All-day recordings to investigate vocabulary development: A case study of a trilingual toddler.

Major innovations are becoming available for research in language development and disorders. Among these innovations, recent tools allow naturalistic recording in children's homes and automated analysis to facilitate representative sampling. The present study employed all-day recordings during the second year of life in a child exposed to three languages, using a fully-wearable battery-powered recorder, with automated analysis to locate appropriate time periods for coding. This method made representative sampling possible, and afforded the opportunity for a case study indicating that language spoken directly to the child had dramatically more effect on vocabulary learning than audible language not spoken to the child, as indicated by chi-square analyses of the child's verbal output and input in each of the languages. The work provides perspective on the role of learning words by overhearing in childhood, and suggests the value of representative naturalistic sampling as a means of research on vocabulary acquisition.