CH 5 PDF Psychology PDF

SOME QUESTIONS WE WILL CONSIDER ◗ Why can we remember a telephone number long enough to place a call, but then we forget it almost immediately? (138) ◗ How is memory involved in processes such as doing a math problem? (143) ◗ Do we use the same memory system to remember things we have seen and thing...

SOME QUESTIONS WE WILL CONSIDER ◗ Why can we remember a telephone number long enough to place a call, but then we forget it almost immediately? (138) ◗ How is memory involved in processes such as doing a math problem? (143) ◗ Do we use the same memory system to remember things we have seen and things we have heard? (145) S o much has been written about memory—the advantages of having a good memory, the pitfalls of forgetting, or in the worst case, losing one’s ability to remember—that it may hardly seem necessary to read a cognitive psychology textbook to understand what memory is. But as you will see over the next four chapters, “memory” is not just one thing. Memory, like attention, comes in many forms. One of the purposes of this chapter and the next is to introduce the different types of memory, describing the properties of each type and the mechanisms responsible for them. Let’s begin with two definitions of memory: Memory is the process involved in retaining, retrieving, and using information about stimuli, images, events, ideas, and skills after the original information is no longer present. ➤ Memory is active any time some past experience has an effect on the way you think or behave now or in the future ( Joordens, 2011). ➤ From these definitions, it is clear that memory has to do with the past affecting the present, and possibly the future. But while these definitions are correct, we need to consider the various ways in which the past can affect the present to really understand what memory is. When we do this, we will see that there are many different kinds of memory. With apologies to the English poet Elizabeth Barrett Browning, whose famous poem to her husband begins “How do I love thee, let me count the ways,” let’s consider a woman we’ll call Christine as she describes incidents from her life that illustrate a related question: “How do I remember thee, let me count the ways” (see Figure 5.1). My first memory of you was brief and dramatic. It was the Fourth of July, and everyone was looking up at the sky to see the fireworks. But what I saw was your face—illuminated ➤ Figure 5.1 Five types of memory described by Christine. See text for details. Chapter 5 Chapters 6, 7, 8 Short-term Long-term episodic Picnic Long-term procedural Sensory Flash How to ride bike Long-term semantic 130 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 130 4/19/18 6:56 PM Short-Term and Working Memory 131 for just a moment by a flash, and then there was darkness. But even in the darkness I held your image in my mind for a moment. When something is presented briefly, such as a face illuminated by a flash, your perception continues for a fraction of a second in the dark. This brief persistence of the image, which is one of the things that makes it possible to perceive movies, is called sensory memory. Luckily, I had the presence of mind to “accidentally” meet you later so we could exchange phone numbers. Unfortunately, I didn’t have my cell phone with me or anything to write with, so I had to keep repeating your number over and over until I could write it down. Information that stays in our memory for brief periods, about 10 to 15 seconds if we don’t repeat it over and over as Christine did, is short-term memory or working memory. And the rest is history, because I have countless memories of all the things we have done. I especially remember that crisp fall day when we went bike riding to that place in the woods where we had a picnic. Long-term memory is responsible for storing information for long periods of time— which can extend from minutes to a lifetime. Long-term memories of experiences from the past, like the picnic, are episodic memories. The ability to ride a bicycle, or do any of the other things that involve muscle coordination, is a type of long-term memory called procedural memory. I must admit, however, that as much as I remember many of the things we have done, I have a hard time remembering the address of the first apartment we lived in, although, luckily for me, I do remember your birthday. Another type of long-term memory is semantic memory—memories of facts such as an address or a birthday or the names of different objects (“that’s a bicycle”). We will describe sensory memory and short-term memory in this chapter, we will compare short-term and long-term memory at the beginning of Chapter 6, and then spend the rest of Chapter 6 plus Chapters 7 and 8 on long-term memory. We will see that although people often mistakenly use the term “short-term memory” to refer to memory for events that happened minutes, hours, or even days ago, it is actually much briefer. In Chapter 6 we will note that this misconception about the length of short-term memory is reflected in how memory loss is described in movies. People also often underestimate the importance of short-term memory. When I ask my students to create a “top 10” list of what they use memory for, most of the items come under the heading of long-term memory. The four top items on their list are the following: Material for exams Their daily schedule Names Directions to places Your list may be different, but items from short-term memory rarely make the list, especially since the Internet and cell phones make it less necessary to repeat phone numbers over and over to keep them alive in memory. So what is the purpose of sensory and short-term memory? Sensory memory is important when we go to the movies (more on that soon), but the main reason for discussing sensory memory is to demonstrate an ingenious procedure for measuring how much information we can take in immediately, and how much of that information remains half a second later. The purpose of short-term memory will become clearer as we describe its characteristics, but stop for a moment and answer this question: What are you aware of right now? Some Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 131 4/18/18 4:00 PM 132 CHAPTER 5 Short-Term and Working Memory material you are reading about memory? Your surroundings? Noise in the background? Whatever your answer, you are describing what is in short-term memory. Everything you know or think about at each moment in time is in short-term memory. Thirty seconds from now your “old” short-term memories may have faded, but new ones will have taken over. Your “to do” list in long-term memory may be important, but as you are doing each of the things on your list, you are constantly using your short-term memory. As you will see in this chapter, short-term memory may be short in duration, but it looms large in importance. We begin our description of sensory and short-term memory by describing an early and influential model of memory called the modal model, which places sensory and short-term memory at the beginning of the process of memory. The Modal Model of Memory Input Sensory memory Shortterm memory Remember Donald Broadbent’s (1958) filter model of attention, which introduced the flow chart that helped usher in the information processing approach to cognition (Chapter 1, page 14; Chapter 4, page 95). Ten years after Broadbent introduced his flow diagram for attention, Richard Atkinson and Richard Shiffrin (1968) introduced Rehearsal: A control process the flow diagram for memory shown in Figure 5.2, which is called the modal model of memory. This model proposed Longthree types of memory: term memory Output ➤ Figure 5.2 Flow diagram for Atkinson and Shiffrin’s (1968) modal model of memory. This model, which is described in the text, is called the modal model because it contains features of many of the memory models that were being proposed in the 1960s. 1. Sensory memory is an initial stage that holds all incoming information for seconds or fractions of a second. 