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  • Professor Paul Bloom: I'll begin the class officially

  • with a different sort of demonstration.

  • I want to just show you one of the change-blindness studies

  • that has been done in the real world.

  • And these videotapes are not available publicly.

  • We get them from the web and see them as little Java scripts.

  • So, this is one of the first studies done by Dan Simons when

  • he was at Cornell. And his adviser at the time was

  • our Frank Keil, who's now in our department.

  • So, here's the study.

  • [laughter] And you don't notice it.

  • Change blindness is one of the more striking phenomena

  • discovered by laboratory scientists and by psychologists.

  • But it's important to realize, to get away from the sort of

  • surprise of the gorilla and the fact that it's hard to see the

  • flickering--the object that's flickering,

  • and appreciate the big moral of this, because the big moral of

  • this is actually, I think, striking and quite

  • important. You think right now that you're

  • perceiving the world. I look down on you and I think

  • I have a whole sense of where everybody is.

  • I can't see everybody perfectly in back.

  • You're kind of far away and blurry but there's a sense in

  • which I have a world around me. Similarly, if I'm to close my

  • eyes for a second, everything just remains and I

  • could sort of remember some of the things that are there.

  • That's really good sound localization by me .

  • So you're looking up and you think you have a sense of the

  • world both in perception and memory.

  • The change-blindness experiment suggested this isn't true.

  • The change-blindness experiment suggests that if you look at me

  • for a second and during that second all of your classmates

  • change positions, including those next to you,

  • you are extremely unlikely to notice.

  • The change-blindness experiment suggests that if you turn your

  • eyes away from me towards there for a second and turn back,

  • and I'm dressed entirely differently, you wouldn't

  • notice. The exceptions would be if you

  • told yourself consciously, "Remember what this guy is

  • wearing; he's wearing this,

  • that and the other." But if you don't do it

  • consciously you'll lose it, and usually this is okay.

  • Usually, it's okay because your memory and your visual system

  • exploits a basic fact about the universe,

  • which is that most things stay the same most of the time.

  • I don't have to explicitly remember that you're over there

  • when I turn my head for a second because you'll be over there in

  • any case. You don't need to hold precise

  • representations of the world. And so you only notice it in

  • certain clever circumstances. One sort of clever circumstance

  • is when psychologists change reality as in the

  • change-blindness studies. A second sort of circumstance

  • is in movies. So, one of the big surprises

  • when people started making movies involving cuts was it is

  • extremely difficult to get everything continuously right.

  • And you need to work very hard to notice.

  • So, there's all of these continuity errors that creep up

  • into movies and you have to be a film buff or writing it down to

  • even notice this. And the overall moral here then

  • is that your perception of reality is a lot more sparse,

  • a lot more limited, than you might think it is.

  • So, this is where we were at the end of last class.

  • We were talking about the different sorts of memories:

  • Sensory memory, which is the sort of fraction

  • of a second of sensory residue of what you're hearing and what

  • you're seeing, working memory,

  • short-term memory, and then long-term memory.

  • And we talked last class about how things get into sensory

  • memory, into working memory, the role of attention.

  • And in fact, the change-blindness studies

  • are actually just studies of how something gets from your senses

  • to your consciousness and what does and what doesn't.

  • Now I want to move to the distinction between working

  • memory, short-term memory, and long-term memory.

  • Now, the obvious distinction is actually just in fact--is

  • storage differences. So, long-term memory or "LTM"

  • has a huge storage capacity. This is your memory like the

  • hard drive of your computer. This is the memory you walk

  • around with. It includes all the words in

  • English, just for example, 60 to 80,000 words.

  • It includes everybody you've ever met, languages,

  • faces, stories, locations, nursery rhymes,

  • songs, TV programs. Nobody knows the storage.

  • It is not true that you remember everything that has

  • ever happened to you. There's no reason to believe

  • that this is true. At the same time though,

  • you have a huge amount stored in your brain in long-term

  • storage and nobody actually--It has to be limited because it's a

  • finite, limited brain.

  • But nobody knows how big it is. Nobody knows how many terabytes

  • you carry around in your brain and--but it's a lot.

  • Compare this to working memorythe short-term memory,

  • which is actually very limited. Your memory of what you could

  • store on--in--where you could hold in consciousness right now

  • is quite limited. Here is an exercise.

  • Do not write these things down. I want you to remember them.

  • I'm just going to give you a few numbers: 14,59,

  • 11,109, 43,58, 98,487, 25,389,

  • 54. Please write them down.

  • View this as an IQ test if that would relax you.

  • How many of you who decided to participate in this experiment

  • got three or less? Good.

  • Good. Four, five, six,

  • seven, eight, nine or more?

  • Anybody get all eleven? This is a particularly

  • difficult memory task. The numbers are meaningless.

  • And I told--and I forgot to tell you to get your pen and

  • pencil ready, so some of you just glared at

  • me. But [laughter]

  • under normal circumstances the cognitive psychologist George

  • Miller said that this sort of suggested that the standard

  • memory storage of short-term memory is seven,

  • plus or minus two. And what that means is anywhere

  • from five to nine roughly. Some of you,

  • I bet, can beat that. Some of you on a not-so-good

  • day maybe won't make it that much.

  • Now "seven plus or minus two" is what you--;so,

  • that's what you hold in consciousness.

  • I can tell you 14,21. You walk around,

  • "Oh, yeah, 14,21." You hold that in consciousness

  • with no problem. But I throw eleven numbers at

  • you, you can't. Some dribble out.

