Mind & Body

This Adorable Test Measures Children's Grasp of Language Rules

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If you find one rock and then you find another, you would have two rocks. If you find one shell and then you find another, you would have two shells. If you gave your beach companion one kiss and then gave them another, you'd have given them two kisses. In all of these cases, you're turning the singular noun into the plural, but you're doing it slightly differently each time. The question is: How do people know to do it differently? Did they just learn these words on their own, or did they learn the rules they follow? To answer this question, a linguist in the 1950s quizzed small children with a measure that's come to be known as the Wug Test.

This Is a Wug

Turning "shell" into "shells" and "fish" into "fishes" are examples of morphology, or word formation. A morpheme is an irreducible unit of meaning — if a word were an atom, morphemes would be the protons and electrons. "Fish" is a single morpheme, for instance, while "fishes" is made up of the morphemes "fish" and "es," and "meaning" is made up of the morphemes "mean" and "ing." Meanwhile, an allomorph is kind of like a synonym for a morpheme: "s" makes a word plural, as in "rocks," but so do its allomorphs "s" (pronounced "z" as in "shells") and "es" (pronounced "ez" as in "fishes"). Knowing which allomorph to use in which case is an essential part of knowing the rules of language.

For a study published in 1958, the psycholinguist Jean Berko Gleason set out to understand how children think about morphology. But that was no small feat. She knew she couldn't just ask kids to recite the plural forms of existing English words because there was no way to know whether they simply memorized the words themselves instead of understanding the rules for forming them.

Instead, she came up with nonsense words. Here's how the test went down: An experimenter would show the child a card with colorful pictures on it, then read what was written on the card. For example, a card might feature a bird-like creature with the following text:

"This is a WUG.

Now there is another one.

There are two of them.

There are two ____."

The child would have never heard of a wug, but if they knew the rules of morphology, they could easily answer correctly: "There are two wugs," pronouncing the "s" like a "z."

The test didn't only deal with plural forms. It also measured the children's ability to perform all sorts of inflection, including making nouns possessive ("niz" to "niz's"), making verbs past-tense ("rick" to "ricked") or third-person singular ("naz" to "nazzes"), and making adjectives comparative ("quirky" to "quirkier") and superlative ("quirkiest"). It also tested their understanding of compound words with questions like "Why do you think a blackboard is called a blackboard?" (The correct answer would be "Because it's a board that is black.")

The participants included preschool through first-grade students, between 4 and 7 years old. For comparison, they also tested a group of adults, whose answers they used as the "correct" responses when rating the children's answers.

Mighty Morphin' Morphemes

Berko Gleason found that, unsurprisingly, children's grasp of morphological rules got better with age: First graders did significantly better than preschoolers on about half of the 26 questions. But the participants as a whole were more successful on some questions than others. Turning "wug" into "wugs" seemed to be the easiest for them — in fact, the percentage of children who got that right was the same as for turning the real word "glass" into "glasses."

It wasn't quite as simple to pronounce a word like "kra" or "lun" as the plural "kras" or "luns" because, as Berko Gleason writes, you could end these words with an "s" or a "z" sound and still have a possible English word. Same goes with the nonsense word "heaf" — you could make it "heafs" or "heaves," but because adults themselves were split on their answers, that made either form correct and led to a greater percentage of children getting it right.

The cutest result may have been in the compound words, which test whether children can pick out the individual morphemes in words like "blackboard" and "Thanksgiving." Very few children gave the kinds of answers that adults did, which took into account both parts of the compound word — i.e. "Thanksgiving is called Thanksgiving because the pilgrims gave thanks." Instead, most children either repeated the word or gave a definition of it. Many children, however, had their own imagined explanations for how these words got their names. One participant said, "Breakfast is called breakfast because you have to eat it fast when you rush to school"; another said, "A handkerchief is a thing you hold in your hand, and you go 'kerchoo.'"

Despite the children's spotty success, the results were enough for Berko Gleason to conclude that children really do possess what linguists call "productive morphological capabilities." In other words, they know the basic rules of language and aren't just reciting memorized words.

When it came to children's grasp of language rules, Berko Gleason wrote, "The picture that emerged was one of consistency, regularity, and simplicity." This study demonstrated not only that children could transform words in this way, but that they had a grasp of these rules much earlier in life than previously assumed. Whether it's shells or wugs, kids can handle as many as you can give 'em.

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Learn more about how little ones grasp language in "How Babies Talk: The Magic and Mystery of Language in the First Three Years of Life" by Roberta Michnick Golinkoff and Kathy Hirsh-Pasek. The audiobook is free with an Audible trial. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer October 6, 2019

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