2. Short-term memory (STM) holds five to seven items for about 15 to 20 seconds. We will describe the characteristics of short-term memory in this chapter. 3. Long-term memory (LTM) can hold a large amount of information for years or even decades. We will describe long-term memory in Chapters 6, 7, and 8. The types of memory listed above, each of which is indicated by a box in the model, are called the structural features of the model. As we will see, the short-term memory and long-term memory boxes in this diagram were expanded by later researchers, who modified the model to distinguish between the different types of short- and long-term memories. But for now, we take this simpler modal model as our starting point because it illustrates important principles about how different types of memory operate and interact. Atkinson and Shiffrin also proposed control processes, which are dynamic processes associated with the structural features that can be controlled by the person and may differ from one task to another. An example of a control process that operates on short-term memory is rehearsal—repeating a stimulus over and over, as you might repeat a telephone number in order to hold it in your mind after looking it up on the Internet. Rehearsal is symbolized by the blue arrow in Figure 5.2. Other examples of control processes are (1) strategies you might use to help make a stimulus more memorable, such as relating the digits in a phone number to a familiar date in history, and (2) strategies of attention that help you focus on information that is particularly important or interesting. To illustrate how the structural features and control processes operate, let’s consider what happens as Rachel looks up the number for Mineo’s Pizza on the Internet (Figure 5.3). When she first looks at the screen, all of the information that enters her eyes is registered in sensory memory (Figure 5.3a). Rachel uses the control process of selective attention to focus on the number for Mineo’s, so the number enters her short-term memory (Figure 5.3b), and she uses the control process of rehearsal to keep it there (Figure 5.3c). Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 132 4/18/18 4:00 PM The Modal Model of Memory All info on screen enters sensory memory. Sensory STM LTM Sensory STM LTM 133 (a) Focus on 555-5100. It enters STM. (b) 555-5100 555-5100 555-5100 Rehearsing Rehearsal Rehearse the number to keep it in STM while making the phone call. Sensory STM LTM Remember number to make call (c) Memorizing Storage Store number in LTM. Sensory STM LTM (d) 555-5100 Retrieval (e) Retrieve number from LTM. It goes back to STM and is remembered. Awareness Sensory STM Remember number to make call again LTM Retrieval ➤ Figure 5.3 What happens in different parts of Rachel’s memory as she is (a, b) looking up the phone number, (c) calling the pizza shop, and (d) memorizing the number. A few days later, (e) she retrieves the number from long-term memory to order pizza again. The parts of the modal model that are outlined in red indicate which processes are activated for each action that Rachel takes. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 133 4/18/18 4:00 PM 134 CHAPTER 5 Short-Term and Working Memory Rachel knows she will want to use the number again later, so she decides that in addition to storing the number in her cell phone, she is going to memorize the number so it will also be stored in her mind. The process she uses to memorize the number, which involves control processes that we will discuss in Chapter 6, transfers the number into long-term memory, where it is stored (Figure 5.3d). The process of storing the number in long-term memory is called encoding. A few days later, when Rachel’s urge for pizza returns, she remembers the number. This process of remembering information that is stored in long-term memory is called retrieval (Figure 5.3e). One thing that becomes apparent from our example is that the components of memory do not act in isolation. Thus, the phone number is first stored in Rachel’s STM, but because information is easily lost from STM (as when you forget a phone number), Rachel transfers the phone number into LTM (green arrow), where it is held until she needs it later. When she then remembers the phone number later, it is returned to STM (black arrow), and Rachel becomes aware of the phone number. We will now consider each component of the model, beginning with sensory memory. Sensory Memory Sensory memory is the retention, for brief periods of time, of the effects of sensory stimulation. We can demonstrate this brief retention for the effects of visual stimulation with two familiar examples: the trail left by a moving sparkler and the experience of seeing a film. The Sparkler’s Trail and the Projector’s Shutter It is dark out on the Fourth of July, and you put a match to the tip of a sparkler. As sparks begin radiating from the tip, you sweep the sparkler through the air, creating a trail of light (Figure 5.4a). Although it appears that this trail is created by light left by the sparkler as you wave it through the air, there is, in fact, no light along this trail. The lighted trail is a creation of your mind, which retains a perception of the sparkler’s light for a fraction of a second (Figure 5.4b). This retention of the perception of light in your mind is called the persistence of vision. Persistence of vision is the continued perception of a visual stimulus even after it is no longer present. This persistence lasts for only a fraction of a second, so it isn’t obvious in everyday experience when objects are present for long periods. However, the persistence of vision effect is noticeable for brief stimuli, like the moving sparkler or rapidly flashed pictures in a movie theater. While you are watching a movie, you may see actions moving smoothly across the screen, but what is actually projected is quite different. First, a single film frame is positioned in front of the projector lens, and when the projector’s shutter opens and closes, the image on the film frame flashes onto the screen. When the shutter is closed, the film moves on to the next frame, and during that time the screen is dark. When the next frame has arrived in front of the lens, the shutter opens and closes again, flashing the next image onto the screen. This process is repeated rapidly, 24 times per second, with 24 still images flashed on the screen every second and each image followed by a brief period of darkness (see Table 5.1). (Note that some filmmakers are now beginning to experiment with higher frame rates, as in Peter Jackson’s The Hobbit: An Unexpected Journey (2012), shot at 48 frames per second, and Ang Lee’s Billy Lynn’s Long Halftime Walk (2016), shot at 120 frames per second.) A person viewing the film doesn’t see the dark intervals between the images because the persistence of vision fills in the darkness by retaining the image of the previous frame. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 134 4/18/18 4:00 PM Sensory Memory 135 Perceptual trail Gordon Langsbury/Alamy Stock Photo ➤ Figure 5.4 (a) A sparkler can cause a trail of light when it is moved rapidly. (b) This trail occurs because the perception of the light is briefly held in the mind. TABLE 5.1 Persistence of Vision in Film* What Happens? What Is on the Screen? What Do You Perceive? Film frame 1 is projected. Picture 1 Picture 1 Shutter closes and film moves to the next frame. Darkness Picture 1 (persistence of vision) Shutter opens and film frame 2 is projected. Picture 2 Picture 2 *The sequence indicated here is for movies projected using traditional film. Newer digital movie technologies are based on information stored on discs. Sperling’s Experiment: Measuring the Capacity and Duration of the Sensory Store The persistence of vision effect that adds a trail to our perception of moving sparklers and fills in the dark spaces between frames in a film has been known since the early days of psychology (Boring, 1942). But George Sperling (1960) wondered how much information people can take in from briefly presented stimuli. He determined this in a famous experiment in which he flashed an array of letters, like the one in Figure 5.5a, on the screen for 50 milliseconds (50/1000 second) and asked his participants to report as many of the letters as possible. This part of the experiment used the whole report method; that is, participants were asked to report as many letters as possible from the entire 12-letter display. Given this task, they were able to report an average of 4.5 out of the 12 letters. At this point, Sperling could have concluded that because the exposure was brief, participants saw only an average of 4.5 of the 12 letters. However, some of the participants in Sperling’s experiment reported that they had seen all the letters, but that their perception had faded rapidly as they were reporting the letters, so by the time they had reported 4 or 5 letters, they could no longer see or remember the other letters. Sperling reasoned that if participants couldn’t report the 12-letter display because of fading, perhaps they would do better if they were told to just report the letters in a single 4-letter row. Sperling devised the partial report method to test this idea. Participants saw Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 135 4/18/18 4:00 PM 136 CHAPTER 5 Short-Term and Working Memory the 12-letter display for 50 ms, as before, but immediately after it was flashed, they heard a tone that told them which row of the matrix to report. A high-pitched tone indicated the top row; a medium-pitch indicated the middle row; and a low-pitch indicated the bottom row (Figure 5.5b). Because the tones were presented immediately after the letters were turned off, the participant’s attention was directed not to the actual letters, which were no longer present, but to whatever trace remained in the participant’s mind after the letters were turned off. When the participants focused their attention on one of the rows, they correctly reported an average of about 3.3 of the 4 letters (82 percent) in that row. Because this occurred no matter which row they were reporting, Sperling concluded that immediately after the 12-letter display was presented, participants saw an average of 82 percent of all of the letters but were not able to report all of these letters because they rapidly faded as the initial letters were being reported. Sperling then did an additional experiment to determine the time course of this fading. For this experiment, Sperling devised a delayed partial report method in which the letters were flashed on and off and then the cue tone was presented after a short delay (Figure 5.5c). The result of the delayed partial report experiments was that when the cue ➤ Figure 5.5 Procedure for three of Sperling’s (1960) experiments. (a) Whole report method: Person saw all 12 letters at once for 50 ms and reported as many as he or she could remember. (b) Partial report: Person saw all 12 letters, as before, but immediately after they were turned off, a tone indicated which row the person was to report. (c) Delayed partial report: Same as (b), but with a short delay between extinguishing the letters and presentation of the tone. X F D Z C X M L T A F N B C D Z P Result: average of 4.5 letters reported out of 12 (a) Whole report M X X M L T A F N B C D Z P L High Medium Low Immediate tone (b) Partial report Tone immediate Result: average of 3.3 letters reported out of 4 X M L T A F N B C D Z P Medium Low Delay (c) Partial report Tone delayed B High Delayed tone Result: average of 1 letter reported out of 4, after 1-sec delay Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 136 4/18/18 4:00 PM Short-Term Memory : Storage 137 Percentage of letters available to participant 100 75 Partial report Whole report 50 25 0 0 0.2 0.4 0.6 0.8 Delay of tone (sec) 1.0 ➤ Figure 5.6 Results of Sperling’s (1960) partial report experiments. The decrease in performance is due to the rapid decay of iconic memory (sensory memory in the modal model). tones were delayed for 1 second after the flash, participants were able to report only slightly more than 1 letter in a row. Figure 5.6 plots this result, showing the percentage of letters available to the participants from the entire display as a function of time following presentation of the display. This graph indicates that immediately after a stimulus is presented, all or most of the stimulus is available for perception. This is sensory memory. Then, over the next second, sensory memory fades. Sperling concluded from these results that a short-lived sensory memory registers all or most of the information that hits our visual receptors, but that this information decays within less than a second. This brief sensory memory for visual stimuli, called iconic memory or the visual icon (icon means “image”), corresponds to the sensory memory stage of Atkinson and Shiffrin’s modal model. Other research using auditory stimuli has shown that sounds also persist in the mind. This persistence of sound, called echoic memory, lasts for a few seconds after presentation of the original stimulus (Darwin et al., 1972). An example of echoic memory is when you hear someone say something, but you don’t understand at first and say “What?” But even before the person can repeat what was said, you “hear” it in your mind. If that has happened to you, you’ve experienced echoic memory. In the next section, we consider the second stage of the modal model, short-term memory, which also holds information briefly, but for much longer than sensory memory. Short-Term Memory: Storage We saw in the preceding section that although sensory memory fades rapidly, Sperling’s participants could report some of the letters. These letters are the part of the stimuli that has moved on to short-term memory in the flow diagram in Figure 5.2. Short-term memory (STM) is the system involved in storing small amounts of information for a brief period of time (Baddeley et al., 2009). Thus, whatever you are thinking about right now, or remember from what you have just read, is in your short-term memory. As we will see below, most of this information is eventually lost, and only some of it reaches the more permanent store of long-term memory (LTM). Because of the brief duration of STM, it is easy to downplay its importance compared to LTM, but, as we will see, STM is responsible for a great deal of our mental life. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 137 4/18/18 4:00 PM 138 CHAPTER 5 Short-Term and Working Memory Everything we think about or know at a particular moment in time involves STM because short-term memory is our window on the present. (Remember from Figure 5.3e that Rachel became aware of the pizzeria’s phone number by transferring it from LTM, where it was stored, back into her STM.) We will now describe some early research on STM that focused on answering the following two questions: (1) What is the duration of STM? (2) What is the capacity of STM? These questions were answered in experiments that used the method of recall to test memory. METHOD Recall Most of the experiments we will be describing in this chapter involve recall, in which participants are presented with stimuli and then, after a delay, are asked to report back as many of the stimuli as possible. Memory performance can be measured as a percentage of the stimuli that are remembered. (For example, studying a list of 10 words and later recalling 3 of them is 30 percent recall.) Participants’ responses can also be analyzed to determine whether there is a pattern to the way items are recalled. (For example, if participants are given a list consisting of types of fruits and models of cars, their recall can be analyzed to determine whether they grouped cars together and fruits together as they were recalling them.) Recall is also involved when a person is asked to recollect life events, such as graduating from high school, or to recall facts they have learned, such as the capital of Nebraska. What Is the Duration of Short-Term Memory? One of the major misconceptions about short-term memory is that it lasts for a relatively long time. It is not uncommon for people to refer to events they remember from a few days or weeks ago as being remembered from short-term memory. However, short-term memory, as conceived by cognitive psychologists, lasts 15 to 20 seconds or less. This was demonstrated by John Brown (1958) in England and Lloyd Peterson and Margaret Peterson (1959) in the United States, who used the method of recall to determine the duration of STM. Peterson and Peterson presented participants with three letters, such as FZL or BHM, followed by a number, such as 403. Participants were instructed to begin counting backwards by threes from that number. This was done to keep participants from rehearsing the letters. After intervals ranging from 3 to 18 seconds, participants were asked to recall the three letters. Participants correctly recalled about 80 percent of the three letter groups when they had counted for only 3 seconds, but recalled only about 12 percent of the groups after counting for 18 seconds. Results such as this have led to the conclusion that the effective duration of STM (when rehearsal is prevented, as occurred when counting backwards) is about 15 to 20 seconds or less (Zhang & Luck, 2009). How Many Items Can Be Held in Short-Term Memory? Not only is information lost rapidly from STM, but there is a limit to how much information can be held there. As we will see, estimates for how many items can be held in STM range from four to nine. Digit Span One measure of the capacity of STM is provided by the digit span—the number of digits a person can remember. You can determine your digit span by doing the following demonstration. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 138 4/18/18 4:00 PM Short-Term Memory : Storage D E M O N S T R AT I O N 139 Digit Span Using an index card or piece of paper, cover all of the numbers below. Move the card down to uncover the first string of numbers. Read the first set of numbers once, cover it up, and then write the numbers down in the correct order. Then move the card to the next string, and repeat this procedure until you begin making errors. The longest string you are able to reproduce without error is your digit span. 2149 39678 649784 7382015 84264132 482392807 5852984637 If you succeeded in remembering the longest string of digits, you have a digit span of 10 or perhaps more. According to measurements of digit span, the average capacity of STM is about five to nine items—about the length of a phone number. This idea that the limit of STM is somewhere between five and nine was suggested by George Miller (1956), who summarized the evidence for this limit in his paper “The Magical Number Seven, Plus or Minus Two,” described in Chapter 1 (page 15). Change Detection More recent measures of STM capacity have set the limit at about four items (Cowan, 2001). This conclusion is based on the results of experiments like one by Steven Luck and Edward Vogel (1997), which measured the capacity of STM by using a procedure called change detection. METHOD Change Detection Following the “Change Detection” demonstration on page 117, we described experiments in which two pictures of a scene were flashed one after the other and the participants’ task was to determine what had changed between the first and second pictures. The conclusion from these experiments was that people often miss changes in a scene. Change detection has also been used with simpler stimuli to determine how much information a person can retain from a briefly flashed stimulus. An example of change detection is shown in Figure 5.7, which shows stimuli like the ones used in Luck and Vogel’s experiment. The display on the left was flashed for 100 ms, followed by 900 ms of darkness and then the new display on the right. The participant’s task was to indicate whether the second display was the same as or different from the first. (Notice that the color of one of the squares is changed in the second display.) This task is easy if the number of items is within the capacity of STM (Figure 5.7a) but becomes harder when the number of items becomes greater than the capacity of STM (Figure 5.7b). Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 139 4/18/18 4:00 PM 140 CHAPTER 5 Short-Term and Working Memory 100 ms 900 ms delay (a) 2,000 ms Same or different? Percent correct 100 75 50 100 ms (b) 900 ms delay 2,000 ms Same or different? ➤ Figure 5.7 (a) Stimuli used by Luck and Vogel (1997). The participant sees the first display and then indicates whether the second display is the same or different. In this example, the color of one square is changed in the second display. (b) Luck and Vogel stimuli showing a larger number of items. 