Nature and origins of the lexicon in 6-mo-olds

Abstract

Recent research reported the surprising finding that even 6-mo-olds understand common nouns [Bergelson E, Swingley D (2012) Proc Natl Acad Sci USA 109:3253-3258]. However, is their early lexicon structured and acquired like older learners? We test 6-mo-olds for a hallmark of the mature lexicon: cross-word relations. We also examine whether properties of the home environment that have been linked with lexical knowledge in older children are detectable in the initial stage of comprehension. We use a new dataset, which includes in-lab comprehension and home measures from the same infants. We find evidence for cross-word structure: On seeing two images of common nouns, infants looked significantly more at named target images when the competitor images were semantically unrelated (e.g., milk and foot) than when they were related (e.g., milk and juice), just as older learners do. We further find initial evidence for home-lab links: common noun "copresence" (i.e., whether words' referents were present and attended to in home recordings) correlated with in-lab comprehension. These findings suggest that, even in neophyte word learners, cross-word relations are formed early and the home learning environment measurably helps shape the lexicon from the outset.

Keywords: cognitive development; environmental effects; language acquisition; lexicon; word learning.

Fig. 1.

Comprehension by trial type. Dots represents each infant’s baseline-corrected proportion of target looking, per trial type (unrelated, related). Mean and 95% CIs are in black. Asterisk indicates P < 0.05 for the unrelated and related trial types; the fraction indicates the proportion of infants with positive trial-type means.

Fig. 2.

Distribution of object word utterances, by infant. Color shows utterance type [daylong audio (Left) and hour-long video (Right)]. One video was lost; one word with unclear utterance type was removed. The x axes are identically ordered by each child’s overall proportion of object words in declaratives and questions.

Fig. 3.

In-lab comprehension by proportion of object copresence. Each point indicates a given infant’s average proportion of object copresence in the audio and video home recordings (x axis) by that same infant’s subject mean in the eye-tracking experiment (y axis). Line indicates robust linear fit, with 95% CI in gray.

Fig. 4.

Item pairs in eye-tracking study. Infants saw each image pair twice. There were 16 trials in each trial type (related, unrelated), 32 trials total.