字幕表 動画を再生する 英語字幕をプリント This episode is supported by The Great Courses Plus. Hi, I’m Thomas Frank, this is Crash Course Study Skills, and if you happen to be watching this at whatever point in the future that we all get neural implants to let us store our memories on servers in space, what I’m about to tell you is woefully inaccurate. Also, do we have flying cars yet? For those of you who still rely on that mushy gray stuff in your cranium to remember things, though, listen up. Today we’re digging into how your memory works and how you can make it work better. At least, I think we are. Nick, we’re not filming those makeup tutorials today, are we? [Theme Music] The science of how memory works is complicated, to say the least. After all, how do we explain how a bunch of nerve cells, chemicals, and electrical jolts somehow let you remember algebra, where you left your car keys, and all the lines to The Dark Knight? Well, it’s simple. We, uh…. rely on Hank from 3 years ago to do it for us. Seriously, there are two whole episodes of Crash Course Psychology that go through the entire process of how memories are formed and retrieved. But just like Xzibit left to his own devices in a car dealership, I can’t resist putting crash courses in your Crash Course. Plus, understanding how your memory works will help you to optimize the way you study. So let’s do a quick review. Your brain turns information into memories by putting it through a few different stages. The first is sensory memory, which processes pretty much everything your senses detect or experience in the real world. That sensory memory has the attention span of a five-year-old at the DMV, though, so most of what it takes in is lost almost immediately. But what does stick moves into your short-term or working memory. This type of memory is sort of like the RAM in your computer – the memories don’t stick around permanently. In fact, unless you continuously rehearse what’s floating around in working memory, it’ll pull a disappearing act after about 15-30 seconds. This can also happen if you try to cram too much in at once, because your working memory can really only handle 4-7 bits or items of information at a time. Now you can somewhat increase this limit by grouping bits into chunks – like splitting “FBIKGBCIA” into FBI, KGB, CIA, but there’s still a limit. Now, all this happens primarily in your brain’s prefrontal cortex, but eventually the information has to make its way to other areas of the brain if it’s going to be encoded in long-term memory. To greatly simplify things, it’ll first head to the hippocampus, which augments it with chemicals called neurotransmitters. Along with many other functions, these transmit details about the information – metadata, if you will. Eventually, this leads to the formation of new synapses, which are essentially connections between neurons – though the neurons don’t actually touch. Instead, they prefer to keep a small gap between each other and let more of those neurotransmitters move information between them. The whole process of memory formation causes physical changes within your brain: neurotransmitters shuttle all over the place, neural pathways are forged, and neurons themselves undergo structural improvements using proteins such as brain-derived neurotrophic factor, or BDNF. And, just like the process of strengthening your muscles through exercise, this all takes time – which is why cramming for a test doesn’t work, and why you can’t instantly just download jujitsu into your brain like Neo. As Pierce J. Howard noted in his book The Owner’s Manual for the Brain: “Work involving higher mental functions, such as analysis and synthesis, needs to be spaced out to allow new neural connections to solidify. New learning drives out old learning when insufficient time intervenes.” Now that you have a bit of an understanding of how your memory works, one crucial tip should be clear: you have to space your learning out over time. But we’re not going to just leave it at that, because – as cognitive scientists have known for a long time – the way you do that spacing matters quite a bit. To explain this, let’s start with why we forget things in the first place. Part of the reason is that your brain doesn’t encode all memories equally. During the long-term encoding process, the hippocampus will use different levels of neurotransmitters based on, among other things, how important the information is. And this plays a big role in how strongly it’s embedded in long-term memory. This filtering mechanism is great for survival, as it allows your brain to safely disregard unimportant things, like what you had for breakfast two weeks ago, while paying special attention to what’s important, like that fact that there are ninjas behind you right now. Unfortunately, you can’t always consciously decide what’s important and what’s not, which is why it can be hard to remember all the details from that history chapter you just read. At a primal level, your brain just doesn’t think the details of Genghis Khan’s war with the Quarismian Shah in 1219 are as important as a bear attacking you. However, there are a few tricks you can pull to make it care a bit more. First, understand that your brain latches more readily onto things that are tangible, visual, and uncommon than it does with the abstract or the mundane. Because of this, it can be helpful to develop mnemonics, which are mental devices that help you associate pieces of information in ways that are easier to remember. And mnemonics can take many forms. You can create sayings to remember sequences of letters – such as “Ernie Ate Dynamite, GoodBye Ernie” to remember the names of the strings on a guitar. Or you can make up weird stories in your head that includes cues to the information you’re trying to associate. Like, the way I remember that Helsinki is the capital of Finland is by imagining a giant flaming sinkhole in the ground opening up with a bunch of sharks jumping out of it. Since it’s weird, it’s easy to remember, and it helps me associate the words Hell, Fin, and Sink, which in turn connect Finland and Helsinki. Additionally, the more connections that lead to a memory, the stronger it’ll be – especially if they’re learned in different contexts. When I first learned about caravels, which were those small ships that Portuguese explorers used to travel down the African coast in the 15th century, I had a hard time remembering that name – caravels. But once I started using them in Civilization V to build my empire – and to make sure Ghandi never got far enough to nuke me, the memory became a lot more solid, since I was interacting with it in a new context. Of course, you still have to repeatedly access your new memories once they’re encoded if you want them to stick around. This is pretty much