Exploring Word Learning in a High-Density Longitudinal Corpus

Exploring Word Learning in a High-Density Longitudinal Corpus Brandon C. Roy (bcroy@media.mit.edu) Michael C. Frank (mcfrank@mit.edu) The Media Laboratory Massachusetts Institute of Technology Department of Brain and Cognitive Sciences Massachusetts Institute of Technology Deb Roy (dkroy@media.mit.edu) The Media Laboratory Massachusetts Institute of Technology Abstract What is the role of the linguistic environment in children’s early word learning? Here we provide a preliminary analy- sis of one child’s linguistic development, using a portion of the high-density longitudinal data collected for the Human Speechome Project. We focus particularly on the develop- ment of the child’s productive vocabulary from the age of 9 to 24 months and the relationship between the child’s language development and the caregivers’ speech. We find significant correlations between input frequencies and age of acquisition for individual words. In addition, caregivers’ utterance length, type-token ratio, and proportion of single-word utterances all show significant temporal relationships with the child’s devel- opment, suggesting that caregivers “tune” their utterances to the linguistic ability of the child. Keywords: Language acquisition; word learning; corpus data Language Development and the Environment What is the role of the linguistic environment in a child’s ac- quisition of language? In attempts to understand the nature of the mechanisms underlying language acquisition, input- uptake correlations have the potential to provide deep insight. If particular aspects of children’s input are predictive of their later language development, such findings could powerfully illuminate the nature of children’s language learning strate- gies and mechanisms and the relationship of linguistic knowl- edge and experience. Systematic studies of child-directed speech (CDS) dating back to the late 1960’s have established that CDS has special characteristics including shorter utterance lengths, exagger- ated prosody, high redundancy, and referential content tied to immediate context (Snow & Ferguson, 1977). Initial in- vestigations of the facilitative role of CDS focused primarily on development of syntax. Early findings were contradictory, however, and the overall picture remains mixed (Newport et al., 1977; Furrow et al., 1979; Pine, 1995). More recent stud- ies of the role of the environment on lexical development proved to be clearer. For example, studies have shown that the total amount of CDS predicts children’s vocabulary size and rate of growth (Huttenlocher et al., 1991; Hart & Risley, 1995) and the frequency of specific words within CDS pre- dicts the age of acquisition of those words (Huttenlocher et al., 1991; Goodman et al., 2008). Despite the quantity of work in this area, however, our overall understanding of the role of the environment in lan- guage development remains limited by the lack of appropriate observational data. Historically, most longitudinal studies of language development have relied on observations from just two or a few points in time, leading to difficulties in construct- ing a complete picture of the continuous developmental pro- cess. Driven by new technologies, the methodological land- scape is now changing. Higher density longitudinal studies are emerging that provide valuable new perspectives on long- standing questions. For example, by analyzing 90-120 minute audio recordings of children’s home environments every two weeks from 9-15 months of age, Brent & Siskind (2001) shed new light on the role of words spoken in isolation by show- ing that their presence in CDS predicted age of acquisition of those words. More recently, Lieven et al. (in press) recorded 28-30 hours of audio over a 6-week period in the homes of four toddlers yielding 100,000+ word corpora of CDS and speech by children from each home. These data were used to trace the relationship between a child’s utterances over time in support of a constructivist theory of grammar development. Motivated by the goal of obtaining a more complete and naturalistic longitudinal record of child development—and establishing new tools and methods for replicating such ef- forts in the future—the Human Speechome Project (HSP) was launched with the aim of recording the first two to three years of one child’s development at home in rich detail (Roy et al., 2006). This paper provides an overview of the HSP project and corpus, and the human-machine collaborative process for audio analysis. We then present an initial anal- ysis on a subset of the audio portion of this corpus focusing on CDS and lexical development. The Human Speechome Project The goal of HSP is to study early language development through analysis of audio and video recordings of the first two to three years of one child’s life. The home of the fam- ily of one of the authors (DR) with a newborn was outfitted with fourteen microphones and eleven omnidirectional cam- eras. Audio was recorded from ceiling mounted boundary layer microphones at 16 bit resolution with a sampling rate of 48 KHz. Due to the unique acoustic properties of boundary layer microphones, most speech throughout the house includ- ing very quiet speech was captured with sufficient clarity to enable reliable transcription. Video was also recorded to cap- ture non-linguistic context using high resolution fisheye lens video cameras that provide a bird’s-eye view of people, ob- jects, and activity throughout the home. Recordings were made from birth to the child’s third birth- day with the highest density of recordings focused on the first