Longitudinal associations between production and comprehension of nouns and verbs in Kiswahili

Children’s first words are frequently recorded to be nouns, rather than verbs, but data from some languages (notably some Asian and African languages including Mandarin, Korean and Ngas) and some methodologies (especially spontaneous speech recordings) suggest that verbs can be represented as early as nouns. Variables that potentially impact early verb knowledge include the structure of the language children are learning and whether it is verb production or comprehension that is investigated. We investigated longitudinal data from Kenya of children’s (N=500) vocabulary production and comprehension using Communicative Development Inventories (CDIs). Children’s caregivers completed overlapping inventories designed for younger infants (completed at age 12 months and designed for ages 8-16 months), and for older toddlers, (parallel forms completed at age 18 and 24 months and designed for ages 16-30 months). The inventories were structured to include words acquired at equivalent ages across word classes (e.g. nouns acquired at a median age of 11 months and verbs acquired at the same median age) but the interactions between word classes and children’s age and the modality in which they know the word (comprehension only or production as well) indicate that nouns and verbs do not follow the same trajectory across acquisition. Nouns emerge relatively earlier in production and comprehension while verbs emerge earlier in comprehension and their production increases as children grow older. We conclude that the findings of Goldfield (2000) and of Stolt et al. (2008) are also true for these Bantu languages: that the noun advantage in early words is seen in studies where production is emphasised, and early verb knowledge can be missed if comprehension is not assessed.