Functional morphemes and mechanisms of early language processing

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The distinction between lexical and functional categories is the most fundamental one in natural languages. Lexical categories include nouns, verbs, adjectives and adverbs. Functional categories include determiners, auxiliaries, tense endings, etc. Lexical categories are also called content words, as they carry the main weight of meaning in utterances. In contrast, the primary role of functional elements is to indicate grammatical relations across words. Children start talking around age one. They produce one-word speech for months and then word combinations by 18-20 months of age. Speech below age two contains content words, typically missing functional elements. This characteristic may suggest that young children do not know functional categories. However, new research from several labs including mine using perceptual measures shows that babies start processing functional items early, long before they can produce them. In my early studies I found that 0-6-month-old babies distinguish function words versus content words. I later showed that infants before age one perceive and represent specific functional items in their native language, and use them to segment adjacent words. Shortly after age one, infants understand the grammatical relations across different functional elements and use functors to categorize content words. These findings reveal that infants have more sophisticated grammatical knowledge than previously assumed. In the next cycle of my NSERC grant, I will address 2 issues in early morpho-syntactic acquisition: 1) the mechanisms underlying infants’ acquisition of function words and their grammatical relation with content words; 2) the initial learning of bound functional elements (e.g., endings such as –ing in English and –er in French) and their morphological relations with the stem (e.g., walk_walk-ing_walk-ed). For 1), we will test the hypothesis that the combined properties of weak word forms and high frequency for function words (relative to content words) enable infants to perceive them as functional elements and to use them to discover grammatical properties of content words (e.g., using determiners to categorize the adjacent word as a noun, “a/the dog”, “a/the cat”). To precisely study these properties, we will create artificial languages containing novel words, with careful manipulation of word forms and frequencies. Perceptual experiments using these materials will be conducted with one-year-olds. For 2), novel words with a familiar French ending –er and with an artificial ending will be used to test how preverbal and early verbal infants learn such endings and the morphological variation of related words. Across experiments, varying training conditions with novel word stems and endings will be used to examine input factors. We will test the hypothesis that the output of distribution-based morphological learning guides infants’ subsequent learning of word meaning. That is, infants first learn that certain forms are morphologically related (e.g., walk-walking), which then enables them to expect all forms of this variation to have the same core meaning. This hypothesis differs from the standard view that children first learn the meaning of individual words before interpreting (at a much later age) their internal morphological structure. Both 1) and 2) will test more than the learning of specific items and their relations. They will test infant’ ability to generalize structures at the abstract level. The studies will yield a better understanding of the mechanisms underlying early language development, in particular, the initial acquisition of abstract morpho-syntactic structures. They will contribute important data to the larger debate on the nature and origin of syntactic knowledge in infants.