Why do we remember some things and not others? How much can we remember and how long can our memories last? What processes shape our memory of the world? Memories are a fundamental part of who we are, so it's natural that we should have so many questions about why some memories persist while others fade, or how it is that we can win a game of Trivial Pursuit and on the same night forget where we left our keys.

We can think of the memory process as having three distinct phases: encodingencodingThe process of getting information into memory — converting sensory input into a neural code., storagestorageThe retention of encoded information over time., and retrievalretrievalThe process of accessing and bringing stored information back into conscious awareness.. You'll notice that these words are shared with computer terminology and this is a result of a shift in thinking during the 1950s and 1960s as psychology began to think of the mind as being similar to a computer in how it processes information.

Encoding refers to the process of transforming information into a memory or creating a new memory.

Storage refers to maintaining the memory over time, whether that means holding onto it for a few minutes or for a lifetime.

Retrieval refers to getting access to a memory that has been stored.

As we'll see throughout this chapter, failures are possible at any of these steps in the memory process. These different types of memory failures will have different characteristics, depending on whether encoding, storage, or retrieval has been affected. We'll also look at how mnemonic techniques can be used to help reduce memory failure and how knowing more about how your memory works can help you to use it more effectively.

Let's begin with a fairly simple model for our different types of memory. The 3-Box information processing model proposed by Richard Atkinson and Richard Shiffrin divides memory into 3 types: sensory memorysensory memoryA very brief, high-capacity memory system that holds sensory impressions for a fraction of a second., short-term memoryshort-term memoryThe memory system that temporarily holds a limited amount of information for active use — capacity ~7 items, duration ~20-30 seconds., and long-term memorylong-term memoryThe memory system with essentially unlimited capacity that stores information for extended periods.. While the latter two types may be familiar to you in everyday use, you may not be familiar with the first type.

Sensory memory is the first “box” in this model. Sensory memory is a highly detailed and accurate representation of information from our senses, which only lasts for about a second. Because it lasts so briefly, it’s difficult to study sensory memory, but George Sperling devised a clever way to investigate it. Sperling showed participants a slide containing 3 rows of 4 letters (such as below) for only 1/20 of a second.

He then immediately asked the participants to recite what they saw on either the top, middle, or bottom row. He found that participants were generally able to recall any row he asked for with near perfect accuracy, provided that he asked immediately (errors quickly increased if the delay was 1 second or longer). Participants were essentially “reading” the letters off of a fleeting mental image and this short-lived visual information store is known as iconic memoryiconic memoryVisual sensory memory — holds a snapshot of visual information for less than a second. (while auditory sensory memory is referred to as echoic memoryechoic memoryAuditory sensory memory — holds sound information for a few seconds.). This research indicates that the sensory memory store actually contains all of the letters, but that this storage lasts very briefly. Despite their ability to recall any row requested, the participants weren’t able to recall all of the rows. The sensory memory store dissipates so quickly that in the time it took to recite one row, the others had disappeared from memory and could no longer be recalled accurately.

By focusing their attention on one of the rows (the one requested) participants were able to store that information a bit longer. This also demonstrates the role of selective attention in memory storage. We can only pay attention to a small amount of the information in our sensory memory at once, and this dictates which information will make its way to the next “box” of the 3-box model: short-term memory.

Research by George Miller has estimated that short-term memory can hold somewhere between 5 to 9 items (described in a classic paper titled: The Magical Number 7 Plus or Minus 2). When asked to recall a list of words, a string of digits, or a sequence of colors, most people do fine up to about 7 items, after which accuracy drops off sharply. This “magical number 7″ can be extended through the use of mnemonic techniques such as looking for relationships and patterns among items or creating stories. These techniques are known as organizational encoding. One particular type of organizational encoding, known as chunkingchunkingOrganizing individual items into larger meaningful units to expand effective working memory capacity., consists of placing multiple items into groups. For example, if you wanted to remember the number 2317761945007 rather than think of individual digits you might create chunks you recognize such as “Michael Jordan’s jersey #”, ”Declaration of Independence signed”, “End of WWII”, and “James Bond's agent number” allowing you to recall all 13 digits while only needing to remember 4 items.

