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  • It was midnight when Bernice got off work.

  • She was exhausted after a long and terrible day, and just wanted to get home to a hot bath.

  • She was driving down the street, flipping through radio stations, when she pulled up

  • to a stop sign, and saw something weird. A shadowy figure ran up to an idling fruit truck,

  • pushed the delivery man down, grabbed a crate of bananas, and ran off around the corner.

  • Bernice was pretty shaken up,

  • but she made sure the driver was okay, and then called the police, describing the thief as a pale,

  • lanky man, wearing a dark jacket and a baseball cap. She gave the cops her information, and

  • then she went home. A couple days later the police asked her to

  • come down to the station to identify a potential thief--a guy who more or less matched her

  • description, and was found eating a banana early that morning, near the scene of the crime.

  • Although the guy professed innocence,

  • Bernice said it was him, and they locked him up. But at the trial, the defense called a memory

  • expert to the stand, and soon after that, the suspect walked.

  • Today’s lesson may not quite make you an expert worthy of the witness stand, but by

  • the time were done, youll understand a lot more about how we retrieve memories

  • we think weve stored, and why the accused banana thief was set free.

  • [INTRO]

  • Were all constantly retrieving memories throughout the day-- youre remembering

  • where you parked your car, or if you fed the cat, or called your momcause it’s her birthday.

  • Youll remember from last week that while

  • our implicit memories--like how to talk and ride a bike--are dealt with on a mostly automatic

  • and non-conscious level, our explicit memories--the chronicles of our personal experiences and

  • general knowledge -- often require conscious, effortful work.

  • Bernice had to notice, encode, store, and later consciously retrieve details about the

  • crime she witnessed--what color was the guy’s jacket, what did he look like, what did he

  • steal, and where did he run? It takes a lot of work to retrieve memories

  • from long-term storage, and the truth is, a lot can go wrong along the way.

  • In order to understand all of the many fascinating ways you forget things, we need to talk more

  • about how we remember. Our memories are not like books in the library

  • of your mind. You don’t just pluck a neatly-packaged memory -- about where you left your phone

  • or the hair color of a fruit thief. Instead your memories are more like the spider

  • webs in the dank catacombs of your mind--a series of interconnected associations that

  • link all sorts of diverse things, as bits of information get stuck to other bits of

  • information. Like, maybe Bernice remembers that the night

  • of the crime was chilly with a full moon, and that Beyonce was on the radio, and the

  • fruit truck had plates from California, which is where her grandfather lives.

  • All those bits of information in the web of memory--the weather, the song, the plates--can

  • serve as retrieval cues, kind of like a trail of breadcrumbs leading back to a particular

  • memory. The more retrieval cues you inadvertently,

  • or intentionally, build along the way, the better you can backtrack and find the memory

  • youre looking for. This way of activating associations non-consciously

  • is called priming, sometimes calledmemoryless memory”. It’s howinvisible memories

  • that you didn’t know you had can awaken old associations.

  • Priming is how you often jog your memory. This kind of recall is sometimes referred

  • to as context-dependent memory. Say youre reading in bed, and you want

  • to underline a quote, but you don’t have a pen. You get up and go into the other room

  • to find your special light-up Hello Kitty pen, but you get distracted and suddenly you

  • find yourself in the kitchen; youre likeWhy? Why, mind? Why am I in the kitchen?

  • What is here? Why am- there was a rea- and I don’t know but I’m here now and agh!”

  • It’s only when you retrace your steps and return to bed, to the initial context where

  • you read that quote and encoded that first thought of wanting that pen, that the memory

  • comes back. And then youre likeoh, I need to go get the pen. Ugh

  • If some memories are context-dependent, others are state-dependent, and also mood-congruent.

  • This just means that our states and our emotions can also serve as retrieval cues.

  • If I had a throbbing headache and a super bad day, I’m more likely to start recalling

  • bad memories, because I’m priming negative associations. But of course if I’m relaxed

  • and jolly, I’m prone to remember happy times, which are prolonging my good mood.

  • Another funny memory-retrieval quirk speaks not to our location or emotions, but to the

  • order in which we receive new information. So, say you make a grocery list in the morning,

  • but a few hours later, youre at the store, you realize you left it at home.

  • You’d be more likely to recall the first items on the list--bananas and bread--and

  • the last items--pickles and cheese--than anything in the middle. This is known as the serial

  • position effect. This might be because the early words benefitted from what’s known

  • as the primacy effect, and made it into your long-term memory because they were rehearsed

  • more. Meanwhile, the last words lingered in the working memory through the recency effect.

  • But those poor middle words, they didn’t benefit from either effect and therefore escaped

  • your brain, which is why you now have no toilet paper, dog food, toothpaste, or cookies. Who

  • forgets cookies? But even with all these tricks and associations,

  • things still go wrong--memory can fail or become distorted, and of course we forget

  • things. Forgetfulness can be as minor as those frustrating

  • moments where youre likeAh, it’s on the tip of my tongue. It’s the guy, the

  • guy’s got hair, and a face, and, like, shoulders.’ Or as major as Clive Wearing, whose neurological

  • damage made it impossible for him to recall the past or create new memories.

