Semantic Development Acquisition of words and their meanings First words at about 12 months Initially this is a slow, gradual process Maybe learn a couple of words a week Object words, commands, some social words (bye-bye) Then, several months after it begins, word learning speeds up dramatically Usually begins when child’s vocabulary is around 50-100 words The “Vocabulary Burst” or “Naming Explosion

The Vocabulary Burst Rapid increase in the rate of word learning in very early childhood. Estimated that the average 5-year-old knows about 6000 words If child knows 100 words at 18-months, this means they learn 5900 words over the next 3 ½ years. Almost 5 words/day “Fast-Mapping” How do they do it? Naming insight: Everything has a name and there’s a name for everything Application of word-learning strategies or principles specific to this task:

Word Learning Principles Why do we need them? Quine’s (1960) “gavagai” example Taxonomic assumption Words are labels for categories of things Whole-object assumption Words label whole objects, not parts or attributes Mutual Exclusivity Avoid attaching two labels to the same object The disambiguation effect (Merriman & Bowman, 1989)

Word-learning errors Undergeneralization Overgeneralization Using a word to narrowly, e.g. only using “cat” for your own pet More common in early word learning, prior to naming explosion Overgeneralization Using a word too broadly, e.g. using “cat” to label cats, dogs, cows, etc… More common after the naming explosion Do they really think a cow is a cat? More likely it is “lexical gap filling”

Syntactic development Shortly after the vocabulary burst, kids begin to combine words. “mommy sock” Early word combinations typically express a common set of meanings Recurrence “More bottle” Negation “No bottle” Possession “My bottle” Actor-action “Baby eat”

The 14 Morphemes (Brown, 1970) 14 early-learned morphemes that are essential to learning English syntax plural –s, posessive –s, progressive –ing, past –ed, irregular past, third person -s in, on the, a copula be, auxiliary be (contracted and uncontracted) Vastly increase the complexity of language Use Mean Length of Utterance in Morphemes as a measure of children’s syntactic development.

What are children learning? Are they simply remembering and imitating what they hear or are they learning syntactic rules? Good evidence that they are learning rules How do children treat words they’ve never heard before: The “Wug” Test Overregularization of syntactic patterns

The “Wug” Test (Berko, 1958) This is a wug. Now there are two of them. There are two --------. Can do this for possessive, progressive, past morphemes

How do kids do? Children as young as 3 productively use all of these morphemes on novel words -ing is acquired the earliest (consistency of form) Plural, possessive, and past allomorphs next /wugz/ /wuks/ /wucIz/ /wugd/ /wukd/ /wudId/ Those adding the extra vowel are acquired a little later, but even children as young as 4 regularly apply the correct allomorph to the stem.

Overregularization Application of morphological and syntactic rules Typically see this with irregular forms Goed, eated, hurted Mouses, mooses, childs Children as old as 7 overregularize as will adults learning a new language Syntactic rules are represented as such, the exceptions are stored explicitly. Double markings: “wented” or “mices”