Short-term memory only lasts for about 10-30 seconds, but this can be extended by rehearsal; mentally repeating the items to keep them from fading. This is essentially a way of re-inputting the information into sensory memory, allowing us to repeat the cycle. If attention is divided or distracted, however, rehearsal will no longer be effective. You may have experienced this if you’ve ever been interrupted while mentally trying to repeat a phone number. Since Atkinson and Shiffrin first proposed the 3 box model, some changes have been made, including the addition of the term working memoryworking memoryAn updated model of short-term memory emphasizing active manipulation of information — includes a central executive and rehearsal loop.. Working memory refers to information in short-term memory that is currently being manipulated. For example, when you are attempting to add several numbers, like solving 478 plus 23, you need to hold each of these numbers in your mind, but you also need to be able to work with them and keep track of changes.

The final memory store in the 3-box model is long-term memory. There isn’t a known capacity limit for human long-term memory, so there isn’t a point at which your memory can be considered “full” and you can no longer encode any new memories. The duration of long-term memory varies greatly; some items may be held for a matter of hours, others for a lifetime.

Long-term memories can be divided into 3 main types: episodic, semantic, and procedural. Episodic memories are sequential events and narrative stories that make up your own personal history. These might include memories of your third-grade class, a first date, or a vacation. These are generally remembered as a “gist” of the story and not as a list of specific facts. So when I ask you about your vacation, your episodic memoryepisodic memoryExplicit memory for personal experiences and autobiographical events. allows you to give a general description of the overall experience.

Semantic memorySemantic memoryExplicit memory for general facts and knowledge about the world. consists of factual knowledge of the world; names, dates, word meanings, categories, etc. Both episodic and semantic memories are examples of explicit (or declarative) memories because they can be consciously recalled and described.

Procedural memoryProcedural memoryImplicit memory for motor skills and habitual behaviors — knowing how to ride a bike. is a memory for skills and how to perform them. These memories can be demonstrated but may be rather difficult to put into words or be consciously described. For this reason, procedural memory is often considered a type of implicit (or non-declarative) memory because you may not need to consciously recall it in order to perform the behavior. In fact, you may not even be consciously aware that the memory exists. For instance, you can probably effortlessly tie your shoes, but if you were asked to consciously describe each step of tying your shoes, you might find it difficult. You may even need to perform the behavior and then narrate what you see your hands doing. This divide between our memory of how to do things and how to consciously describe how we do those things can provide insight into the complexity of teaching physical tasks. These different types of memory explain why someone may be able to perfectly execute a complex maneuver, but find themselves at a complete loss for words when it comes to describing exactly what they are doing.

Despite the shared terminology with computers, our memory doesn’t work like a hard drive, neatly and accurately storing information to be called up later. Our memory is subject to error, either at the level of encoding, storage, or retrieval, resulting in several different types of failures, which Harvard professor Daniel Schacter refers to as the “Seven Sins of Memory” : Transience, Absentmindedness, Blocking, Misattribution, Suggestibility, Bias, and Persistence.

Transience is a failure of retrieval that results from the passage of time. The German researcher Hermann Ebbinghaus worked to quantify how much memory faded (and how quickly it faded) by repeatedly testing himself with lists of nonsense syllables made by placing a vowel between two consonants (creating “words” like DEK, PUV, DUT, etc.). Based on his data, he described a “forgetting curve” which showed that a great deal of information is lost rather quickly, and then the rate of information loss slows and the curve gradually flattens.

The inevitably transient nature of our memory highlights the importance of regular review for memories we wish to maintain. By repeatedly reviewing information, we can gradually raise the curve and increase our retention. In the Improve Your Memory section at the end of this chapter we'll go into more detail on how to maximize the effectiveness of your review to reduce transience.

Absentmindedness is a type of forgetting that occurs due to a lapse in attention. If you’ve ever forgotten an umbrella in a restaurant or a bag in a taxi, you’ve experienced absentmindedness. It generally isn’t the case that the memory has been completely forgotten (since it is often recalled just moments later) but rather that our attention is momentarily placed elsewhere and so we fail to bring the memory to mind when we need it. We can think of this as a type of retrieval error, because even though the memory has been encoded and stored accurately (as evidenced by our later recall) we fail to retrieve the memory at the appropriate time.

