As you begin this chapter on memory processes, please take a moment to call to mind your own earliest memory. How long ago did the memory originate? How vivid a scene do you recall? Has your memory been influenced by other people’s recollections of the same event? Now, a slightly different exercise. Please imagine what it would be like if you suddenly had no memory of your past—of the people you have known or of events that have happened to you. You wouldn’t remember your best friend’s face, or your 10th birthday, or your senior prom. Without such time anchors, how would you maintain a sense of who you are—of your self-identity? Or suppose you lost the ability to form any new memories. What would happen to your most recent experiences? Could you follow a conversation or untangle the plot of a TV show? Everything would vanish, as if events had never existed, as if you had never had any thoughts in mind. If you have never given much thought to your memory, it’s probably because it tends to do its job reasonably well—you take it for granted, alongside other bodily processes, like digestion or breathing. But as with stomachaches or allergies, the times you notice your memory are likely to be the times when something goes wrong: You forget your car keys, an important date, lines in a play, or the answer to an examination question that you know you “really know.” There’s no reason you shouldn’t find these occasions irritating, but you should also reflect for a moment on the estimate that the average human brain can store 100 trillion bits of information. The task of managing such a vast array of information is a formidable one. Perhaps you shouldn’t be too surprised when an answer is sometimes not available when you need it! The goal for this chapter is to explain how you usually remember so much and why you forget some of what you have known. We will explore how you get your everyday experiences into and out of memory. You will learn what psychology has discovered about different types of memories and about how those memories work. In the course of learning the many facts of memory, you’re likely to gain an appreciation for how wonderful memory is. One last thing: Because this is a chapter on memory, let’s put your memory immediately to work. Please try to remember the number 51. Do whatever you need to do to remember 51. And yes, there will be a test! WHAT IS MEMORY? Memory is the capacity to encode, store, and retrieve information. In this chapter, we will consider memory to be a type of information processing. The bulk of our attention, therefore, will be trained on the flow of information in and out of your memory systems. Our examination of the processes that guide the acquisition and retrieval of information will enable you to refine your sense of what memory means. memory the mental capacity to encode, store, and retrieve information. Functions of Memory When you think about memory, what is most likely to come to mind at first are situations in which you use your memory to recall (or try to recall) specific events or information: your favorite movie, the dates of World War II, or your student ID number. In fact, one of the important functions of memory is to allow you to have conscious access to the personal and collective past. But memory does much more for you than that. It also enables you to have effortless continuity of experience from one day to the next. When you walk through your neighborhood, for example, it is this second function of memory that makes the buildings along the way seem familiar. In defining types of memories, I will make plain to you how hard your memory works to fulfill these functions, often outside of conscious awareness. How are actors and actresses able to remember all the different aspects—movements, expressions, and words—of their performances? Implicit and Explicit Memory Consider Figure 7.1. What’s wrong with this picture? It probably strikes you as unusual that there’s a rabbit in the kitchen. But where does this feeling come from? You probably didn’t go through the objects in the picture one by one and ask yourself, “Does the toaster belong?” “Do the cabinets belong?” Rather, the image of the rabbit jumps out at you as being out of place. This simple example allows you to understand the difference between explicit and implicit uses of memory. For circumstances in which you engage conscious effort to encode or retrieve information, those are explicit uses of memory. When you encode or retrieve information without conscious effort, those are implicit uses of memory. Your discovery of the rabbit is implicit because your memory processes brought past knowledge of kitchens to bear on your interpretation of the picture without any particular effort on your part. Suppose now I asked you, “What’s missing from the picture?” To answer this second question, you probably have to put explicit memory to work. What appears in the typical kitchen? What’s missing? (Did you think of the sink or the stove?) Thus, when it comes to using knowledge stored in memory, sometimes the use will be implicit—the information becomes available without any conscious effort—and sometimes it will be explicit—you make a conscious effort to recover the information. explicit use of memory conscious effort to encode or recover information through memory processes. implicit uses of memory availability of information through memory processes without conscious effort to encode or recover information. FIGURE 7.1 What’s Wrong with This Picture? Did you think right away, “What’s a rabbit doing in the kitchen?” If the image of the rabbit immediately jumped out at you, it is because your memory processes performed an analysis of the scene outside of consciousness and delivered the rabbit as the odd element. The same distinction applies when it comes to the initial acquisition of memories. How do you know what should appear in a kitchen? Did you ever memorize a list of what appears there and what the appropriate configuration should be? Probably not. Rather, it’s likely that you acquired most of this knowledge without conscious effort. By contrast, you probably learned the names of many of the objects in the room explicitly. As you’ll see in Chapter 10, to learn the association between words and experiences, your younger self needed to engage in explicit memory processes. You learned the word refrigerator because someone called your explicit attention to the name of that object. The distinction between implicit and explicit memory greatly expands the range of questions researchers must address about memory processes (Roediger, 2008). Most early memory research focused on the explicit acquisition of information. Experimenters most frequently provided participants with new information to retain, and theories of memory were directed to explaining what participants could and could not remember under those