0 4 8 12 Number of squares ➤ Figure 5.8 Result of Luck and Vogel’s (1997) experiment, showing that performance began to decrease once there were four squares in the display. (Source: Adapted from E. K. Vogel, A. W. McCollough, & M. G. Machizawa, Neural measures reveal individual differences in controlling access to working memory, Nature, 438, 500–503, 2005.) (Source: Adapted from E. K. Vogel, A. W. McCollough, & M. G. Machizawa, Neural measures reveal individual differences in controlling access to working memory, Nature, 438, 500–503, 2005.) The result of Luck and Vogel’s experiment, shown in Figure 5.8, indicates that performance was almost perfect when there were one to three squares in the arrays, but that performance began decreasing when there were four or more squares. Luck and Vogel concluded from this result that participants were able to retain about four items in their shortterm memory. Other experiments, using verbal materials, have come to the same conclusion (Cowan, 2001). These estimates of either four or five times to nine items set rather low limits on the capacity of STM. If our ability to hold items in memory is so limited, how is it possible to hold many more items in memory in some situations, as when words are arranged in a sentence? The answer to this question was proposed by George Miller, who introduced the idea of chunking in his “Seven, Plus or Minus Two” paper. Chunking Miller (1956) introduced the concept of chunking to describe the fact that small units (like words) can be combined into larger meaningful units, like phrases, or even larger units, like sentences, paragraphs, or stories. Consider, for example, trying to remember the following words: monkey, child, wildly, zoo, jumped, city, ringtail, young. How many units are there in this list? There are eight words, but if we group them differently, they can form the following four pairs: ringtail monkey, jumped wildly, young child, city zoo. We can take this one step further by arranging these groups of words into one sentence: The ringtail monkey jumped wildly for the young child at the city zoo. A chunk has been defined as a collection of elements that are strongly associated with one another but are weakly associated with elements in other chunks (Cowan, 2001; Gobet et al., 2001). In our example, the word ringtail is strongly associated with the word monkey but is not as strongly associated with the other words, such as child or city. Thus, chunking in terms of meaning increases our ability to hold information in STM. We can recall a sequence of 5 to 8 unrelated words, but arranging the words to form a meaningful sentence so that the words become more strongly associated with one another increases the memory span to 20 words or more (Butterworth et al., 1990). Chunking of a series of letters is illustrated by the following demonstration. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 140 4/18/18 4:01 PM Short-Term Memory : Storage D E M O N S T R AT I O N 141 Remembering Letters Read the string of letters below at a rate of about one letter every second; then cover the letters and write down as many as you can, in the correct order. BCIFCNCASIBB How did you do? This task isn’t easy, because it involves remembering a series of 12 individual letters, which is larger than the usual letter span of 5 to 9. Now try remembering the following sequence of letters in order: CIAFBINBCCBS How did your performance on this list compare to the one above? Although the second list has the same letters as the first group, it was easier to remember if you realized that this sequence consists of the names of four familiar organizations. You can therefore create four chunks, each of which is meaningful, and therefore easy to remember. K. Anders Ericsson and coworkers (1980) demonstrated an effect of chunking by showing how a college student with average memory ability was able to achieve amazing feats of memory. Their participant, S.F., was asked to repeat strings of random digits that were read to him. Although S.F. had a typical memory span of 7 digits, after extensive training (230 one-hour sessions), he was able to repeat sequences of up to 79 digits without error. How did he do it? S.F. used chunking to recode the digits into larger units that formed meaningful sequences. S.F. was a runner, so some of the sequences were running times. For example, 3,492 became “3 minutes and 49 point 2 seconds, near world-record mile time.” He also used other ways to create meaning, so 893 became “89 point 3, very old man.” This example illustrates an interaction between STM and LTM, because S.F created some of his chunks based on his knowledge of running times that were stored in LTM. Chunking enables the limited-capacity STM system to deal with the large amount of information involved in many of the tasks we perform every day, such as chunking letters into words as you read this, remembering the first three numbers of familiar telephone exchanges as a unit, and transforming long conversations into smaller units of meaning. How Much Information Can Be Held in Short-Term Memory? The idea that the capacity of short-term memory can be specified as a number of items, as described in the previous section, has generated a great deal of research. But some researchers have suggested that rather than describing memory capacity in terms of “number of items,” it should be described in terms of “amount of information.” When referring to visual objects, information has been defined as visual features or details of the object that are stored in memory (Alvarez & Cavanagh, 2004). We can understand the reasoning behind the idea that information is important by considering storing pictures on a computer flash drive. The number of pictures that can be stored depends on the size of the drive and on the size of the pictures. Fewer large pictures, which have files that contain more detail, can be stored because they take up more space in memory. With this idea in mind, George Alvarez and Patrick Cavanagh (2004) did an experiment using Luck and Vogel’s change detection procedure. But in addition to colored squares, they also used more complex objects like the ones in Figure 5.9a. For example, for the shaded cubes, which were the most complex stimuli, a participant would see a display containing a number of different cubes, followed by a blank interval, followed by a display Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 141 4/18/18 4:01 PM CHAPTER 5 Short-Term and Working Memory ➤ Figure 5.9 (a) Some of the stimuli used in Alvarez and Cavanagh’s (2004) change detection experiment. The stimuli range from low information (colored squares) to high information (cubes). In the actual experiments, there were six different objects in each set. (b) Results showing the average number of objects that could be remembered for each type of stimulus. (Source: Adapted from G. A. Alvarez & P. Cavanagh, The capacity of visual short-term memory is set both by visual information load and by number of objects, Psychological Science, 15, 106–111, 2004.) 