What Babies Pay Attention To

The world is a busy place, and there is much for an infant to learn. The typical infant, when carried around town by her parent, when she is not asleep is fixating curiously and intently on the world around her.

Of course, there are a lot of things in the world that are relevant and worth knowing about, and many which are probably not worth paying too much attention to. Since the baby has so much learn, it would be ideal if children had some mechanism for knowing what they should learn and what they can safely ignore.

The Pedagogical Learning Stance

Gergely Csibra and Gyorgy Gergely have argued that specific social cues are used by caregivers to direct infants to those things most worth learning about. They refer to this as a form of "pedagogy," but my sense is that they don't mean something much like formal education -- these cues can be exchanged without the adult necessarily being aware of them.

Their theory has drawn more attention to the ways in which adults and infants communicate, and what they communicate about. In a recent paper published in Science Magazine, Csibra, Gergely and colleagues suggest that they have found a partial solution to an old riddle in human development.

Perseveration

Perserverance -- sticking to your goals -- is often an admirable quality. Perseveration -- fixating on the same thing long after it ceases to be relevant or useful -- is not.

Babies are known to perseverate. In one particularly classic experiment, Piaget found a strange perseveration in infant behavior. The experiment is easy to replicate at home and works like this:

Put a ball in a bucket such that the infant cannot see into the bucket. Let the infant retrieve the ball from the bucket. Repeat this several times.

Now, in full view of the child, put the ball in a different bucket. Despite the fact that the infant just saw the ball go into the second bucket -- and despite the fact that infants are very good at tracking hidden objects and remembering where they are (contrary to earlier believe, infants ahve no problems with basic object permanence) -- they will typically look for the ball in the first bucket (81% of the time in the current study).

Are babies just stupid?

This failure on the part of the infants to carry out this simple task has often been described as a failure of inhibition. The babies remember that a particular action (searching in the first bucket) has typically led to a positive reward (a ball to play with). Even though they have information suggesting that this won't work this time around, they have difficulty inhibiting what is now an almost instinctual behavior.

What the new study shows is that a fair portion of this is due to the way the experimenter behaves during the experiment. If the experimenter actively engages the baby's attention during the task, the babies show the typical effect of continuing to search in Bucket 1 even when they saw the ball go into Bucket 2.

However, if the experimenter does not directly engage the baby (looking off to the side, not speaking to the baby, etc.), the baby actually does much better (fewer than 50% look in the wrong bucket, down from about 80%). The authors argue that this shows the perseveration effect can't be due to simply motor priming.

They suggest, instead, that by socially interacting with the baby, the experimenter is suggesting to the baby that there is something to be learned here: namely, that a ball can always be found in Bucket 1. When the experimenter does not socially engage the baby, the baby has no reason to make that inference.

Limitations

One might suggest that the babies in the non-social condition were less likely to perseverate because they were less interested in the game and just didn't learn the connection between the ball and Bucket 1 as well.

This is to some extent what the authors are also suggesting. It's important to point out that if the perseveration were caused by priming, attention does not appear to be particularly important to the phenomenon of priming in that you can be primed by something you aren't even aware of (subliminal priming). Still, one could imagine some other mechanism beyond infants believing the adult in the social condition wanted them to learn an association between the ball and Bucket 1.

Also, it is important to note that even in the non-social condition, nearly half of the infants perseverated anyway.

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J. Topal, G. Gergely, A. Miklosi, A. Erdohegyi, G. Csibra (2008). Infants' Perseverative Search Errors Are Induced by Pragmatic Misinterpretation Science, 321 (5897), 1831-1834 DOI: 10.1126/science.1161437

Knowing the meanings of words

In “On the evolution of human motivation: the role of social prosthetic systems,” Stephen Kosslyn makes a very interesting conjecture about social interactions. He argues that, for a given person, “other people serve as prosthetic devices, filling in for lacks in an individual’s cognitive or emotional abilities.” This part seems hard to argue with. Intuitively, we all rely on other people to do certain things for us (mow our grass, edit our papers, provide us with love). His crucial insight is that “the ‘self’ becomes distributed over other people who function as long-term social prosthetic systems.”

You may or may not agree with that stronger claim. I haven't made up my own mind yet. I recommend reading the paper itself, which unfortunately is not available on his website but should be available in a decent college library.

