One thing many of us tend to take for granted is the ability to learn the first language. How do children develop their language? A well known experiment in the field of Linguistics is the Wug Test.

The Wug test was conducted by Jean Berko Gleason in 1958. It explored how children learned their first language in terms of English morphemes. Morpheme is the smallest meaningful unit of a language that construct words. For example, in English, the singular and plural forms of DOG and DOGS both have only 1 word. The difference is the singular noun DOG is constructed from 1 morpheme while the plural noun DOGS is made up of 2 morphemes: DOG and the plural morpheme -S

The wug test tried to find out whether children learn English morphemes by memorizing singular and plural forms such as DOG and DOGS independently or whether they know the morphological rule which states that: the noun DOG plus the plural morpheme -S makes the plural form DOGS:

If children learn the morphemes by memorization, when they encounter a “nonce” noun like “Wug”, a made up bird, they may not be able to generalize the rule to them and use the plural “Wugs” form as the words WUG and WUGS are independent and they need to encounter the plural form WUGS to know the word. If children learned the morpheme by rule extraction, when they encountered a “nonce” word, they may still be able to generate the rule to them and use the plural form “Wugs”

To test for these hypotheses, two groups of participants were recruited:
The Preschooler group included 12 girls and 7 boys from 4-5 years old.
The First graders group included 26 boys and 35 girls from 5.5 to 7 years old

The children were presented with the cards with pictures of nonce words that follow the sound combinations of English. The experimenter pointed to the picture and read the text. Then, the child filled in the missing word and the child’s response was phonemically noted. For example:
“This is a wug. Now there is another one. There are two of them. There are two __”
The morphemes that the researchers focused on were 28 structures of morphemes in plurals, past tense, progressive, third person singular, comparative and superlative of adjectives and singular, and plural possessive.

The most important results suggested that first, there was no difference in gender: girls and boys performed equally in their accuracy. Second, both Preschoolers and First graders could use correctly plural allomorphs: voiceless /-s/ after a voiceless consonant and voiced /-z/ after a voiced consonant but they could not generalize the correct use of the plural allomorph /-əz/ after s and /z/ even though they had the real word vocabulary of plural form such as the plural form glasses. The same pattern was found for past tense: the children could use correctly /-d/ and /-t/ allomorphs but could not generalize the correct use of /-əd/.

Preschoolers and first graders successfully generate the allomorphs of plural morphemes -s and -z to their phonological conditions in nonce words. That is, the plural form of WUG was WUGS, they exhibited the knowledge of morpheme rules. This finding supported the rule extraction hypothesis that children learn English morphemes by rule extraction, not by memorizing plural and singular forms independently. The difficulty in generating the correct use of allomorph /-əz/ was possibly due to the constrictive context this allomorph appears

So, the most important take home message is, acquiring first language in children is not merely a matter of memorization, drills, or repetition, but more the development of a mental representation of implicit knowledge of the language