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Introduction
Study Purposes
The data collected during the LENA Natural Language Study has resulted in a corpus of spontaneous speech data representative of the language environment of infants and toddlers (2 months - 48 months of age). Daily speech recordings collected during this study provided the basis for the development of the advanced audio processing algorithms central to the LENA System. Following Hart and Risley's (1995) seminal language development research, these data were also intended to establish normative information about patterns of talk and Adult Word Counts (AWC), Child Vocalizations (CV), and Conversational Turns (CT) in the households of infants and toddlers and to validate the earlier Hart and Risley research.
Study Overview
The LENA Natural Language Study is an ongoing multiphase data collection effort. The current paper describes Phase I, the normative data collection phase that took place between January - June 2006, and the first 18 months of Phase II, an extended longitudinal data collection phase started in July 2006. At the onset of Phase I, parents of infants and toddlers (predominantly 2 months - 36 months of age, with an additional 15 children; 37 months to 48 months) were recruited through advertisements in local newspapers and direct mail solicitation. Potential participants were selected based on demographic considerations such as the child's age and the mother's education level. Participating families in Phase I provided day-long audio recordings once per month for six months and visited LENA's child language research center for a standard evaluation by a certified speech-language pathologist. We compiled speech recording data into the LENA Natural Language Corpus from which we produced normative estimates of daily AWCs, CTs, and CVs in the language environment of infants and toddlers. Phase I audio data have been supplemented by additional audio recordings during Phase II to provide normative information for children up to 48 months old. The LENA Natural Language Study has been reviewed and approved by Essex Institutional Review Board (IRB) to help ensure that the rights and welfare of research participants were protected and that the study was conducted in an ethical manner.
Methods
Demographics
A total of 334 children ages 2 months - 48 months from monolingual English-speaking households began the normative Phase I of the LENA Natural Language Study. Due to attrition and other factors, 311 participants completed this phase. There were 329 participants who contributed at least one valid 12-hour recording during Phase I.
Inclusive/Exclusive Criteria
To ensure a representative sample, we recruited children across an even age distribution and tried to match the US census with respect to the mothers' attained education level, which has been shown to be correlated with child language development (e.g., Arterberry, Midgett, Putnick, & Bornstein, 2007). We selected families according to the following criteria:
- Age distribution: We recruited roughly eight children from each age month, ages 2 - 36 months, plus 15 children ages 37 - 48 months.
- Mother's education: The normative development sample was intended to represent the US population with respect to mothers' education level (i.e., 23% college diploma, 29% some college, 26% high school diploma and no college, 22% no high school diploma). The goal was to match this distribution for each age month interval. For example, for the eight children who were six months old at the beginning of the study, on average two of them should have had mothers with college degrees, two should have had mothers with some college experience, two should have had mothers with high school diplomas (but no college classes), and two should have had mothers who did not graduate from high school.
- Household language: Participants were selected from English-speaking households only.
- Normative language development: Families with children who had been diagnosed with a language or developmental delay or disability were excluded from the original development study, as the data were collected for the purpose of establishing normative information about a typically developing population.
We actively sought participants from a representative distribution of children who were born premature, children who attended daycare, and children who had older or younger siblings, since any of these factors could influence language development.