There is one interesting application of his idea to an old problem in linguistics and philosophy.
What is the problem? Intuitively, we would like to believe that our words pick out things in the world (although words and concepts are not interchangeable, for the purposes of this discussion, they have the same problems). When I say “cows produce milk,” I like to believe that this sentence is either true or false in the world. For this to even be plausible, we have to assume that the words “cow” and “milk” refer to sets of real, physical objects.

This is problematic in myriads of ways. It is so full of paradoxes that Chomsky has tried to define away the problem by denying that words refer to anything in the world. I will focus on one particular problem that is relevant to the Kosslyn conjecture.

If you are like me, you know nothing about rare plants such as the three-seeded mercury or the Nova Scotia false-foxglove. Yet, we are able to have conversations about them. I can tell you that the both are endangered in the state of Maine, for instance. If I tell you that they both survive on pure Boron, you would probably be skeptical. Thus, we can talk about these plants and make empirical claims about them and learn new things about them without having any idea what these words actually pick out in the world. This is true of a large number of things we talk about on a daily basis. We talk about people we have never met and places we have never been.

What distinguishes these words from words that truly have no reference? To you, likely neither the words “Thistlewart” nor the word “Moonwart” mean anything. Now, suppose I tell you the first is a made-up plant, while the second is a real plant. To you, these are still both essentially empty words, except one refers to something in the world (though you don’t know what) and the other doesn’t.

Intuitively, what makes “Thistlewart” an empty concept and “Moonwart” not is that you believe there is some expert who really does know what a Moonwart is and could pick one out of a lineup. This “Expert Principle” has seemed unsatisfying to many philosophers, but within the context of the “social prosthetic system” theory, it seems quite at home. Certainly, it seems like it might at least inform some of these classic problems of reference and meaning.

How do children learn to count? Part 3

Two posts ago, I presented some rather odd data about the developmental trajectory of counting. It turns out children learn the meanings of number words in a rather odd fashion. In my last post, I described the "number" systems that are in place in animals and in infants before they learn to count. Today, I'll try to piece all this together to explain how children come to learn to be able to count.

Children first learn to map number words onto a more basic numerical system. They learn that "one" maps on to keeping track of a single object. After a while, they learn "two" maps onto keeping track of one object plus another object. Then they learn that "three" maps onto keeping track of one object plus another object plus another object. All this follows from the Wynn experiments I discussed two posts ago.

Up to this point, they've been learning the meanings of these words independently, but around this time they notice a pattern. They know a list of words ("one, two, three, four") and that this list always goes in the same order. They also notice that "two" means one more object than "one," and that "three" means one more object than "two." They put two and two together and figure out that "four" must mean one more object than "three," even though their memory systems at that age don't necessarily allow them to pay attention to four objects simultaneously. Having made this connection, figuring out "five," "six," etc., comes naturally.

So what is that more basic number system? One possibility is that children to learn to map the early number words onto the analog number system I also described in the last post (the system adults use to estimate number when we don't have time to count)?

Something like this claim has been made by a number of well-known researchers (Dehaene, Gallistel, Gelman and Wynn, to name a few). There are a number of a priori reasons Susan Carey of Harvard thinks this won't work, but even more important is the data.

As I described two posts ago, very young children can hand you one marble when asked, but hand you random numbers of marbles if asked for "two," "three" or any larger number. They always give you more than one, but they can't distinguish between the other numbers. Following Wynn, these are called "one-knowers." Slightly older children are "two-knowers," who can give you one or two marbles, but give you random amounts greater than 2 if asked for another other number. At the next stage, the child becomes a "three-knower." Usually, the next stage is being able to succeed on any number. I'll call those "counters."

Recently, LeCorre and Carey replicated this trajectory using cards with circles on them. They presented the children a card with some number of circles (1 to 8) and asked the kid, "How many?" One-knowers tended to reply "one" to a card with one circle, and then guessed incorrectly for just about everything else. Two-knowers could count one or two circles, but guessed incorrectly for all the other cards. Three-knowers could count up to three, but just guessed beyond that. Counters answered correctly on essentially all cards.

So far this doesn't tell us whether children learn to count by bootstrapping off of analog magnitudes or some other system. Carey and Mathieu LeCorre published a paper this year that seems to settle the question. The setup was exactly the same as in the last paper (now with cards with anywhere from 1 to 10 circles), except that this time the children were only briefly shown the card. They didn't have enough time to actually count "one, two, three..." The data for one-, two- and three-knowers didn't change, which isn't surprising. Both the "3-object" and the analog magnitude systems are very fast and shouldn't require explicit counting.