Knowing that our future self may fail to remember something at the appropriate time and then making plans to prevent this from occurring is referred to as prospective memory; memory for the future. This is planning a reminder for something that will force our attention to retrieve the memory at the appropriate time. For instance, if you're worried about forgetting to bring an important bag with you tomorrow morning, you might place the bag in front of the door tonight. This will ensure that you see the bag as you are leaving in the morning, directing your attention to retrieve the appropriate memory (bring this with me) at the appropriate time (and not 20 minutes later when you are half-way to your destination).

Blocking occurs when we have a memory but are temporarily unable to successfully retrieve it. This may cause a “tip-of-the-tongue” experience; the frustrating condition in which we know that the memory is there even though we can’t bring it to mind. We know that we have encoded and stored the memory, so the error is at the level of retrieval. This tip-of-the-tongue experience can be triggered when we attempt to retrieve memories that are infrequently accessed, such as when trying to recall the word for a person who makes maps, or when trying to remember the name of a former classmate.

Misattribution occurs when we incorrectly identify where a memory came from. We have the memory, but we think it came from somewhere else. If you start telling a juicy story to a friend and are interrupted by “I'm the one who told you that yesterday”, misattribution is to blame. Misattribution reveals that our brains aren’t particularly good at source memory, or memory for where information came from. So while we may correctly encode an interesting fact, we may have trouble recalling whether a friend told us, we read it on a blog, or saw it in a YouTube video. This memory error can be particularly troublesome in the courtroom, as eyewitnesses may incorrectly identify innocent bystanders as perpetrators (because they recognize their faces) or even falsely accuse others they recognize from completely different circumstances.

A famous (and somewhat ironic) example of this occurred when a woman accused Donald Thomson of rape. Thomson's alibi was sound, as he was at a television studio filming a live broadcast when the crime occurred. The woman had actually been watching the program prior to her attack, and she misattributed her memory of Thomson's face to that of her attacker. The irony is that in his television appearance, Thomson, a psychologist, was discussing eyewitness memory for faces.

Advertisers use our poor source memory to their advantage, as they blatantly sing the praises of their own products. While this type of blow-hard bravado may seem in poor taste, later we may recall hearing positive messages about a product, though we've forgotten that we heard those good things from the very company selling the product.

Misattribution can also occur in the form of false recognition, when a novel stimulus is similar enough to a previously-seen stimulus that we think they are the same. So we may believe that we recognize someone or something that we haven't actually seen before. This false recognition has been proposed as one possible explanation for the phenomenon of déjà vudéjà vuThe eerie sense of having experienced something before, thought to result from overlap between a current experience and a stored memory., as a new experience may trigger feelings of familiarity because it resembles a previous experience. In contrast, we may occasionally suffer from cryptomnesia, when we believe that a thought is new, when actually it is a memory of an old thought. This can lead to inadvertent plagiarism; we think an idea came from our own creative processes, but in fact it is a memory of someone else's work. Authors and musicians may be heartbroken (and legally liable) upon the realization that a wonderful turn of phrase or catchy riff is not a sign of their genius and creativity, but rather, a sign of their source memory's fallibility.

Suggestibility is the idea that external information can infiltrate and modify our memories, even implanting memories that weren’t there in the first place. In a number of studies, Elizabeth Loftus and colleagues have demonstrated that leading questions can change existing memories and false memories can be successfully created via suggestion. In one study, Loftus and John Palmer found that participants’ estimates of vehicle speed in a video of a car accident were influenced by the use of “smashed” vs. “hit” in the question (speed estimates rose significantly when participants were asked about cars that “smashed into each other”).

In another study, Loftus was able to successfully implant the false memory of being lost in a shopping mall as a child into the minds of several of her participants. These studies on suggestibility cast doubt on how much we can trust our own memories. We should remember that our memories are not recordings of events, but rather, reconstructions of events and we are always prone to the possibility of error each time we try to mentally put the pieces together.

Our memory is also subject to bias. We tend to reconstruct our past so that it seems more like our present (known as consistency bias) and we also tend to selectively recall memories that make us look better (known as egocentric bias), such as when college students who were asked to recall their high school transcripts tended to successfully recall the high grades but forgot more of the low grades they had received. This may be a bias that's not so bad, as there might be practical implications for our self-esteem. Egocentric bias may help ensure we recall our previous successes and minimize our failures, helping us feel more capable and motivated.

