Her observations about vocabulary acquisition, made in an article published in the March issue of Developmental Psychology, run counter to a popularly accepted idea that some children learn words more quickly than others because of inherent differences in ability. Additionally, the study shows that girls tend to learn words more quickly than boys.
"The basis of individual differences in vocabulary growth are not well understood. It is generally assumed that the major source of individual differences in vocabulary is variation among children in the capacity to learn from incoming speech. That is, preparedness for learning language, at least with respect to vocabulary, is believed to vary across individuals," writes Huttenlocher, the William S. Gray Professor in Psychology.
"The possibility that variation in the amount of exposure is a substantial factor in vocabulary development has received little attention. Yet the acquisition of vocabulary poses an enormous learning task; the child must acquire from incoming speech a large number of pairings of sound patters with meanings," she says. "Hence, exposure is clearly critical to the acquisition of vocabulary."
studied 22 children divided into two groups. One group was seen every second month of the study for five hours. The second group was seen for three hours. Children were 16 months old at the start and 26 months old when the study concluded. The groups were recorded.
All of the parents participating in the two studies were full-time caregivers. Although the results of the study are technically only valid for parents and children, Huttenlocher says she would expect the impact of time spent speaking with children would be the same if the caregiver were another adult.
She found that there was a great range in the amount of conversation directed at children. The most talkative mothers used ten times as many words as did the least talkative mothers. The data showed substantial differences in vocabulary for children based on the amount of talking their mothers did to them.
Children of the most talkative mothers had 33 more words in their vocabulary at 16 months than did the children of mothers who were the least talkative. The difference was 131 words at 20 months and 295 words at 24 months.
The differences probably reflected the number of opportunities children had to hear a word and then try it on their own. Words that were more frequently used by a mother were the words that were learned earliest, Huttenlocher found.
The data on gender differences are both revealing and puzzling. The data show that girls' larger vocabularies do not come from mothers talking more with girls than they do with boys.
"Hence, gender differences in early vocabulary growth seem to reflect early capacity differences, not differential responses of mothers to their sons and daughters," she points out. "The breakdown of the vocabulary growth data into two shorter time-periods suggests that gender effects in acquisition of new words are already declining in the age period of 20-24 months, as suggests the existing literature which fails to find gender differences after two years."
Huttenlocher says that girls may begin maturing sooner than boys and as a result learn some of the skills necessary to reproduce language at an earlier age.
"Given the substantial relation between amount of parent speech and child vocabulary growth, it is clearly important to identify the factors affecting how much parents speak to their children," Huttenlocher writes. "Evidence from the existing literature on differences among different caretaker groups points to such factors."
More research should be done on the impact of parental speech on children's vocabulary at other points in their growth, Huttenlocher feels.
"Given the strength of the observed relation of language exposure to vocabulary growth, it is clearly important to explore the extent to which changes in speech input, initiated at later time points, might affect the trajectory of vocabulary growth," she writes.
Janellen Huttenlocher is the William S. Gray Professor of Psychology and Education and in the College.