However, counters fell into two groups. One group, about 4.5 years old on average, answered just as adults. When they saw six circles, their answers averaged around "six." When they saw ten circles, their answers averaged around "ten." This is what you'd expect if they have mapped number words onto the analog magnitude system.

However, the other group, which was slightly younger (average age of 4 years, 1 month), guessed randomly for cards with 5 or more circles, just as if they didn't know how to count. However, these kids can count. If given time to look at the cards, they would have said the right number. So despite the fact that they can count, they do not seem to have their analog magnitude system mapped onto number words.

This means that the analog magnitude system isn't fundamental in learning how to count, and it actually takes some time for children to learn that mapping even after they've learned to count. Carey takes this as meaning that the analog magnitude system doesn't play a fundamental role in learning to count, either, and there are other reasons as well that this is probably the case.

One remaining possibility is that children use the "3-object system" to understanding the meanings of 1, 2 and 3. This seems to work nicely, given that the limits of the system (3 objects in children, 4 in adults) seem to explain why children can learn "one," "two," and "three" without really learning to count. Carey actually has a somewhat more nuanced explanation where children learn the meanings of "one," "two," and "three" the same may that quantifiers (like "a" in English) are learned. However, to the best of my knowledge, she doesn't have an account of how such quantifiers are learned, and if she had an account, I suspect it would itself hinge off of the 3-object system, anyway.

That's it for how children learn to count, unless I get enough comments asking for more details on any point. For those who want to read more, there are many papers on this subject at Carey's web page.

How do children learn to count? Part 2

In my last post, I showed that children learn the meaning of number words in a peculiar but systematic fashion. Today, I'll continue trying to explain this odd behavior.

Important to this story is that children (and non-human primates) are born with several primitive but useful numerical systems that are quite different from the natural number system (1, 2, 3, ...). They can't use these systems to count, but they may be useful in learning to count. In this post, I'll try to give a quick summary of how they work.

One is a basic system that can track about 3-4 objects at a time. This isn't a number system per se, just an ability to pay attention to a limited and discrete number of things, and it may or may not be related to similar limits in visual short-term memory.

You can see this in action by playing the following game with a baby under the age of 2. Show the baby two small boxes. Put a single graham cracker into one of the boxes. Then put, one at a time, two graham crackers into the other box. Assuming your baby likes graham crackers, she'll crawl to the box with two graham crackers. Interestingly, this won't work if you put two graham crackers in one box and four in the other. Then, the baby chooses between the boxes randomly. This is understood to happen because the need to represent 6 different objects all in memory simultaneously overloads the poor baby's brain, and she just loses track. (If you want to experience something similar, try to find a "multiple object tracking" demo with 5 or more objects. I wasn't able to find one, but you can try this series of demos to get a similar experience.)

On the other hand, there is the analog magnitude system. Infants and non-human animals have an ability to tell when there are "more" objects. This isn't exact. They can't tell 11 objects from 12. But they can handle ratios like 1:2. (The exact ratio depends on the animal and also where it is in maturity. We can distinguish smaller ratios than infants can.)

You can see this by using something similar to the graham cracker experiment. Infants like novelty. If you show them 2 balls, then 2 balls again, then 2 balls again, they will get bored. Then show them 4 balls. They suddenly get more interested and look longer. However, this won't happen if you show them 4 balls over and over, then show them 5. That ratio is too similar. (I'm not sure if you get this effect in the graham cracker experiment. I suspect you do, but I couldn't find a reference off-hand. The graham cracker experiment is more challenging for infants, so it's possible the results might be somewhat different.)

You can also try this with adults. Show them a picture with 20 balls, and ask them how many there are. Don't give them time to count. The answer will average around 20, but with a good deal of variation. They may say 18, 19, 21, 22, etc. If you give the adult enough time to count, they will almost certainly say "20."

Those are the two important prelinguistic "number" systems. In my next post, I'll try to piece all this information together.

How do children learn to count? Part 1

How do children learn to count? You could imagine that numbers are words, and children learn them like any other word. (Actually, this wouldn't help much, since we still don't really understand how children learn words, but it would neatly deflect the question.) However, it turns out that children learn to count in a bizarre fashion quite unlike how they learn about other words.