The final “sin” of memory from Schacter's list is when intrusive memories are brought to mind repeatedly and without conscious control, known as persistence. Flashbacks of negative events and traumatic experiences can repeatedly disrupt the minds of victims, interfering with their lives. Persistence demonstrates the powerful and sometimes painful connection between emotion and memory. We may consider the role of persistence in syndromes such as Post-Traumatic Stress Disorder (PTSD) in which patients feel trapped reliving the same traumatic event over and over again.

Those with PTSD may represent the extreme of persistence but for all of us, emotional events tend to be remembered better than non-emotional events. This can be seen in flash-bulb memories; detailed memories of emotionally-charged events. I can recall exactly where I was on the morning of September 11, 2001, and that’s an example of a flash-bulb memory. I can remember more details of that morning than some other non-emotionally-charged morning of say October 7, 2007. This isn’t to say that my memories of September 11th aren’t still subject to all of the other potential errors and biases above, but rather that the emotional intensity of that particular morning partially explains why it is more memorable and why memories of that particular morning may be brought to mind more often.

Our physical and emotional state plays a role not just in encoding memories, but also in their retrieval, as our current state prepares us to recall events from similar physical and emotional states. This is known as state-dependent memory. For example, when we're brimming with enthusiasm and motivation, we're more likely to recall memories filled with optimism and excitement, but when we're feeling down it's easier to recall past experiences of sadness and disappointment. This has important implications for the treatment of disorders like depression because it may contribute to a downward spiral as depressed patients are more likely to recall negative memories and experiences, further reducing their mood.

One major breakthrough in understanding brain structures and memory came from the case of H.M., a patient who had the hippocampus surgically removed from both sides of his brain to reduce epileptic seizures. Following his surgery, which was successful in reducing seizures, H.M. was unable to form new memories, a condition known as anterograde amnesiaanterograde amnesiaThe inability to form new long-term memories following brain damage.. While hippocampectomy is rare, other patients with hippocampal damage from injury or infection have provided similar case studies. These cases also provide evidence that long-term memory is a separate store of memory in the 3-box model, since these patients have intact sensory and short-term memory. They can repeat lists of words, copy diagrams, and answer questions, but they cannot move this information to long-term memory. Just moments later they won’t remember the words in the list, the fact that they had been drawing, or even what question they are in the middle of answering.

There is some evidence, however, that they are able to retain some long-term memory in the form of procedural memories. H.M. was able to improve his ability in certain types of physical tasks (such as drawing while looking in a mirror) even though he couldn’t consciously remember practicing the tasks. It appears that the cerebellum, basal ganglia, and striatum are crucial structures in the formation and storage of these types of procedural memories, which is why H.M. was still able to learn them despite lacking functioning hippocampi.

The case of Clive Wearing, a British musicologist who received damage from a brain infection, is even more severe, because in addition to anterograde amnesia he suffers extensive retrograde amnesiaretrograde amnesiaThe loss of memories that were formed before a brain injury., or loss of existing memories. He has almost no prior declarative memories, and, being unable to form new memories, this leaves him with only the present moment. He has functioning sensory memory and short-term memory, but no ability to create new long-term memories and very little ability to retrieve old long-term memories. This means that he is mentally living in a brief window of time, lasting only a matter of seconds. He does have procedural memories intact, as he can still speak and use language correctly, walk and move normally, and even play the piano. As with the cases above, this suggests that procedural memories must be stored and organized differently than other types of long-term memory.

Synaptic activity between two neurons can lead to a strengthened connection between those two neurons, known as Long-Term PotentiationLong-Term PotentiationThe strengthening of synaptic connections with repeated stimulation — thought to be the cellular mechanism of learning and memory. (LTP). This is often summarized with the expression “neurons that fire together wire together”. Even though these neurons don't actually “wire together” in terms of physically touching, the strength of their connection is increased via chemical interactions when they repeatedly fire synchronously. While the exact mechanisms of this process are not yet fully understood, there are several factors that are believed to be important. One possible signaling pathway is NMDA, for N-methyl-D-aspartate, a receptor for the neurotransmitter glutamate.

