Early vocabulary improvement has more to do with the "quality" of the interactions in which the words are used rather than the sheer quantity of speech directed at young children, find psychologists at the University of Pennsylvania.
Moreover, the study shows that, unlike quantity, the quality of these interactions is not related to the parents' socioeconomic status.
The study was conducted by professors John Trueswell and Lila Gleitman, both of the Department of Psychology in Penn's School of Arts and Sciences, as well as by Erica Cartmill and Susan Goldin-Meadow of the University of Chicago. Also contributing to the study were Benjamin Armstrong III of Penn and Tamara Medina of Drexel University.
Knowing how critical early-language acquisition is to a person's future success, Trueswell and Gleitman have long investigated the mechanisms involved in how children learn their first words.
One of their previous studies suggests that children learn these words in what might be described as a "eureka" moment - that is, only after "highly informative" examples of speech that clearly connect the word to the thing it refers to.
The researchers suspected these highly informative examples would matter much more than the sheer amount of talk in the home when it came to which children learned more words.
To determine if this was the case, they set out to track the long-term effects of these examples, seeing if children who had been exposed to them more often did better on a vocabulary test three years later. However, to begin this study, the researchers first had to determine what constituted highly informative speech.
To quantify this phenomenon, the researchers visited more than 50 families from various backgrounds in their homes and videotaped parents interacting with their children.
They made these visits when the children were 14 months old and then again four months later.
They found a surprising amount of variability: the parents who provided the highest rate of highly informative examples did so 38 percent of the time, while those who provided the lowest rate did so only 4 percent of the time.
The effect of this discrepancy was clear when the researchers tracked how well each of the children did on a standard vocabulary test three years later.
The more frequently a child heard highly informative examples of speech, the better he or she did on these tests.
The study is published in the Proceedings of the National Academy of Sciences.