and of time spent relearning demonstrate that we remember more than we can recall.

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22-2 How do psychologists describe the human memory system?

Architects make miniature house models to help clients imagine their future homes. Similarly, psychologists create memory models to help us think about how our brain forms and retrieves memories. An information-processing model likens human memory to computer operations. Thus, to remember any event, we must

Like all analogies, computer models have their limits. Our memories are less literal and more fragile than a computer’s. Moreover, most computers process information sequentially, even while alternating between tasks. Our agile brain processes many things simultaneously (some of them unconsciously) by means of parallel processing.

To focus on multitrack processing, one information-processing model, connectionism, views memories as products of interconnected neural networks. Specific memories arise from particular activation patterns within these networks. Every time you learn something new, your brain’s neural connections change, forming and strengthening pathways that allow you to interact with and learn from your constantly changing environment.

To explain our memory-forming process, Richard Atkinson and Richard Shiffrin (1968) earlier proposed another model, with three stages:

Other psychologists have updated this model (FIGURE 22.3) with important newer concepts, including working memory and automatic processing.

WORKING MEMORY Alan Baddeley and others (Baddeley, 2001, 2002; Barrouillet et al., 2011; Engle, 2002) extended Atkinson and Shiffrin’s view of short-term memory as a small, brief storage space for recent thoughts and experiences. This stage is not just a temporary shelf for holding incoming information. It’s an active desktop where your brain processes information by making sense of new input and linking it with long-term memories. It also works in the opposite direction, by actively processing already stored information. Whether we hear eye-screem as “ice cream” or “I scream” will depend on how the context and our experience guide our interpreting and encoding the sounds. To emphasize the active processing that takes place in this middle stage, psychologists use the term working memory. Right now, you are using your working memory to link the information you’re reading with your previously stored information (Cowan, 2010; Kail & Hall, 2001).

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For most of you, what you are reading enters working memory through vision. You might also repeat the information using auditory rehearsal. As you integrate these memory inputs with your existing long-term memory, your attention is focused. In Baddeley’s (2002) model, a central executive handles this focused processing (FIGURE 22.4).

Without focused attention, information often fades. If you think you can look something up later, you attend to it less and forget it more quickly. In one experiment, people read and typed new bits of trivia they would later need, such as “An ostrich’s eye is bigger than its brain.” If they knew the information would be available online, they invested less energy and remembered it less well (Sparrow et al., 2011; Wegner & Ward, 2013). Sometimes Google replaces rehearsal.