Measurements of infants' quotidian experiences provide critical information about early development. However, the role of sampling methods in providing these measurements is rarely examined. Here we directly compare language input from hour-long video-recordings and daylong audio-recordings within the same group of 44 infants at 6 and 7 months. We compared 12 measures of language quantity and lexical diversity, talker variability, utterance-type, and object presence, finding moderate correlations across recording-types. However, video-recordings generally featured far denser noun input across these measures compared to the daylong audio-recordings, more akin to 'peak' audio hours (though not as high in talkers and word-types). Although audio-recordings captured ~10 times more awake-time than videos, the noun input in them was only 2-4 times greater. Notably, whether we compared videos to daylong audio-recordings or peak audio times, videos featured relatively fewer declaratives and more questions; furthermore, the most common video-recorded nouns were less consistent across families than the top audio-recording nouns were. Thus, hour-long videos and daylong audio-recordings revealed fairly divergent pictures of the language infants hear and learn from in their daily lives. We suggest that short video-recordings provide a dense and somewhat different sample of infants' language experiences, rather than a typical one, and should be used cautiously for extrapolation about common words, talkers, utterance-types, and contexts at larger timescales. If theories of language development are to be held accountable to 'facts on the ground' from observational data, greater care is needed to unpack the ramifications of sampling methods of early language input.
share first authorship. Elika Bergelson, Andrei Amatuni, and Shannon Dailey were in Brain and Cognitive Sciences at the University of Rochester during data collection. Authors have no conflicts of interest to declare.
For the past 25 years, researchers have investigated language input to children from high‐ and low‐socioeconomic status (SES) families. Hart and Risley first reported a “30 Million Word Gap” between high‐SES and low‐SES children. More recent studies have challenged the size or even existence of this gap. The present study is a quantitative meta‐analysis on socioeconomic differences in language input to young children, which aims to systematically integrate decades of research on this topic. We analyzed 19 studies and found a significant effect of SES on language input quantity. However, this effect was moderated by the type of language included in language quantity measures: studies that include only child‐directed speech in their language measures find a large SES difference, while studies that include all speech in a child's environment find no effect of SES. These results support recent work suggesting that methodological decisions can affect researchers' estimates of the “word gap.” Overall, we find that young children from low‐SES homes heard less child‐directed speech than children from mid‐ to high‐SES homes, though this difference was much smaller than Hart & Risley's “30 Million Word Gap.” Finally, we underscore the need for more cross‐cultural work on language development and the forces that may contribute to it, highlighting the opportunity for better integration of observational, experimental, and intervention‐based approaches.
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