the iron law of memorization: Except in cases where they’re attached to a particularly intense emotional experience, memories fade away unless you repeatedly recall them. Well, sort of. Let’s go to the Thought Bubble. In the 1880’s, a German psychologist named Herman Ebbinghaus wanted to understand how memories decayed over time, and he especially wanted to know how long the process took. He began by running countless tests on his own memory, forcing himself to recall long lists of meaningless letters until eventually, he came up with the Forgetting Curve. While largely hypothetical and simplistic in its details, this model demonstrated how memories decay quickly unless accessed again and again. Since Ebbinghaus’s days, our understanding of how memory decays has come a long way. According to the Forget-to-Learn theory, which is presented in Benedict Carey’s book How We Learn, memories actually have two different strengths: storage strength and retrieval strength. Picture your brain as a library where none of the books ever get stolen or damaged. When a new book is put on a shelf, it’s there for good. This represents storage strength, which, according to the theory, doesn’t weaken. Once a memory is encoded, the neural pattern can only get stronger. Now, unfortunately this library has a particularly lazy librarian who doesn’t do a very good job of keeping the library’s catalog organized. This represents retrieval strength, which does fade with time. Unless you go in and organize the catalog – or recall the memory – you’ll eventually lose track of it. Thanks, Thought Bubble. Now here’s where it gets good. The more a memory’s retrieval strength has faded, and the greater the difficulty of recalling it, the greater the increase in learning will be. This is called the Spacing Effect. It’s essentially the “No pain, no gain,” of the mental realm; the harder you have to work to recall something, the greater the reward for doing so. There’s an obvious catch, though – if you wait too long, the retrieval strength diminishes so much that you won’t be able to recall the memory at all. This where the Principle of Desirable Difficulty comes in. To maximize the efficiency of your studying, you want to the find the point right before you’re about to forget something. And you can do this by using spaced repetition techniques. The general idea behind spaced repetition is to steadily increase the amount of time in between each study session for any piece of information. So instead of reviewing a fact or concept once every few days, you’d use a schedule like this where you’d wait a day between the first and second sessions, three days between the second and third, and so on. To do this precisely, you need a system that tracks your progress in memorizing each piece of information you need to study – since it never happens evenly. If you’ve got 100 Japanese kanji to learn, it’s inevitable that you’ll remember some easier than others. If you use the exact same time delays for every kanji, you’ll spend too much time studying some, and others won’t ever be learned at all. To solve this problem, you can use the Leitner System. In it, you’ve got five boxes, each of which represents a specific study interval. Box 1 gets studied every day, Box 2 every three days, Box 3 once a week, and so on. Every fact or term gets its own flash card, and all cards start off in Box 1. Once you get a card right, move it to the next box. And if you get a card wrong – no matter what box it’s in – send it back to Box 1. If you play by these rules, you’ll ensure that you maximize your efficiency by spending more time studying the cards you have the weakest grasp on. The increasing time intervals of the boxes also help you leverage the spacing effect and get to close to that point of desirable difficulty. There are also a ton of spaced repetition apps for both computers and smartphones that will let you make this whole process digital. The best known one is probably Anki, which is free on most platforms, but there’s also TinyCards, Quizlet, and many, many others. Now when it comes to subjects that aren’t easily studied through flash cards – like math or even a sport like skateboarding – it’s harder to use a rigid spaced repetition algorithm. However, the spacing effect applies here as well, so be sure to space out your practice over time. During any given day’s practice, you’ll eventually hit a wall where you stop making progress whether it’s learning derivatives in calculus or kickflips in skateboarding – but if you come back to it a few days later, everything will be more likely to click into place. In each of these study sessions, make sure you’re putting the focus on recalling information from your own memory. As we talked about in our video on reading assignments, there are two main kinds of memory – recognition and recall. Recognition is what happens when you’re exposed to information you’ve already seen before and remember it. But recall involves dredging the information up from the depths of your memory banks without seeing it, which is exactly what you’ll have to do in both your exams and in many real-world situations. So when you study, make sure you’re focusing on active recall. Don’t just passively read over your notes or slides – use them to create quizzes for yourself, or challenge yourself to sit down and write out a summary of what you’ve learned from memory. If you’re studying a subject like math or physics, put a huge emphasis on practicing with real problems and actually use the concepts and formulas you’ve learned. In short, studying should feel like work, and it should challenge your brain. When it does, you’ll remember more while spending fewer hours at your desk. Thanks for watching, and I’ll see you next week. This episode is brought to you by The Great Courses Plus, an on-demand subscription service where you can get unlimited access to over 7,000 different video lectures about any topic that interests you, including science, literature, history, math, even cooking or photography. The classes are taught by award winning professors – from the Ivy League and other top schools around the world. If you're looking to improve your study skills further, you might like this lecture from Professor Steve Joordens, called Encoding—Our Gateway into Long-Term Memory where you'll learn more about how to improve your own recall. Right now, The Great Courses Plus is offering Crash Course viewers a free one-month trial. Go to thegreatcoursesplus.com/studyskills, or click on the link in the video description below, to start your free trial today. Crash Course Study Skills is filmed in the Dr. Cheryl C. Kinney Crash Course Studio in Missoula, MT, and it's made with the help of all of these nice people. 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