5 Colored squares 4 Chinese characters Capacity 142 Random polygons 2 1 0 Shaded cubes (a) 3 (b) that was either the same as the first one or in which one of the cubes was different. The participant’s task was to indicate whether the two displays were the same or different. The result, shown in Figure 5.9b, was that participants’ ability to make the same/different judgment depended on the complexity of the stimuli. Memory capacity for the colored squares was 4.4, but capacity for the cubes was only 1.6. Based on this result, Alvarez and Cavanagh concluded that the greater the amount of information in an image, the fewer items that can be held in visual short-term memory. Should short-term memory capacity be measured in terms of “number of items” (Awh et al., 2007; Fukuda et al., 2010; Luck & Vogel, 1997) or “amount of detailed information” (Alvaraz & Cavanagh, 2004; Bays & Husain, 2008; Brady et al., 2011)? There are experiments that argue for both ideas, and the discussion among researchers is continuing. There is, however, agreement that whether considering items or information, there are limits on how much information we can store in short-term memory. Our discussion of STM up to this point has focused on two properties: how long information is held in STM and how much information can be held in STM. Considering STM in this way, we could compare it to a container like a leaky bucket that can hold a certain amount of water for a limited amount of time. But as research on STM progressed, it became apparent that the concept of STM as presented in the modal model was too narrow to explain many research findings. The problem was that STM was described mainly as a short-term storage mechanism. As we will see next, more goes on in short-term memory than storage. Information doesn’t just sit in STM; it can be manipulated in the service of mental processes such as computation, learning, and reasoning. T E ST YOUR SELF 5.1 1. The chapter began with Christine’s descriptions of five different types of memory. What are these? Which are of short duration? Of long duration? Why is shortterm memory important? 2. Describe Atkinson and Shiffrin’s modal model of memory both in terms of its structure (the boxes connected by arrows) and the control processes. Then describe how each part of the model comes into play when you decide you want to order pizza but can’t remember the pizzeria’s phone number. 3. Describe sensory memory and Sperling’s experiment in which he briefly flashed an array of letters to measure the capacity and duration of sensory memory. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 142 4/18/18 4:01 PM Working Memory : Manipulating Information 143 4. How did Peterson and Peterson measure the duration of STM? What is the approximate duration of STM? 5. What is the digit span? What does this indicate about the capacity of STM? 6. Describe Luck and Vogel’s change detection experiment. What is the capacity of STM according to the results of this experiment? 7. What is chunking? What does it explain? 8. What two proposals have been made about how the capacity of short-term memory should be measured? Describe Alvarez and Cavanagh’s experiment and their conclusion. Working Memory: Manipulating Information Working memory, which was introduced in a paper by Baddeley and Hitch (1974), is defined as “a limited-capacity system for temporary storage and manipulation of information for complex tasks such as comprehension, learning, and reasoning.” The italicized portion of this definition is what makes working memory different from the old modal model conception of short-term memory. Short-term memory is concerned mainly with storing information for a brief period of time (for example, remembering a phone number), whereas working memory is concerned with the manipulation of information that occurs during complex cognition (for example, remembering numbers while reading a paragraph). We can understand the idea that working memory is involved with the manipulation of information by considering a few examples. First, let’s listen in on a conversation Rachel is having with the pizza shop: Rachel: “I’d like to order a large pizza with broccoli and mushrooms.” Reply: “I’m sorry, but we’re out of mushrooms. Would you like to substitute spinach instead? Rachel was able to understand the pizza shop’s reply by holding the first sentence, “I’m sorry, but we’re out of mushrooms,” in her memory while listening to the second sentence, and then making the connection between the two. If she had remembered only “Would you like to substitute spinach instead?” she wouldn’t know whether it was being substituted for the broccoli or for the mushrooms. In this example, Rachel’s short-term memory is being used not only for storing information but also for active processes like understanding conversations. Another example of an active process occurs when we solve even simple math problems, such as “Multiply 43 times 6 in your head.” Stop for a moment and try this while being aware of what you are doing in your head. One way to solve this problem involves the following steps: Visualize: 43 3 6. Multiply 3 3 6 5 18. Hold 8 in memory, while carrying the 1 over to the 4. Multiply 6 3 4 5 24. Add the carried 1 to the 24. Place the result, 25, next to the 8. The answer is 258. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 143 4/18/18 4:01 PM 144 CHAPTER 5 Short-Term and Working Memory It is easy to see that this calculation involves both storage (holding the 8 in memory, remembering the 6 and 4 for the next multiplication step) and active processes (carrying the 1, multiplying 6 3 4) at the same time. If only storage were involved, the problem could not be solved. There are other ways to carry out this calculation, but whatever method you choose involves both holding information in memory and processing information. The fact that STM and the modal model do not consider dynamic processes that unfold over time is what led Baddeley and Hitch to propose that the name working memory, rather than short-term memory, be used for the short-term memory process. Current researchers often use both terms, short-term memory and working memory, when referring to the short-duration memory process, but the understanding is that the function of this process, whatever it is called, extends beyond just storage. Returning to Baddeley, one of the things he noticed was that under certain conditions it is possible to carry out two tasks simultaneously, as illustrated in the following demonstration. D E M O N S T R AT I O N Reading Text and Remembering Numbers Here are four numbers: 7, 1, 4, and 9. Remember them, then cover them and read the following passage while keeping the numbers in your mind. Baddeley reasoned that if STM had a limited storage capacity of about the length of a telephone number, filling up the storage capacity should make it difficult to do other tasks that depend on STM. But he found that participants could hold a short string of numbers in their memory while carrying out another task, such as reading or even solving a simple word problem. How