Repeated firing of a synapse causes the postsynaptic neuron to increase its number of glutamate receptors and this changes the postsynaptic neuron's sensitivity to future stimulation. Mice who have had an NMDA antagonist injected into their hippocampus have shown impaired spatial learning in a maze task (Morris, 1986). Ketamine, an anesthetic frequently used as a recreational drug, is an NMDA antagonist, explaining why one of its many effects is memory loss.

Understanding the neural aspects of memory formation also opens the possibility for the development of drugs to improve our memories. Mice given boosts to their NMDA levels show improved performance in learning tasks, so we may wonder whether human memory drugs will be hitting pharmacy shelves in the not-too-distant future. Until that day arrives, however, we'll need to rely on other methods of improving our memory, and fortunately humans actually have thousands of years of experience in this department.

My hope is that this section of the book is the most valuable and will help you to recall and apply the material from all of the other chapters. I think that it's best to have background understanding of the preceding material in this chapter first, so if you haven't already read the first half of this chapter, I highly recommend you do so before reading this section, as much of the terminology used here is explained there. Now let's look at how we can leverage our knowledge of memory to improve our ability to retain information. Along the way we'll learn a few more terms for some memory concepts, but with a focus on how they can be applied to mastering our own memory.

I want to keep this section practical and applicable, so I'm going to step back from explaining the details of the research supporting these principles. That said, if you are interested in more of the technicalities of this type of memory research, I encourage you to check the references section, where I've listed supporting studies for these concepts.

One of the first steps to improving memory is to organize the information that we want to recall. If I need to buy 15 items from the grocery store, rather trying to remember all items in a haphazard manner, organizing them by category would immediately improve my chances of recalling them correctly. Chunking these items into groups like vegetables, prepackaged foods, beverages, etc. provides a hierarchical structure that has been demonstrated to improve recall. Waiters and waitresses often use the same technique, organizing items by category, rather than blindly sticking to the mismatched sequence of items as customers placed their orders.

This may seem fairly obvious when it comes to grocery lists and entrees, but this organizational encoding can and should be applied to just about anything you want to remember. If you're looking to learn a bunch of SAT words you might start by organizing them into categories of nouns, verbs, and adjectives or maybe you'd prefer to break them into groups based on positive and negative connotations. There are any number of groupings that might make sense, you just want to avoid a chaotic jumble of terms.

While I've tried to organize terms in this book by related concepts, you might find that you remember them better by focusing on key individuals and the terms necessary for talking about their work. The type of organization you prefer is personal, but the key point is that you should have a structure in place. Later, once you have a good grasp of most of the information, you can shuffle your flashcards or pick out random terms to mix things up but this should be during review, not initial learning.

In the section on transience, we learned about the forgetting curve that Hermann Ebbinghaus created, but what wasn't mentioned is that Ebbinghaus also found recall tended to be better for certain items based on their location in his lists. He found that he was better able to recall the items at the beginning and the end of a list, known as the serial position effect. Improved recall for the initial items on a list is known as primacy, while the improvement for the final items of the list (which are most recent) is referred to as recency.

Imagine that you had a list of 20 items you wanted to recall. Serial position effects mean that you might recall the first few and last few terms better, but what about the 15 or so in the middle? Simply by breaking this list into 2 groups of 10 items, you'd be doubling your primacy and recency effects. And if you were to break those two lists down into smaller lists of just 5 items, you'd probably find your recall substantially improved without spending more time reviewing.

This is why it's important to take frequent breaks and to study material in small sections. Not only is it easier to stay focused and maintain your attention, but you also get the benefit of having more first items and more last items. Keep this in mind when you make your overly-ambitious study plans which include marathon cramming sessions. Rather than planning to slog your way through an entire book at once, plan to read just one section, then break, then return for the next section, etc. Provided that you keep returning (and those breaks don't turn into 4 hours of video games) you'll probably find that you're able to recall more of the material even after just one reading.