If you have a baby and a few years to spend, you can try this experiment at home. Every day, show you baby a bowl of marbles and ask her to give you one. Wait until your baby can do this. This actually takes some time, during which you'll either get nothing or maybe a handful of marbles.

Then, one day, between 24 and 30 months of age, your toddler will hand you a single marble. But ask for 2 marbles or 3 marbles, etc., your toddler will give you a handful. The number of marbles won't be systematically larger if you ask for 10 than if you ask for 2. This is particularly odd, because because by this age the child typically can recite the count list ("one, two, three, four...").

Keep trying this, and within 6-9 months, the child will start giving you 2 marbles when asked for, but still give a random handful when asked for 3 or 4 or 5, etc. Wait a bit longer, and the child will manage to give you 1, 2 or 3 when asked, but still fail for numbers greater than 3.

This doesn't continue forever, though. At around 3 years old, children suddenly are able to succeed when asked for any set of numbers. They can truly count. (This is work done by Karen Wynn some years ago, who is now a professor of psychology at Yale University.)


Of course, this is just a description of what children do. What causes this strange pattern of behavior? We seem to be, as a field, homing in on the answer, and in my next post I'll describe some new research that sheds light onto the question.

Having solved the question of monkeys & humans, I move on to children and adults

Newborns are incredibly smart. They appear to either be born into the world knowing many different things (the difference between Dutch and Japanese, for instance), or they learn them in a blink of an eye. On the other hand, toddlers are blindingly stupid. Unlike infants, toddlers don't know that a ball can't roll through a solid wall. What is going on?

First, the evidence. Construct a ramp. Let a ball roll down the ramp until it hits a barrier (like a small wall). The ball will probably bounce a little and rest in front of the wall. Now let an infant watch this demonstration, but with a screen blocking the infant's view of the area around the barrier. That is, the infant sees the ball roll down a ramp and go behind a screen but not come out the other side. The infant can also see that there is barrier behind the screen. If you then lift the screen and show the ball resting beyond the barrier -- implying that the ball went through the solid barrier, the infant acts startled (specifically, the infant will look longer than if the ball was resting in front of the barrier as it should be).

Now, do a similar experiment with a toddler. The main difference is there are doors in the screen, one before the barrier and one after. The toddler watches the ball roll down the ramp, and their task is to open the correct door to pull out the ball. Toddlers cannot do this. They seem to guess randomly.

Here is another odd example. It's been known for many decades that three-year-olds do not understand false beliefs. One version of the task looks something like this. There are two boxes, one red and one green. They watch Elmo hide some candy in the red box and then leave. Cookie Monster comes by and takes the candy and moves it from the red box to the green box. Then Elmo returns. "Where," you ask the child, "is Elmo going to look for his candy?"

"In the green box," the child will reply. This has been taken as evidence that young children don't yet understand that other people have beliefs that can contradict reality. (Here's a related, more recent finding.)

However, Kristine Onishi and Renee Baillargeon showed in 2005 that 15-month-old infants can predict where Elmo will look, but instead of a verbal or pointing task, they just measured infant surprise (again, in terms of looking time). (Strictly speaking, they did not use "Elmo," but this isn't a major point.)

So why do infants succeed at these tasks -- and many others -- when you measure where they look, while toddlers are unable to perform verbal and pointing tasks that rely on the very same information?

One possibility is that toddlers lose an ability that they had as infants, though this seems bizarre and unlikely.

Another possibility I've heard is that the verbal and pointing tasks put greater demands on memory, executive functioning and other "difficult" processes that aren't required in the infant tasks. One piece of evidence is that the toddlers fail on the ball task described above even if you let them watch the ball go down the ramp, hit the wall and stop and then lower the curtain with two doors and make them "guess" which door the ball is behind.

A third possibility is something very similar to Marc Hauser's proposal for non-human primate thought. Children are born with many different cognitive systems, but only during development do they begin to link up, allowing the child to use information from one system in another system. This makes some intuitive sense, since we all know that even as adults, we can't always use all the information we have available. For instance, you may know perfectly well that if you don't put your keys in the same place every day, you won't be able to find them, put you still lose your keys anyway. Or you may know how to act at that fancy reception, but still goof up and make a fool of yourself.

Of course, as you can see from my examples, this last hypothesis may be hard to distinguish from the memory hypothesis. Thoughts?