Why We Forget and How to Remember Better, page 13
When memory structures get built (encoded) and stuck together (stored) with their rooms (the details) all interconnected, at retrieval you can often use memory for one detail to help you retrieve other, associated details. In the example at the beginning of this chapter, once memory for the birthday party returned to your mind, so did your memory for other details about your prior encounter with the woman. It’s as if standing in one room of your memory structure can reveal the corridor that can lead you into another room with another set of details.
But sometimes the prefrontal cortex or hippocampus fails to do its job. Often, the failure is at retrieval: The rooms and corridors exist, but the prefrontal cortex and hippocampus don’t work together to allow the hippocampal index (described in Chapter 4) to reveal them. It’s as if you’re looking at the memory structure from a distance: You have only a vague feeling of familiarity, without any details. These failures are often transient, as in the example at the start of the chapter. Eventually, with the right retrieval cue, you’re suddenly able to step into the relevant memory structure, moving beyond this feeling of familiarity as you recall more and more of the details.
At other times, the prefrontal cortex or hippocampus fails to do its job in the earlier stages of memory creation or storage. Perhaps the scaffolding for the memory structure is built but the rooms are not constructed. Or maybe the rooms are crafted but never adequately linked together. In these cases, you can still recognize that you’ve seen someone or something before—you have that feeling of familiarity—but you can’t retrieve the details. You might wander down a street, realizing you’ve been there before, but unable to remember when. Or you might have a conversation that begins like the one outlined at the start of this chapter but ends with you still unable to recall the details of your past encounter—and without any details about this person who clearly knows you.
Types of Associations
There are many different types of information that you may want to build into your memory structure. They are similar in that they require the prefrontal cortex to select those details as important to be included in the memory structure and the hippocampus to serve as the Velcro—keeping those details bound within the structure. But each type of detail requires slightly different strategies for getting it into or out of your memory.
Name That Source
You often need to create a link between a piece of information and the context in which you encountered it. Did you learn something from a news outlet you trust, or was it from a social media post? Which parent told you about their child’s trip to the emergency room due to a nut allergy? These details can be critical for good decision-making: Should you repeat the story to a colleague? Can you serve Nutella at tonight’s event?
Despite their importance, these source details often don’t get built into memory structures.2 Attention to other details is often the cause. As you were reading the story, you might not have given much thought to its source, and so that detail may never have been committed to memory. As you were listening to the parent talk about their child, you may have been focused on the harrowing details of the event, rather than on who was telling the story. Building the source into your memory structure often takes extra effort. You can’t take it for granted that you will be able to remember who said what, when, and where. If those details matter, you need to attend to them and take extra effort to commit them to memory.
Even if the source details do get incorporated into your memory structure, it takes additional effort at retrieval to bring them to mind again. So, if you’re rushed or stressed—factors that tend to push you toward faster, less effortful ways to retrieve information from memory—you’re more likely to just repeat the story you read, without considering whether it was from a trustworthy source. When the stakes are high (as in the nut allergy example), it can be important to slow down and give yourself a moment to check your mental sources before using or sharing the content you have stored in memory.
Who Did I Tell?
A related type of association is not who told you something, but to whom you told something. Have you ever launched into a story and—when you’re halfway through—wondered if this is the second time you’re telling it to this friend? Errors in destination memory3 can become exacerbated as adults grow older, and they become even more pronounced with Alzheimer’s disease or other forms of dementia (see Chapter 13). But all of us can suffer from these lapses. As with source memory errors, often the lapses result from inattention to the destination details: You may have been so caught up in relaying the story in just the right way that you didn’t really focus on your audience. Other times, the problem is that you fail to monitor your memory for those details: Had you taken an extra moment to think back to when you’d previously told the story, you would have remembered telling it to this friend. But the story fit so well with the topic of conversation that, instead, you quickly jumped into its (re)telling.
Actions Versus Imaginations
You are driving to the airport and suddenly think: “Did I pack my passport—or did I only think about doing it?” Despite how important it is to determine whether you performed an action or only imagined it, it is often difficult to distinguish between these possibilities. There is tremendous overlap between how you use your brain to imagine an action and how you use your brain to actually perform that action. It takes about the same amount of time to imagine an action as to actually perform it, and similar brain networks are recruited whether you imagine or execute the action. This is one reason why, as described in Chapter 2, imagining motor actions can help us to improve at those skills. This similarity also means a memory for an imagined action will have a similar structure to a memory for a performed action—which can make them hard to distinguish from one another.