Students around the world may groan when they hear this, but testing does actually have benefits for memory, provided that you get a chance to see the answers and get feedback on your responses. This type of testing + feedback has been shown to improve recall more than simply having another review session and the resulting memory boost is known as the testing effecttesting effectThe finding that retrieving information from memory strengthens memory more than re-reading or re-studying.. We should take advantage of this by making all our review a type of test. This is why flashcards can be so much more effective than simply re-reading definitions. By forcing yourself to come up with an answer every time and then getting immediate feedback, you're able to get the testing effect many times over.

It's also a good idea to review often and in short sessions. This is known as distributed review and it has been shown to be more effective than long sessions or massed practice. Each time we review we raise that forgetting curve and slow the rate of its decline. There are a number of programs available which can schedule your review for you, known as spaced-repetition software or SRS (I personally use Anki and can recommend it). These programs calculate your next review based on your ranking of how well you remembered an item.

If you're sure that you've really learned everything, don't stop just yet. There's actually good reason to continue to review. Ebbinghaus found that transience decreased when he continued to review material that he already knew. This is known as overlearning and it should actually be a part of your study plans. Hopefully this will help you to pass your exams, but more importantly, help you to recall the material long after the exams have passed.

Information which is more deeply processed tends to be remembered better, known as levels of processing theory. This deeper processing refers to considering the information, and reflecting or analyzing how it may fit in with other memories and experiences. This is something that I've tried to naturally incorporate throughout this text.

Rather than simply listing terms and definitions, I've tried to connect ideas and explain why particular concepts are so important. This technique is strengthened when information can be made more personal. This is known as the self-referential effect. Connecting something to your own personal sense of self strengthens your ability to recall it. For instance, if you were trying to remember a random list of words and one was chihuahua, and you have many fond memories with your pet chihuahua, chances are good that you would remember this word better than the others on the list. Thinking of ways you've personally experienced classical conditioning, vicarious reinforcement, or memory failures will strengthen your ability to recall and apply these concepts.

Retrieval cues are related memories that can help us to retrieve a particular memory. You probably use these quite often when you are having trouble recalling something. Imagine that someone has asked you the name of an actor who starred in a particular movie. You know the actor, but you're experiencing blocking and can't come up with his name. You may begin searching your memory for retrieval cues such as other movies that he has starred in. These other movie titles, though they don't feature the actor's name, can serve as retrieval cues because they may be mentally connected to the actor's name. Our related memories tend to form networks of connections to one another, so recalling one can help to activate another.

Similarly, I might ask you to read the following list:

hospital, nurse, sick, bed, stethoscope, physician, medicine, exam, gown

Now if tomorrow I were to ask you to recall as many words from the list as possible, there's a high likelihood that you would recall the word “doctor”, even though it wasn't on the list. Because I activated many words related to “doctor”, it may feel as if doctor itself was activated. This spreading activation of memory can be used to our advantage by activating as many related memories as possible for something that we want to recall. While in the case above recalling “doctor” would be an error, if we really wanted to recall the word doctor tomorrow then reading this list would be an excellent way to help make that happen.

As we'll see in chapter 8, there is a strong relationship between sleep and memory. Sleep seems to play a key role in consolidating our memories while sleep deprivation has clearly been shown to wreak havoc on our ability to form new memories. We'll look at some of the evidence in chapter 8, but for now, suffice to say that getting enough sleep is fundamental to maximizing your memory powers. Long, late nights of cramming might not be nearly as effective as shorter sessions followed by plenty of sleeping time.

This technique is perhaps the most important concept in this book and it has the potential to truly transform your ability to remember. The beauty of this mnemonic technique is that it is incredibly simple and requires only minimal preparation to implement.

The method of locimethod of lociA memory technique that associates items to be remembered with specific locations along a familiar mental route. (sometimes called the Journey Method, or the Roman Room method) has been used for thousands of years and consists of mentally traveling along a familiar route and placing mental images at different locations (loci in Latin) as you go. These mental images represent the information to be remembered, and by using a familiar route, the order of the information will naturally be preserved.

This technique can truly revolutionize your memory abilities. While entire books have been written on the subject of memory improvement, I believe that the method of loci is the most efficient and practical technique that can be taught, and it can be learned in minutes. Of course, practice is necessary to really unlock the potential power of this technique.

