Abstract
The speech infants hear, in the first year of life before they themselves begin to speak, is mainly multi-word utterances, without clear pauses between the
words. Thus to construct the initial vocabulary they need to begin speaking themselves, infants need to learn how to segment words from speech. Indeed,
there is evidence that segmentation ability in the first year of life correlates positively with vocabulary size at two years. This evidence has come principally from studies of segmentation using the behavioralheadturn-preference procedure. If infants first hear words in isolation, and then recognise these familiarised words when they occur later in sentences, they have shown that they can segment individual words out of multi-word utterances. An electrophysiological analogue to this behavioralprocedure, measuring Event-Related Potentials (ERPs) was however later developed by Kooijman. This allowed, for the first time, an online assessment of infants’ word segmentation. Kooijmantested seven-and ten-month-olds; the ten-month-olds showed a clear recognition response (in the form of a left negativity) for familiarised words heard later in sentences, relative to unfamiliar words. This showed that the ten-month-olds indeed had the ability to segment speech. Such segmentation behaviorwas not, however, consistently present in the seven-month-olds. We here report three studies relating this ERP measure of speech segmentation to later language development. First, we divided the seven-month-old infants tested by Kooijmaninto two sub-groups: those with an ERP effect similar to the 10-month-olds’ pattern, and those without such an effect. When re-tested at three years of age, the former group displayed significantly higher language scores than the latter group. Second, we examined whether ten-month-olds can recognize words that have previously been presented just once, within an utterance. Recognition was again indicated by a left-frontal negativity, and presence and size of this response proved in later testing to be related to vocabulary size, both at 12 and at 24 months. Third, we conducted a study in which both familiarization and test phases consisted of continuous sentences. Again we observed the same recognition response in the infant brain, and the patterning of this response was once more related to later performance, this time in a test of recognition of known words at 16 months. Hence, with a variety of measures, we see that a consistently observed ERP effect of word segmentation serves as a direct predictor of the degree of later language development.