  • Of course, we all forget things, and typically we do it in one of three different ways: We

  • fail to encode it, we fail to retrieve it, or we experience what psychologists call storage

  • decay. Sometimes forgetting something just means

  • it never really got through your encoding process in the first place. I mean, think

  • of all the stuff that’s going around you at any given moment. We only actually notice

  • a fraction of what we sense, and we can only consciously hold so many bits of information

  • in our minds at any given time, so what we fail to notice, we tend to not encode, and

  • thus don't remember. Bernice noticed a dark jacket, Beyonce, and

  • bananas, but she didn’t encode much about the driver, or the color of the thief’s

  • shoes. Then again, even memories that have been encoded

  • are still vulnerable to storage decay, or natural forgetting over time.

  • Interestingly, even though we can forget things pretty quickly, the amount of data that we

  • forget can actually levels off after a while. This means that Bernice would have forgotten

  • about half of what she first noticed from the crime scene a couple days later, but what

  • she still remembered, she’d likely hang on to, because the rate at which we forget

  • tends to plateau. A lot of times forgetting doesn’t mean our

  • memory just faded to black, it means we can’t call it up on demand because of retrieval

  • failure. We all know the common tip-of-the-tongue phenomenon

  • where you feel like you know the name of that weird-looking hard-backed animal that rolls

  • up into ball. It’s kind of cute and weird and I think they get leprosy or somethingwhat

  • is it?! This is where retrieval cues can come in handy. If I say is starts with the letter

  • A, you may suddenly unlock the information--Armadillo!

  • Sometimes these retrieval problems stem from interference from other memories getting in

  • the way, essentially cluttering the brain. Sometimes, old stuff that youve learned

  • keeps you from recalling new stuff -- like, if you change one of your passwords, but keep

  • recalling your old one every time you try to log in. That’s called proactive, or forward-acting,

  • interference. The flip side is retroactive, or backward-acting,

  • interference, which happens when new learning gets in the way of recalling old information,

  • like if you start studying Spanish, it may interfere with the French that youve already

  • learned. There’s a lot of reconstruction and inferring

  • involved when you try to flesh out a memory, and every time you replay it in your mind,

  • or relate it to a friend, it changes, just a little. So in a way, were all sort of

  • perpetually re-writing our pasts. While this is an inevitable part of human

  • nature, it can prove dangerous at times. Misleading information can get incorporated

  • into a memory, and twist the truth - and yes there is an effect for this; it’s called

  • the misinformation effect. American psychologist and memory expert Elizabeth

  • Loftus has spent decades showing how eyewitnesses inadvertently tweak and reconstruct their

  • memories after accidents or crimes. In one experiment, two groups watched a film

  • of a car accident. Those asked how fast the cars were going when they smashed into each

  • other estimated much higher speeds than those who were asked about the cars hitting each

  • other. Smash is the leading word that essentially

  • altered the witnessesmemories -- so much so that a week later, when both groups were

  • asked if they saw any broken glass, those who heard the word smash were twice as likely

  • to report seeing bits of glass, when in fact, the original film didn’t show any.

  • In Bernice’s case, chances are her memory of the robbery would be altered if the prosecution

  • said the thief assaulted, rather than pushed the driver.

  • This sort of interfering or misleading information may also manifest itself as source misattribution,

  • like when we forget or misrecall the source of a memory.

  • In the case of Bernice, when she saw the suspect in the courtroom, she thought she recognized

  • him from the night of the crime, when in reality, he’d just served her coffee earlier that

  • day. But her memory of the event had probably already

  • been tweaked several times before she even made it into the courtroom. Like she re-lived

  • the tale multiple times, in her own mind or when she told other people about it, and every

  • time she introduced errors, filling in memory gaps with reasonable guesses.

  • Not only that, but we know Bernice was already tired and stressed when she witnessed the

  • event, and we know our emotions can influence both what we remember and what we forget.

  • Because memory is both a reconstruction and a reproduction of past events, we can’t

  • ever really be sure if a memory is real just because it feels real.

  • Elizabeth Loftus knows this. She’s frequently called in to testify against the accuracy

  • of eyewitnesses. In fact, of all the U.S. prisoners who have been exonerated based on

  • DNA evidence presented by Innocence Project, a non-profit legal group, 75 percent of them

  • were convicted by mistaken eyewitnesses. That is a lot of innocent people.

  • Bernice meant well of course, she’s an honest enough lady, but all these factors--the emotion,

  • the retelling, the suggestions of outside sources-- combined with the darkness, the

  • quick glimpse, the passing of time, maybe even the Beyonce, ended up leading to a mistake

  • in the thief’s identification. Turns out the human memory is actually a very

  • fragile thing. Were all largely the product of the stories that we tell ourselves.

  • If you haven’t forgotten already, today you learned about how our memories are stored

  • in webs of association, aided by retrieval cues and priming, and influenced by context

  • and mood. You also learned how we forget information, how our memories are susceptible to interference

  • and misinformation, and why eyewitnesses are often not as reliable as you might think.

  • Thanks for watching, especially to all of our Subbable subscribers, who make this whole

  • channel possible. To learn how you can keep these lessons coming while earning awesome

  • perks, just go to subbable.com.

  • This episode was written by Kathleen Yale, edited by Blake de Pastino, and our consultant

  • is Dr. Ranjit Bhagwat. Our director and editor is Nicholas Jenkins, the script supervisor

  • is Michael Aranda, who’s also our sound designer, and the graphics team is Thought

  • Café.

It was midnight when Bernice got off work.

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記憶することと忘れること - クラッシュコース心理学 #14 (Remembering and Forgetting - Crash Course Psychology #14)

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    Elma Kung に公開 2021 年 01 月 14 日
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