First, you need a journey that you know well, such as your home or apartment. Now, let's say that you wanted to remember the 12 animals of the Chinese zodiac, in order. They are:

Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig

In order to quickly memorize this list, you could use your home or apartment and come up with 12 locations (in order) to place each animal. Perhaps you start at your bed, imagining it covered with rats (certainly a memorable, if unpleasant, image), then you'd move to the next location, perhaps a table next to your bed. Imagine a giant ox carefully balanced on the table, trying not to fall off and wake you. Then perhaps you move to the closet where you part the clothes to find a tiger staring you in the face, ready to pounce. As you continue through the natural sequence of your home, you use your imagination to create vivid images.

When you've finished, you'll find that simply mentally traveling through your house will bring each animal to mind. It won't feel like you're “studying” the list at all, but you'll be able to bring it to mind nearly effortlessly. The order of the list will naturally be preserved because the order of rooms won't suddenly change. Now the only limit to how many items you can recall is how many locations your journey has (and how much time you want to spend creating images). This method has been used by world champion memorizers to recall tens of thousands of items.

If you want to remember something permanently you'll still need to review it, and this means you give it a dedicated journey that isn't used for anything else. So if I had 20 products I want to always have mentally ready for work, I might use 20 locations around my workplace for those items and those items only. Then I could effortlessly rattle off all 20 products in order without worrying about leaving any out.

For other information that you only need to remember for a short time, you can use a journey, then reuse that journey later for new information. This multi-purpose journey is like a mental USB drive that you might keep documents on for short periods, constantly swapping things in and out. Just mentally clearing out a journey (by imagining the locations empty) is generally enough to allow you to refill it with new images.

I personally use my childhood home frequently for information that I want to remember short-term but don't need long-term. I use this journey to do memory demonstrations in my classes, in which case I may only need to remember the information (such as a random list of words) for an hour or so. After the demonstration is over and I don't need to remember the info, I simply don't review it. Next time I do a demonstration, I can use the same journey locations again because the old associations have faded.

I believe that when used effectively, the method of loci can incorporate many mnemonic techniques in one and this is what gives it tremendous power. I'd like to briefly outline how all the factors we've learned already can apply to the Method of Loci and why it's the first mnemonic technique I'd recommend to anyone looking to improve memory.

Creating a journey immediately imposes a structure (organizational encoding) and it relies on mental images (known as visual imagery encoding). The Method of Loci forces you to consider the information and connect it to something that you already know (in this case, a familiar journey). This means that you are processing the information more deeply, and this in itself should help to make it more memorable (levels of processing theory). You can add to this effect by considering any emotional response for the image you have created. What other senses and emotions does it evoke (state-dependent memory)? Regardless of emotional impact, the images and relationships you create will be personal (self-referential effect). Even when we struggle to recall something in a journey, the location serves as a vivid starting point to help us (retrieval cue). In addition, this method allows us to review materially mentally by going through our journey so we can review often (spaced repetition) and each time we mentally reach a location and try to recall the image we are testing ourselves (the testing effect).

All of these factors have me convinced that the Method of Loci is the most versatile and effective mnemonic tool for improving memory. But you may not be convinced just yet.

What about things that aren't easily visualized?

This might appear to be the Achilles' Heel for this technique, but fortunately it is a weakness that can be overcome. When faced with items that are hard to visualize (like foreign words, numbers, or abstract ideas) we need to apply additional systems in order to place mental images along our journey. This isn't as hard as it might seem, though creating images will require some creativity.

Sound-alikes - This is sometimes referred to as the Link Method or the Keyword method and it's useful for things that don't have mental images associated with them, such as the sounds of a foreign word. In this case, a mental image is created based on similar sounds that will help link the original word with its definition. For example, if you were learning that the Spanish word for beer is cerveza, you might realize that cerveza sounds a bit like “survey sir” (not exactly, but close enough to cue your memory). You might imagine someone sitting in a bar, and rather than bringing a nice cold beer, the waiter brings a survey to complete, saying “survey, sir”. This mental image might be just enough to remind you that the word for beer is cerveza.

While this technique isn't going to work for every new word you encounter, it can help if you've got a lot of terms to learn. You may even find that just trying to create the sound-alikes will force you to engage with the words and consider self-referential images for remembering them, which certainly won't hurt your chances of correct recall. While this method is often touted as a stand-alone technique, I find it combines quite well with the method of loci because placing the images you create along a journey will help to ensure that you review them and will also provide additional structure to help you retrieve them.

