Memory Errors, Memory Gaps
Memory Errors, Memory Gaps
Memory Errors, Memory Gaps Where did you spend last summer? What country did you grow up in? Where were you five minutes ago? These are easy questions, and you effortlessly retrieve this information from memory the moment you need it. If we want to understand how memory functions, therefore, we need to understand how you locate these bits of information (and thousands of others just like them) so readily. Memory Errors, Memory Gaps
But we also need to account for some other observations. Sometimes, when you try to remember an episode, you draw a blank. On other occasions, you recall something, but with no certainty that you’re correct: “I think her nickname was Dink, but I’m not sure.” And sometimes, when you do recall a past episode, it turns out that your memory is mistaken. Perhaps a few details of the event were different from the way you recall them. Or perhaps your memory is completely wrong, misrepresenting large elements of the original episode. Worse, in some cases you can remember entire events that never happened at all! In this chapter, well consider how, and how often, these errors arise. Let’s start with some examples. Memory Errors: Some Initial Examples In 1992, an El Al cargo plane lost power in two of its engines just after taking off from Amsterdam’s Schiphol Airport. The pilot attempted to return the plane to the airport but couldn’t make it. A few minutes later, the plane crashed into an 11-story apartment building in Amsterdam’s Bijlmermeer neighborhood. The building collapsed and burst into flames; 43 people were killed, including the plane’s entire crew.
Ten months later, researchers questioned 193 Dutch people about the crash, asking them in particular, “Did you see the television film of the moment the plane hit the apartment building?” More than half of the participants (107 of them) reported seeing the film, even though there was no such film. No camera had recorded the crash; no film (or any reenactment) was shown on television. The participants seemed to be remembering something that never took place (Crombag, Wagenaar, & van Koppen, 1996). Memory Errors, Memory Gaps
In a follow-up study, investigators surveyed another 93 people about the plane crash. These people were also asked whether they’d seen the (nonexistent) TV film, and then they were asked detailed questions about exactly what they had seen in the film: Was the plane burning when it crashed, or did it catch fire a moment later? In the film, did they see the plane come down vertically or did it hit the building while still moving horizontally at a considerable with no forward speed speed? Two thirds of these participants reported seeing the film, and most of them were able to provide details about what they had When asked about the plane’s speed, for example, only 23% said that they couldn’t remember. The others gave various responses, presumably based on their “memory” of the (nonexistent) film. Memory Errors, Memory Gaps
Other studies have produced similar results. There was no video footage of the car crash in which Princess Diana was killed, but 44% of the British participants in one study recalled seeing the footage (Ost, Vrij, Costall, & Bull, 2002). More than a third of the participants questioned about a nightclub bombing in Bali recalled seeing a (nonexistent) video, and nearly all these participants reported details about what they’d seen in the video (Wilson & French, 2006). Memory Errors, Memory Gaps
It turns out that more persistent questioning can lead some of these people to admit they actually don’t remember seeing the video. Even with persistent questioning, though, many participants continue to insist that they did see the video-and they offer additional information in the film (e.g., Patihis & Loftus, 2015; Smeets et al., 2006). Also, in all about exactly what they sav these studies, let’s emphasize that participants are thinking back to an emotional and much- discussed event; the researchers aren’t asking them to recall a minor occurrence.
Is memory more accurate when the questions come after a shorter delay? In a study by Brewer and Treyens (1981), participants were asked to wait briefly in the experimenter’s office prior to the procedure’s start. After 35 seconds, participants were taken out of this office and told that there actually was no experimental procedure. Instead, the study was concerned with their memory for the room in which they’d just been sitting. Participants’ descriptions of the office were powerfully influenced by their prior beliefs. Surely, most participants would expect an academic office to contain shelves filled with books. In this particular office, though, no books in view (see Fiqure 8.1). Even so, almost one third of the participants (9 of 30) reported seeing books in the office. Their recall, in other words, was governed by their expectations, not by reality. How could this happen? How could so many Dutch participants be wrong in their recall of the plane crash? How could intelligent, alert college students fail to remember what they’d seen in an office just moments earlier? Memory Errors: A Hypothesis In Chapters 6 and 7, we emphasized the importance of memory connections that link each bit of knowledge in your memory to other bits. Sometimes these connections tie together similar episodes, so that a trip to the beach ends up connected in memory to your recollection of other trips. Sometimes the connections tie an episode to certain ideas-ideas, perhaps, that were part of your understanding of the episode, or ideas that were triggered by some element within the episode.
