Early Word Comprehension in Infants: Replication and Extension

Abstract

A handful of recent experimental reports have shown that infants of 6 to 9 months know the meanings of some common words. Here, we replicate and extend these findings. With a new set of items, we show that when young infants (age 6-16 months, n=49) are presented with side-by-side video clips depicting various common early words, and one clip is named in a sentence, they look at the named video at above-chance rates. We demonstrate anew that infants understand common words by 6-9 months, and that performance increases substantially around 14 months. The results imply that 6-9 month olds' failure to understand words not referring to objects (verbs, adjectives, performatives) in a similar prior study is not attributable to the use of dynamic video depictions. Thus, 6-9 month olds' experience of spoken language includes some understanding of common words for concrete objects, but relatively impoverished comprehension of other words.

Fig. 1

Target looking performance in each infant. Data are subject mean difference scores calculated over the 367–4000ms window. These were calculated by averaging the six item-pair mean difference scores for each subject. The shape of the symbol indicates which order manipulation condition infants were in (circles indicate “random”, triangles indicate “fixed”). The color of the lines indicates the age group used for a subset of analyses; see text for details. The black line indicates the output of a loess smoother (a locally-fitted polynomial regression), with the grey zone indicating standard errors of this fit.

Fig. 2

Time course of infants’ picture fixation over all item-pairs, averaged over infants in three age groups. The ordinate shows the mean proportion of infants who were looking at the named (target) picture at each moment in time. The abscissa shows time from the onset of the target word, determined for each individual trial. Error bars indicate SEMs, with means computed over subjects in each age range, with an overlaid smooth using GAMs (generalized additive models with integrated smoothness estimation). At all three ages, target fixation rose from about 0.50 (chance) shortly after the onset of the spoken word. Overall, target-looking increased with age across the age groups. Black vertical lines indicate the window over which target looking was calculated.

Fig. 3

Item-pair mean difference scores within each age group (three left panels), and subject means by age group (right panel). Error bars for subject means represent bootstrapped nonparametric 95% confidence intervals.

Fig. 4

Relationship between parental reports of infants’ total production vocabulary, as measured by the CDI, and subject mean difference scores, by age-bin. Children reported to say zero words are indicated by open symbols; children saying at least one word are indicated by filled symbols. The scale of the abscissa varies among the three plots.