  • You can't hold that in your conscious window in your

  • short-term memory. Now, this raises the question

  • "seven plus or minus two" what? And the answer seems to be what

  • George Miller calls "chunks." And a chunk is a basic memory

  • unit, something you think of as a single, individual entity.

  • So, suppose you see the string of letters "L,

  • A, M, A, I, S, O, N."

  • If you don't know--If you can't form these into words and you

  • have to remember them, these are eight chunks.

  • You have to just pick them up separately.

  • On the other hand, if you break them up into four

  • words you could just remember it as four chunks.

  • And if you break it up into two words in French,

  • "la maison," "the house," it could just be one or two.

  • How much you know depends--affects how much you

  • memorize--how much you could store in memory because it

  • affects what counts as a basic unit of memory.

  • And there's all sorts of examples of this.

  • If I tell you "1,1, 0,1, 1,0, 0,1,

  • 0,1, 1,0," those of you who don't know binary numbers might

  • have to remember that as "1, 1,0, 0," whatever I said.

  • Those of you who are computer scientists or mathematicians or,

  • for whatever reason, know binary numbers could

  • convert it into a single binary number.

  • Anybody know what the number is? No, I cannot say it again.

  • [laughter] Some number,

  • 24, or not 24--to some number, 24, and then you remember "24."

  • It's easier. Suppose you see a chessboard

  • and the chessboard is set up and you don't know how to play

  • chess. It is murderously hard to

  • remember that. They've done the experiments.

  • They've taken people in a lab who don't know how to play

  • chess. They set up a chessboard and

  • then they say, "Okay.

  • Look at this for five minutes." Then they take it away,

  • set it up again, and it's murderously hard.

  • "There is a horse-y thing on the side there and everything."

  • But if these chess pieces are set up in some way that's

  • logical for a chess player, then a chess master could look

  • at it and remember it in a glance, "Oh.

  • It's the Fibonacci defense" or something like that [laughs],

  • and then immediately recover it.

  • Similarly, football coaches have been tested on their

  • memories of football diagrams. And they have a photographic

  • memory for football diagrams because it corresponds to things

  • that make sense. Architects could have a

  • photographic memory, a perfect memory for floor

  • plans because it makes sense to them.

  • They understand it. And so the way you store things

  • in memory, and this is a theme we're going to return to when we

  • get to long-term memory, depends in a large extent on

  • how much you understand it. And this shows up in expertise

  • effects. Now, this is what's happening

  • so far in short-term memory, how much you hold in there.

  • The question is how do you get it into long-term memory?

  • So, you have long-term memory, your major storage system.

  • How does information get from your consciousness to long-term

  • storage? Well, there's one

  • thing--there's one way which sort of works sometimes but not

  • very well. And it's called "maintenance

  • rehearsal." Suppose I said you have to

  • remember this number, this string of numbers.

  • And if you remember it in twenty minutes you will get one

  • thousand dollars. And the string is my phone

  • number when I was a kid. I'll include the area code:

  • 514-688-9057. Now, if you tell that to a

  • four-year-old, well, the four-year-old will

  • say, "I'll remember it." And then you ask them,

  • "What did I just say?" "Well, I don't know."

  • If you tell it to an--because you know something--If a lot

  • depended on it, you would know to do something.

  • What you would do is you'd say to yourself, "514-688-9057,51

  • 4-688-9057,514-688 --" You'd rehearse it in your head over

  • and over again. The problem is you could hold

  • it as long as you can do that. It's like these movies.

  • You see this all the time, like an episode of 24:

  • "Jack, call CTU and tell them Agent 11 is trapped in a--" And

  • I can't even remember this but the way to remember it is you

  • hold--you've just got to repeat it over and over again in your

  • head. But this will not typically get

  • things into long-term memory. To get things into long-term

  • memory, rehearsal is usually not enough.

  • You need to do other things. Typically, what you need is

  • structure and organization. And one way to demonstrate this

  • was in a classic "depth of processing" experiment which

  • nicely illustrates the fact that the more you structure

  • something, the deeper you think about it,

  • the better it gets entrenched in the long-term memory.

  • So, in this study what they did was they asked people--they told

  • people that there's going to be words flashed on a screen.

  • And all of the subjects saw the same strings of words.

  • There were forty-eight words. They were not told to memorize

  • the words. One third of the subjects was

  • told, "Look. Some of these words are going

  • to come out in capital letters, some of them not capital

  • letters. Press a button for capitals,

  • non-capitals." "Sure."

  • The other group was told, "Some of these words will rhyme

  • with 'train,' Others won't. Press a button if it rhymes in

  • 'train'." The third group was told,

  • "Does it fit into the sentenceThe girl placed the blank on

  • the table'? Press a button if it does.

  • Press a button if it doesn't." Then they were asked as a

  • surprise, "What words did you see?"

  • And the findings looked like this.

  • When they were asked to focus on just what the word looked

  • like, memory was very poor, the sound better,

  • the meaning better. If you want to remember

  • something, the best way to remember it is to give it

  • meaning, to give it sense. This is illustrated through a

  • very ancient technique, which is that the way to

  • remember things that are otherwise arbitrary is to give

  • them some organization through memory tricks,

  • through vivid imagery or songs or poetry.

  • And there's a lot of examples of this.

  • Do you know how to remember that the hippocampus--There's a

  • part of the brain called the hippocampus.

  • This is the worst memory trick ever but it will stick with you

  • for twenty years. The hippocampus is involved in

  • spatial memory. It's involved in finding your

  • way around. Think to yourself,

  • "The way I find my way around campus is through the

  • hippocampus." And you think,

  • "Well, that's stupid," but you'll never forget now that the

  • hippocampus is in charge of spatial memory.

  • It's going