It’s not just separate episodes and ideas that are linked in this way. Even for a single episode, the elements of the episode are stored separately from one another and are linked by connections. In fact, the storage is “modality-specific,” with the bits representing what you saw stored in brain areas devoted to visual processing, the bits representing what you heard stored in brain areas specialized for auditory processing, and so on (e.g., Nyberg, Habib, McIntosh, & Tulving, 2000; Wheeler Peterson, & Buckner, 2000; also see Chapter 7, Figure 7.4, p. 245).
With all these connections in place-element to element, episode to episode, episode to related ideas-information ends up stored in memory in a system that resembles a vast spider web, with was the each bit of information connected by many threads to other bits elsewhere in the web. This idea that in Chapter 7 we described as a huge network of interconnected nodes. However, within this network there are no boundaries keeping the elements of one episode separate from elements of other episodes. The episodes, in other words, aren’t stored in separate “files,” each distinct from the others. What is it, therefore, that holds together the various bits within each episode? To a large extent, it’s simply the density of connections. There are many connections linking the various aspects of your “trip to the beach” to one another; there are fewer connections linking this event to other events.
As we’ve discussed, these connections play a crucial role in memory retrieval. Imagine that you’re trying to recall the restaurant you ate at during your beach trip. You’ll start by activating nodes in memory that represent some aspect of the trip-perhaps your memory of the rainy weather. Activation will then flow outward from there, through the connections you’ve established, and this will energize nodes representing other aspects of the trip. The flow of activation can then continue from there, eventually reaching the nodes you seek. In this way, the connections serve as retrieval paths, guiding your search through memory.
Obviously, then, memory connections are a good thing; without them, you might never locate the information you’re seeking. But the connections can also create problems. As you add more and more links between the bits of this episode and the bits of that episode, you’re gradually knitting these two episodes together. As a result, you may lose track of the “boundary” between the episodes. More precisely, you’re likely to lose track of which bits of information were contained within which event. In this way, you become vulnerable to what we might think of as “transplant” errors, in which a bit of information encountered in one context is transplanted into another context. In the same way, as your memory for an episode becomes more and more interwoven with other thoughts you’ve had about the event, it will become difficult to keep track of which elements are were actually part of the episode itself, and which are linked merely because they were associated with the episode in your thoughts. This, too, can produce linked to the episode because they transplant errors, in which elements that were part of your thinking get misremembered as if they were actually part of the original experience. Understanding Both Helps and Hurts Memory It seems, then, that memory connections both help and hurt recollection. They help because the connections, serving as retrieval paths, enable you to locate information in memory. But connections can hurt because they sometimes make it difficult to see where the remembered episode stops and other, related knowledge begins. As a result, the connections encourage intrusion errors-errors in which other knowledge intrudes into the remembered event.
To see how these points play out, consider an early study by Owens, Bower, and Black (1979). In this study, half of the participants read the following passage:
Nancy arrived at the cocktail party. She looked around the room to see who was there. She went to talk with her professor. She felt she had to talk to him but was a little nervous about just what to say. A group of people started to play charades. Nancy went over and had some refreshments. The hors d’oeuvres were good, but she wasn’t interested in talking to the rest of the people at the party. After a while she decided she’d had enough and left the party.
Other participants read the same passage, but with a prologue that set the stage:
Nancy woke up feeling sick again, and she wondered if she really was pregnant. How would she tell the professor she had been seeing? And the money was another problem.
All participants were then given a recall test in which they were asked to remember the sentences as exactly as they could. Table 8.1 shows the results-the participants who had read the prologue (the Theme condition) recalled much more of the original story (i.e., they remembered the propositions actually contained within the story). This is what we should expect, based on the claims made in Chapter 6: The prologue provided a meaningful context for the remainder of the story, and this helped understanding. Understanding, in turn, promoted recall.