circumstances. However, as you will see in this chapter, researchers have now devised methods for studying implicit memory as well. Thus you can obtain a more complete account of the variety of uses to which you put your memory. In fact, most circumstances in which you encode or retrieve information represent a mix of implicit and explicit uses of memory. Let’s turn now to a second dimension along which memories are distributed. Declarative and Procedural Memory Can you whistle? Go ahead and try. Or if you can’t whistle, try snapping your fingers. What kind of memory allows you to do these sorts of things? You probably remember having to learn these skills, but now they seem effortless. The earlier examples of implicit and explicit memories all involved the recollection of facts and events, which is called declarative memory. Now we see that you also have memories for how to do things, which is called procedural memory. Because the bulk of this chapter will be focused on how you acquire and use facts, let’s take a moment now to consider how you acquire the ability to do things. declarative memory Memory for information such as facts and events. procedural memory Memory for how things get done; the way perceptual, cognitive, and motor skills are acquired, retained, and used. Procedural memory refers to the way you remember how things get done. With enough practice, you are able to acquire, retain, and employ procedural memories for perceptual, cognitive, and motor skills. Theories of procedural memory often concern themselves with how much practice you need and over what period of time: How do you go from a conscious list of declarative facts about some activity to unconscious, automatic performance of that same activity (Taatgen et al., 2008)? And why is it that after learning a skill, you often find it difficult to go back and talk about the component declarative facts? We can see these phenomena at work in even the very simple activity of punching in a phone number that, over time, has become highly familiar. At first, you probably had to think your way through each digit, one at a time. You had to work through a list of declarative facts: Why does pretending to punch in a number help you to remember it? First, I must punch 2, Next, I must punch 0, Then I punch 7, and so on. However, when you began to punch in the number often enough, you could start to produce it as one unit—a swift sequence of actions on the touch-tone pad. The process at work is called production compilation: The mental commands that produce separate actions get compiled together (Taatgen & Lee, 2003). As a consequence of practice, you are able to carry out longer sequences of the activity without conscious intervention and mental effort (Stocco et al., 2010). But you also don’t have conscious access to the content of these compiled units: Back at the telephone, it’s not uncommon to find someone who can’t actually remember the phone number without pretending to punch it in. In general, production compilation makes it hard to share your procedural knowledge with others. You may have noticed this if your parents tried to teach you to drive. Although they may be good drivers themselves, they may not have been very good at communicating the content of compiled good-driving procedures. You may also have noticed that production compilation can lead to errors. If you are a skilled typist, you’ve probably suffered from the the problem: As soon as you hit the t and the h keys, your finger may fly to the e, even if you’re really trying to type throne or thistle. Once you have sufficiently committed the execution of the to procedural memory, you can do little else but finish the sequence. Without procedural memory, life would be extremely laborious—you would be doomed to go step by step through every activity. However, each time you mistakenly type the, you can reflect on the trade-off between efficiency and potential error. Let’s continue now to an overview of the basic processes that apply to all these different types of memory. An Overview of Memory Processes No matter what the category of memory, being able to use knowledge at some later time requires the operation of three mental processes: encoding, storage, and retrieval. Encoding is the initial processing of information that leads to a representation in memory. Storage is the retention over time of encoded material. Retrieval is the recovery at a later time of the stored information. Simply put, encoding gets information in, storage holds it until you need it, and retrieval gets it out. Let’s now expand on these ideas. encoding The process by which a mental representation is formed in memory. storage The retention of encoded material over time. retrieval The recovery of stored information from memory. Encoding requires that you form mental representations of information from the external world. You can understand the idea of mental representations by analogy to representations outside your head. Imagine I wanted to know something about the best gift you got at your last birthday party. (Let’s suppose it’s not something you have with you.) What could you do to inform me about the gift? You might describe the properties of the object. Or you might draw a picture. Or you might pretend that you’re using the object. In each case, these are representations of the original object. Although none of the representations is likely to be quite as good as having the real thing present, they should allow me to acquire knowledge of the most important aspects of the gift. Mental representations work much the same way. They preserve important features of past experiences in a way that enables you to re-present those experiences to yourself. If information is properly encoded, it will be retained in storage over some period of time. Storage requires both short-and long-term changes in the structures of your brain. At the end of the chapter, we will see how researchers are attempting to locate the brain structures that are responsible for storing new and old memories. We will also see what happens in cases of extreme amnesia, where individuals become incapable of storing new memories. Retrieval is the payoff for all your earlier effort. When it works, it enables you to gain access—often in a split second—to information you stored earlier. Can you remember what comes before storage: decoding or encoding? The answer is simple to retrieve now, but will you still be able to retrieve the answer as swiftly and confidently when you are tested on this chapter’s contents days or weeks from now? Discovering how you are able to retrieve one specific bit of information from the vast quantity of information in your memory storehouse is a challenge facing psychologists who want to know how memory works. Although it is easy to define encoding, storage, and retrieval as separate memory processes, the interaction among