You can make the distinction a bit easier if, as you perform an action, you pay attention to features that you would be unlikely to imagine. As you pack your passport, you can pay attention to the texture of the passport cover, compare its size to the palm of your hand, and attend to how it looks placed in its safe location in your bag. You can also make it less likely that you will confuse your imaginings with reality if you build into your imagery some details that disconnect it from the present moment. For example, if you are imagining packing your passport as a way to help you remember to do so later, you might imagine yourself wearing a different outfit than the one you’re currently wearing or think about the importance of performing the action at a later time of day, when the sun is setting.
Ordering Events
What about if you need to associate events on a timeline or in chronological order, such as a sequence of historical events or your recent trip itinerary?
In some cases (such as the sequence of historical events), you may be able to build one memory structure that would contain all of those temporal relations. Many mnemonics are designed to help retrieve content in a particular order every time. For instance, the “peg word” technique is a mnemonic that has you first memorize 10 items in order (1 = gun, 2 = shoe, 3 = tree, etc.) and then imagine the content you want to remember as being associated with those words. For instance, if trying to memorize the order of certain battles in the Civil War, you might imagine the guns in use first at Fort Sumner, then associate shoe with the Battle of Bull Run, tree with the Battle of Seven Pines, and so forth (see Chapter 25 for discussion of mnemonic devices).
In other cases (such as recalling the order in which you saw various sights on a recent trip), the desired information is likely to be spread across multiple different memory structures that were built throughout your trip. Sometimes, the information contained within one of these memories contains clues to order. You may remember wearing a necklace to the theater, and if you also know you bought that necklace in a museum store on that same trip, you can determine that you visited the museum before the theater. Other times, to figure out the order, you need to compare across different memory structures, which can be quite challenging. Recent evidence suggests that one of the reasons you can sometimes figure out these timing comparisons is because cells in some portions of the hippocampus show gradual time-dependent changes in the ways that they respond.4 This means that a memory structure built on Day 1 of your trip will have a slightly different time signature than a memory structure built on Day 2, providing a kind of time-stamp to our memories. But gaining conscious access to those time signatures appears to be difficult, and time perception errors in memory abound.
Once More, with Feeling
Sometimes, what you want to remember is the emotion associated with an event. How did you feel on your graduation day? The emotions tied to an event are thought to exist in the amygdala (an almond-shaped structure just in front of the hippocampus) or in connections between the hippocampus and the amygdala. But, unlike other types of details that we’ve described, these features are subjective, and thus the emotions that you conjure when recalling a memory can have as much to do with your current emotional state as with the one you were in at the time the event occurred. If you have felt better about an event after talking about it with a friend, you recognize that the emotions tied to memories are malleable. Fortunately, over time, negative emotions are particularly likely to fade,5 perhaps related to sleep (see Chapter 20). You might know that you were seething with anger during an argument but, years later, it is unlikely that you will fully re-experience that anger when reflecting back on the exchange.
The elicitation of strong emotions during an event can also affect the likelihood that other event details are remembered. There is still much ongoing work on this topic, but there is reason to think that negative emotions tend to “telescope” memories, giving good resolution to details linked to the negative experience (you might remember your friend’s tone of voice or the look on her face during the argument) at the expense of other details (you may have no idea where the argument took place or who else was in the room).6 Positive emotions may instead broaden the scope of the memory, making it easier to link together otherwise unrelated event elements.
The Importance of Keeping It Together
Retaining the details of past events can be essential for good decision-making. The examples we’ve described highlight that it’s often insufficient to have a single piece of information in mind to make the right decision. You also need to evaluate whether you should trust that piece of information, share it with someone, or follow through on an intention. In addition, there are other times when additional details serve as important building blocks for other key functions of memory.
Building Inferences
Inferences allow you to build upon your prior knowledge to make sense of the present moment. The root of inferential learning is your ability to form associations in memory—and then to pull those associations back out of your memory when needed. This ability can be a key to learning in classroom settings as well as in daily life.
If you see a child being picked up at daycare by a man one day and by a woman the next day, you probably wouldn’t be surprised to later see the man and woman together. You would have effortlessly made the inference that they know one another, through their shared association with the child,7 without needing to see them together. But that inference—that new association between the man and the woman—can only be made if, upon seeing the child with the woman, you remember previously seeing the child with the man.
Similarly, if you see a woman holding a diaper, you can use your preexisting knowledge to infer that there is a baby nearby, even if you never see that baby. But again, that inference can only be made if you’ve built a strong association between diapers and babies; if that association isn’t brought to mind, then the inference can’t be made.
