Shared understanding and idiosyncratic expression in early vocabularies.

Area of Science:

• Child Development
• Linguistics
• Developmental Psychology

Background:

• Understanding vocabulary acquisition in toddlers is crucial for developmental milestones.
• Individual differences in early language development are significant but not fully understood.
• The structure of comprehension versus production lexicons in early development requires further investigation.

Purpose of the Study:

• To quantify the extent of shared vocabulary among toddlers across different countries.
• To investigate developmental changes in vocabulary overlap for both comprehension and production.
• To explore the structural differences between toddlers' receptive and expressive language.

Main Methods:

• Analysis of large-scale data from the Child Development Inventory (CDI) covering 14,607 infants and toddlers.
• Measurement of lexical variability in both word comprehension and production.
• Comparison of vocabulary overlap at different developmental stages and lexicon sizes.

Main Results:

• Early toddler lexicons show substantial overlap.
• Beyond approximately 100 words, toddlers exhibit greater shared vocabulary in comprehension than in production.
• Expressive vocabulary variability decreases after two years of age, indicating a shift towards a common core lexicon.

Conclusions:

• Toddlers' comprehension abilities are generalized, while their production abilities foster unique expressive voices.
• Developmental trajectories of receptive and expressive vocabularies differ significantly in early childhood.
• Lexical variability in toddlers follows an inverted U-shaped curve, influenced by various developmental factors.