Learning verbs is hard

I am getting ready to write up some of my recent research on verb learning — a project for which the Dax Study and the Word Sense experiments are both follow-ups. This means a spate of reading. As I come across interesting papers, I’ll be sharing them here.

First, though, I’d like to note that my recent post, “Psychic word learning. No seriously,” for some reason never made it to the main page of this site, and most people missed it. Check it out here.

A PsychInfo search turned up a very intriguing paper by Kerstin Meints, Kim Plunkett and Paul Harris published earlier this year in Language and Cognitive Processes on verb learning.

What is tricky about verbs?

Verbs are very difficult words — both for linguists to describe and for babies to learn. In this post, I’ll focus on the second part.

First, unlike nouns, verbs refer to something you can’t see. You can point to a ball, but it is much harder to point to thinking. Even action verbs (break, jump) are typically used when the action has already been completed and is no longer visible.

To make matters worse, Lera Boroditsky and Deidre Gentner have noted that verbs are more variable across languages than are nouns, which means either that there can be fewer innate constraints in acquisition or that there simply are fewer such constraints.

The tricky aspect of verbs that Meints, Plunkett and Harris focus on, though, is the way in which verbs generalize. For instance, to use the verb eat correctly, you have to use it to describe the actions of many different eaters (horse, cow, Paul, Sally, George) as well as many different objects which are eaten (sandwich, apple, old boot).

Nouns, of course, have to be generalized. Not all apples look the same. But then, neither do all acts of eating (politely, messily, with a fork).

Using a verb to its fullest

Meints, Plunkett & Harris noted that for any given verb, there are stereotypical direct objects (John ate the cookie) and unusual direct objects (John ate the bush).

One might imagine that children start off expecting verbs to apply only to stereotypical events, because that’s what they actually hear their parents talk about (Don’t eat the cookie!). Only later do they learn that the verb extends much more broadly to events which they have never witnessed or discussed (Don’t eat the bush!).

This seems like a very plausible learning story, very similar to Tomasello’s Verb Islands hypothesis, though I’m not sure if it’s one he explicitly endorses (hopefully, I’ll be reading more Tomasello shortly).

Alternatively, children might start by assuming a verb can apply across the board. That is, children treat verbs categorically, more in line with the algebraic theories that most linguists seem to endorse but which a number psychologists find implausible.

The data

The researchers used a tried-and-true method to test the language abilities of young kids: present the kids with two videos side by side (for instance, of John eating a cookie and of Alfred sweeping a floor) and say “look at the eating.” If the child knows what “eating” means, they should look at John and not Alfred.

The key manipulation was that the eating event was either stereotypical (John eating a cookie) or unusual (John eating a bush). Note, of course, that a number of verbs were tested, not just eating.

15 month olds failed at the task. They didn’t appear to know any of the verbs. 18 month olds, however, looked at the correct video regardless of the typicality of the event. They understood verbs to apply across the board. 24 month olds, just slightly older, however, looked at the correct video for the typical event but not for the atypical. By 3 years old, though, the kids were back to looking at the correct event regardless of typicality (though they reportedly giggled at the atypical events).

What does that mean?

The difficulty with cognitive science is not so much in creating experiments, but in interpreting them. This one is difficult to interpret, though potentially very important, which is why I called it “intriguing.”

The results minimally mean that by the time kids can perform this task — look at an event described by a verb when that verb is mentioned — they are not immediately sensitive to the typicality of the event. Later, they become sensitive.

At least two issues constrain interpretation. First, we don’t really know that the 18 month old infants were not sensitive to typicality, only that they didn’t show it in this experiment. Second, we don’t know whether the 24 month olds thought the event of John eating a bush could not be described by the verb eat (which would be wild!) or if they simply found the video such an implausible instance of the verb eat that they paid equal attention to the other video, just in case an a more typical example of eating showed up there.

In conclusion

So which theory of language learning does this result support? I honestly am not sure. If it had shown a growing, expanding interpretation of verb meaning, I might have said it supported something like the Verb Island hypothesis. If children started out with an expansive understanding of the verb and stuck with it, I might say it endorsed a more classic linguistic point of view.

The actual results are some combination of the two, and very hard to understand. (I don’t want to try characterizing the authors’ interpretation, because I’m still not sure I completely understand it. I recommend reading the paper instead.)

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Kerstin Meints, Kim Plunkett, Paul Harris (2008). Eating apples and houseplants: Typicality constraints on thematic roles in early verb learning Language and Cognitive Processes, 23 (3), 434-463 DOI: 10.1080/01690960701726232

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