One way to visualize numbers is to use a shape system that creates a visual image for each digit. 0 could be an egg, 1 a baseball bat, 2 a swan, 3 a pair of breasts(!), 4 a sailboat, 5 a hook, 6 a golf club, 7 an axe, 8 a snowman, and 9 a balloon on a string. Now, rather than trying to remember whether a digit was a 4 or a 5, you'll have very different mental images that are less likely to be confused. When confronted with the task of remembering a number you can place a mental image of each digit along a mental journey, just as you did for the animals in the zodiac. Then when you recall the images, just translate back into numbers.

If there were a number that I wanted to permanently commit to memory, I would give it its own journey which is not used for any other information. I've memorized my passport number by using a journey through an airport security check, placing images in the little plastic bin, the x-ray machine, the metal detector, the “wand area”, the end of the conveyor belt, etc. For memorizing a friend's telephone number, you might use their apartment as the journey for the images.

If you're more ambitious, you can try tackling a more complex number system, creating a mental image for every two-digit number. So you'll have a visual image you can bring to mind for all numbers from 00 to 99. This cuts the number of images that you need in half (though it does take a little more time to create and practice with) and adds the advantage of chunking, allowing you to remember numbers in groups rather than single digits. This is a system that I use to memorize numbers and I have a “character” that I bring to mind for each pair of digits. Rather than randomly selecting a person for each number, I populated my list by using a system of name initials shown below.

0=O 1=A 2=B 3=C 4=D 5=E 6=S 7=G 8=H 9=N

This is known as the Dominic System, after Dominic O'Brien, world memory champion and author of several excellent books on memory training. I first learned this system many years ago from one of O'Brien's books on mnemonic systems and methods for memorizing numbers, cards, dates, and more.

So in my list, each two-digit number becomes a set of initials, which then becomes a visual image of a person. If I wanted to recall 341630, the number 34 (CD) becomes Cameron Diaz. 16 (AS) becomes Arnold Schwarzenegger, while 30 (CO) calls up an image of Conan O'Brien. Now when faced with the task of memorizing a long string of digits, I just need to convert each pair to a person and place it along my mental journey. When faced with an odd number of digits, I combine this pair-system with the shape system above, which is only used for the final (single) digit.

If you want to really get extreme, you can also add an action for each character, and then an object as well, so that now each single mental image can store 6 digits (first two digits – person, next two digits – action of second person, next two digits – associated object of third person). So 341630 would become a single image of Cameron Diaz (person), flexing her muscles (action for Arnold), while holding an Eisenhower coffee mug (object for Conan).

This advanced person-action-object technique is mostly for the hardcore mnemonists looking to compete, but it can be used by anyone who has reason or inclination to memorize long strings of digits on a regular basis. The people, actions, and objects are highly personal, and as a result, the above may not make much sense to anyone but me so the biggest time commitment comes in creating your own personalized people, actions, and objects.

Even if you aren't looking to get this deep into the bizarre world of mnemonic techniques, I encourage you to learn the basics of the Method of Loci and apply it whenever you need to memorize something. You might be surprised at just how well your memory works.

Let's end with a more practical example and say that you wanted to memorize Schacter's Seven Sins of Memory from earlier in this chapter. All you would need to do is create a mental image for each sin, then place each image along a 7-location journey. Here's some ideas for visual images for each: Transience (a transient hobo), Absentmindedness (Fred McMurray as the absent-minded professor – or Robin Williams in the remake Flubber), Blocking (a large block of wood), Misattribution (a blurry-faced mugshot), Suggestibility (a smashed-up car from Loftus and Palmer's study), Bias (a scale of justice heavily tipped to one side), and Persistence (a melting watch from Salvador Dali's The Persistence of Memory). It takes a bit of work and imagination to create these images, but once you have done it the time you'll save on mindless studying will be more than worth it.

Now if you placed these images along a short journey, you could review these seven sins any time you wanted, without needing to carry around flashcards or a bulky textbook. With enough practice, eventually you'd easily recall them without even needing to think of the journey at all.