are you doing with this task? What are the numbers? What is the gist of what you have just read? According to Atkinson and Shiffrin’s modal model, it should only be possible to perform one of these tasks, which should occupy the entire STM. But when Baddeley did experiments involving tasks similar to those in the previous demonstration, he found that participants were able to read Verbal and Visual and Central auditory spatial executive while simultaneously remembering numbers. information information What kind of model can take into account both (1) the dynamic processes involved in cognitions such as understanding language and doing math problems and (2) the fact that people can carry out two tasks simultaBaddeley’s working memory model neously? Baddeley concluded that working memory must be dynamic and must also consist of a number of components that can function separately. He proposed three components: the phonological loop, the visuospatial sketch pad, and the central executive (Figure 5.10). ➤ Figure 5.10 Diagram of the three main The phonological loop consists of two components: the phonological components of Baddeley and Hitch’s (1974; store, which has a limited capacity and holds information for only a few Baddeley, 2000) model of working memory: the phonological loop, the visuospatial sketch pad, seconds, and the articulatory rehearsal process, which is responsible for and the central executive. rehearsal that can keep items in the phonological store from decaying. The phonological loop holds verbal and auditory information. Thus, when you are trying to remember a telephone number or a person’s name, or to understand what your cognitive psychology professor is talking about, you are using your phonological loop. The visuospatial sketch pad holds visual and spatial information. When you form a picture in your mind or do tasks like solving a puzzle or finding your way around campus, you are using your visuospatial sketch pad. As you can see from the diagram, the phonological loop and the visuospatial sketch pad are attached to the central executive. The central executive is where the major work of working memory occurs. The central executive pulls information from long-term memory and coordinates the activity of the phonological loop and visuospatial sketch pad by focusing on specific parts of a task and Phonological loop Visuospatial sketch pad Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 144 4/18/18 4:01 PM Working Memory : Manipulating Information deciding how to divide attention between different tasks. The central executive is therefore the “traffic cop” of the working memory system. To understand this “traffic cop” function, imagine you are driving in a strange city, a friend in the passenger seat is reading you directions to a restaurant, and the car radio is broadcasting the news. Your phonological loop is taking in the verbal directions; your sketch pad is helping you visualize a map of the streets leading to the restaurant; and your central executive is coordinating and combining these two kinds of information (Figure 5.11). In addition, the central executive might be helping you ignore the messages from the radio so you can focus your attention on the directions. We will now describe a number of phenomena that illustrate how the phonological loop handles language, how the visuospatial sketch pad holds visual and spatial information, and how the central executive uses attention to coordinate between the two. The Phonological Loop We will describe three phenomena that support the idea of a system specialized for language: the phonological similarity effect, the word length effect, and articulatory suppression. 145 Central executive coordinates verbal and visual information Phonological loop Visuospatial sketch pad Go left at the second corner Central executive focuses attention on relevant message “Good morning from Talk Radio 93” ➤ Figure 5.11 Tasks processed by the phonological loop (hearing directions, listening to the radio) and the visuospatial sketch pad (visualizing the route) are being coordinated by the central executive. The central executive also helps the driver ignore the messages from the radio so attention can be focused on hearing the directions. Phonological Similarity Effect The phonological similarity effect is the confusion of letters or words that sound similar. In an early demonstration of this effect, R. Conrad (1964) flashed a series of target letters on a screen and instructed his participants to write down the letters in the order they were presented. He found that when participants made errors, they were most likely to misidentify the target letter as another letter that sounded like the target. For example, “F” was most often misidentified as “S” or “X,” two letters that sound similar to “F,” but was not as likely to be confused with letters like “E,” that looked like the target. Thus, even though the participants saw the letters, the mistakes they made were based on the letters’ sounds. This result fits with our common experience with telephone numbers. Even though our contact with them is often visual, we usually remember them by repeating their sound over and over rather than by visualizing what the numbers looked like on the computer screen (also see Wickelgren, 1965). In present-day terminology, Conrad’s result would be described as a demonstration of the phonological similarity effect, which occurs when words are processed in the phonological store part of the phonological loop. Word Length Effect The word length effect occurs when memory for lists of words is better for short words than for long words. Thus, the word length effect predicts that more words will be recalled from List 1 (below) than from List 2. List 1: beast, bronze, wife, golf, inn, limp, dirt, star List 2: alcohol, property, amplifier, officer, gallery, mosquito, orchestra, bricklayer Each list contains eight words, but according to the word length effect, the second list will be more difficult to remember because it takes more time to pronounce and rehearse longer words and to produce them during recall (Baddeley et al., 1984). (Note, however, that some researchers have proposed that the word length effect does not occur under some conditions; Jalbert et al., 2011; Lovatt et al., 2000, 2002.) Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 145 4/18/18 4:01 PM 146 CHAPTER 5 Short-Term and Working Memory In another study of memory for verbal material, Baddeley and coworkers (1975) found that people are able to remember the number of items that they can pronounce in about 1.5–2.0 seconds (also see Schweickert & Boruff, 1986). Try counting out loud, as fast as you can, for 2 seconds. According to Baddeley, the number of words you can say should be close to your digit span. Articulatory Suppression Another way that the operation of the phonological loop has been studied is by determining what happens when its operation is disrupted. This occurs when a person is prevented from rehearsing items to be remembered by repeating an irrelevant sound, such as “the, the, the . . .” (Baddeley, 2000; Baddeley et al., 1984; Murray, 1968). This repetition of an irrelevant sound results in a phenomenon called articulatory suppression, which reduces memory because speaking interferes with rehearsal. The following demonstration, which is based on an experiment by Baddeley and coworkers (1984), illustrates this effect of articulatory suppression. D E M O N S T R AT I O N Articulatory Suppression Task 1: Read the following list. Then turn away and recall as many words as you can. dishwasher, hummingbird, engineering, hospital, homelessness, reasoning Task 2: Read the following list while repeating “the, the, the . . .” out loud. Then turn away and recall as many words as you can. automobile, apartment, basketball, mathematics, gymnasium, Catholicism Articulatory suppression makes it more difficult to remember the second list because repeating “the, the, the . . .” overloads the phonological loop, which is responsible for holding verbal and auditory information. Baddeley and coworkers (1984) found that repeating “the, the, the . . .” not only reduces the ability to remember a list of words, it also eliminates the word length effect (Figure 5.12a). According to the word length effect, a list of one-syllable words should be easier to recall than a list of longer words because the shorter words leave more space in the phonological loop for rehearsal. However, eliminating rehearsal by saying “the, the, the . . .” removes this advantage for short words, so both short and long words are lost from the phonological store (Figure 5.12b). The Visuospatial Sketch Pad The visuospatial sketch pad handles visual and spatial information and is therefore involved in the process of visual imagery—the creation of visual images in the mind in the absence of a physical visual stimulus. The following demonstration illustrates an early visual imagery experiment by Roger Shepard and Jacqueline Metzler (1971). D E M O N S T R AT I O N Comparing Objects Look at the two pictures in Figure 5.13a and decide, as quickly as possible, whether they represent two different views of the same object (“same”) or two different objects (“different”). Also make the same judgment for the two objects in Figure 5.13b. When Shepard and Metzler measured participants’ reaction time to decide whether pairs of objects were the same or different, they obtained the relationship shown in Figure 5.14 for objects that were the same. From this function, we can see that when one shape was rotated 40 degrees compared to the other shape (as in Figure 5.13a), it took 2 seconds to decide that a pair was the same shape. However, for a greater difference caused by a rotation of Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 146 4/18/18 4:01 PM Working Memory : Manipulating Information Percent correct recall 100 Phonological loop Visuospatial sketch pad 50 the, the, the . . . 0 Short Long words words Articulatory suppression (a) 147 ➤ Figure 5.12 (a) Saying “the, the, the . . .” abolishes the word length effect, so there is little difference in performance for short words and long words (Baddeley et al., 1984). (b) Saying “the, the, the . . .” causes this effect by reducing rehearsal in the phonological loop. Reduces rehearsal advantage for short words (b) 5 Reaction time (sec) 4 (a) 3 2 1 0 (b) 0 20 40 60 80 100 120 140 160 180 Angular difference (degrees) ➤ Figure 5.13 Stimuli for the “Comparing Objects” demonstration. See text for details. ➤ Figure 5.14 Results of Shepard and Metzler’s (1971) mental rotation experiment. (Source: Based on R. N. Shepard & J. Metzler, Mental rotation of three-dimensional objects, Science, 171, Figures 1a & b, 701–703, 1971.) (Source: Based on R. N. Shepard & J. Metzler, Mental rotation of three-dimensional objects, Science, 171, Figures 1a & b, 701–703, 1971.) 140 degrees (as in Figure 5.13b), it took 4 seconds. Based on this finding that reaction times were longer for greater differences in orientation, Shepard and Metzler inferred that participants were solving the problem by rotating an image of one of the objects in their mind, a phenomenon called mental rotation. This mental rotation is an example of the operation of the visuospatial sketch pad because it involves visual rotation through space. Another demonstration of the use of visual representation is an experiment by Sergio Della Sala and coworkers (1999) in which participants were presented with a task like the one in the following demonstration. D E M O N S T R AT I O N Recalling Visual Patterns Look at the pattern in Figure 5.15 for 3 seconds. Then turn the page and indicate which of the squares in Figure 5.17 need to be filled in to duplicate this pattern. ➤ Figure 5.15 Test pattern for visual recall test. After looking at this for 3 seconds, turn the page. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202 08271_ch05_ptg01.indd 147 4/18/18 4:01 PM 148 CHAPTER 5 Short-Term and Working Memory In this demonstration, the patterns are difficult to code verbally, so completing the pattern depends on visual memory. Della Sala presented his participants with patterns ranging from small (a 2 3 2 matrix with 2 shaded squares) to large (a 5 3 6 matrix with 15 shaded squares), with half of the squares being shaded in each pattern. He found that participants were able to complete patterns consisting of an average of 9 shaded squares before making mistakes. The fact that it is possible to remember the patterns in Della Sala’s matrix illustrates the operation of visual imagery. But how could the participants remember patterns consisting of an average of 9 squares? This number is at the high end of Miller’s range of 5 to 9 and is far above the lower estimate of four items for STM from Luck and Vogel’s experiment (Figure 5.8). A possible answer to this question is that individual squares can be combined into subpatterns—a form of chunking that could increase the number of squares remembered. Just as the operation of the phonological loop is disrupted by interference (articulatory suppression, see page 146), so is the visuospatial sketch pad. Lee Brooks (1968) did some experiments in which he demonstrated how interference can affect the operation of the visuospatial sketch pad. The following demonstration is based on one of Brooks’s tasks. O D E M O N S T R AT I O N ➤ Figure 5.16 “F” stimulus for Holding a Spatial Stimulus in the Mind demonstration illustrating outside (O) and inside (I) corners. Read the directions in the text, then cover up the F. (Source: From Brooks, 1968) Holding a Spatial Stimulus in the Mind This demonstration involves visualizing a large “F” like the one in Figure 5.16, which has two types of corners, “outside corners” and “inside corners,” two of which are labeled. Task 1: Cover Figure 5.16, and while visualizing F in your mind, start at the upper-left corner (the one marked with the o), and, moving around the outline of the F in a clockwise direction in your mind (no looking at the figure!), point to “Out” in Table 5.2 for an outside corner and “In” for an inside corner. Move your response down one level in Table 5.2 for each new corner. Task 2: Visualize the F again, but this time, as you move around the outline of the F in a clockwise direction in your mind, say “Out” if the corner is an out