Update That Memory
Associating details together also helps to keep our memories up to date. Your friend may have pursued a PhD in biology, but later decided to change career paths to become a photographer. Another friend may have married, taking her spouse’s last name. In both cases, you must update your knowledge about your friend, creating a new association. Equally importantly, you want those new associations to be the ones that come to mind—rather than the older ones—so that you don’t continue to ask your one friend about her latest biology experiment or refer to your other friend by her maiden name. Fortunately, the time signatures in the hippocampus that we described earlier can help with this: The memory structures that have a time signature closer to the present moment will generally come to mind first, allowing you to remember which is your friend’s current career or last name.
How to Keep It Together
Now that you know how important it can be to remember the details, here’s what you can do to more effectively build those details into your memory structure and access them when needed.
• Attend to the details you want to remember. Does this advice sound familiar? We keep repeating it because it is so important. If you don’t want to forget where you read a story, be sure to attend to your sources. Pay attention to the title of a book or to the outlet you’re reading online. If you don’t want to tell the same story to the same person twice, pay close attention to who is with you as you tell the story; closely considering their facial expressions and reactions to the story will help. If you’re at a specific event (perhaps a wedding or a reunion), make a mental note of the occasion on which you’ve told the story.
• Link the details together. It’s hard to create a mental structure that consists of unrelated content, so put in the effort to connect the details. Build those corridors that can connect one room of your structure to the next. Both the corridors and the effort of building them will help.
◦ Do this verbally: It can be something as simple as saying aloud, “I’m putting my keys on the dresser,” or repeating the phrase, “key–dresser.” Or try creating a novel statement like, “My dresser holds the key.”
◦ Use mental imagery: Imagine standing on top of a mountain with the new acquaintance with whom you’re discussing your enjoyment of hiking.
◦ Use mnemonic devices: If you find yourself often needing to remember associations or long lists of information, you may benefit from taking the time to train yourself in the use of mnemonic devices. See Chapter 25.
• Try different retrieval cues. As you try to find your keys, imagine yourself coming home earlier or actually retrace your footsteps as you walked in the door. If you’re trying to remember who told you about their child’s nut allergy, bring to mind any details you do remember: Where did you have the conversation? What else did you talk about with this parent?
• Stay calm. We’ve said this before, but it bears repeating: Stress is particularly harmful for constructing—and reconstructing—memory structures that contain all the relevant details. We fully recognize it can be difficult to stay calm as you’re rushing to find your misplaced keys or feeling uneasy when you can’t recall where you met someone. But take a deep breath, remember that memory lapses like these are common and often transient, and focus on what you can do in the moment—like trying those different retrieval cues.
11
Control what you forget and remember
It’s your first day at a new job, and as you walk into a conference room, you trip over a power cable and nearly fall. You feel yourself blush and hope that not too many people saw the stumble. The next day, as you walk into the conference room, you think of this unpleasant moment. This is one memory you’d like to forget. If only there were a way to stop unwanted memories from coming to mind!
Would you like to be able to control what you remember and what you forget?
You may often think about forgetting as a consequence of having an imperfect memory system. But sometimes, as in the example above, you may be particularly motivated to forget information: You may not want an unpleasant event to spring to mind at inopportune moments, or you may recognize that information is unimportant and not worth remembering. In this chapter, we’ll explore the extent to which you can control what you remember—and what you forget.
Controlling What Details Go into Memory
As a college professor, Elizabeth knows that few things can get students to pay attention like saying, “This is going to be on the exam.” Although you can be imperfect in implementing your plans, you know that when something is important to remember, you should pay attention. More generally, when you know there is value to information—that it will help you on a later exam or job interview—your brain prioritizes getting that information into your memory. There are specialized neural circuits that are engaged by reward that can enhance your ability to get information into memory, making it more likely that the hippocampus does a good job and builds a memory structure replete with details.
Tag It in the Past
You can even learn after an event is over that its details were important, and that knowledge can increase the likelihood those details will be sustained over time in the memory structure you built.1 Imagine leaving your eighth-floor office and walking home, only to find upon arriving at your front door that you’ve lost your keys. Suddenly, details of your chosen path that may have seemed irrelevant at the time—which elevator you rode down to the lobby, which side of the road you walked along—take on a new importance. At least for a while after an event has occurred, you can reprioritize event details, bringing to the forefront details that you suddenly realize have high importance.
