Minimal gains for minimal pairs: Difficulty in learning similar-sounding words continues into preschool

A critical indicator of spoken language knowledge is the ability to discern the finest possible distinctions that exist between words in a language-minimal pairs, for example, the distinction between the novel words beesh and peesh. Infants differentiate similar-sounding novel labels like "bih" and "dih" by 17 months of age or earlier in the context of word learning. Adult word learners readily distinguish similar-sounding words. What is unclear is the shape of learning between infancy and adulthood: Is there a nonlinear increase early in development, or is there protracted improvement as experience with spoken language amasses? Three experiments tested monolingual English-speaking children aged 3 to 6 years and young adults. Children underperformed when learning minimal-pair words compared with adults (Experiment 1), compared with learning dissimilar words even when speech materials were optimized for young children (Experiment 2), and when the number of word instances during learning was quadrupled (Experiment 3). Nonetheless, the youngest group readily recognized familiar minimal pairs (Experiment 3). Results are consistent with a lengthy trajectory for detailed sound pattern learning in one's native language(s), although other interpretations are possible. Suggestions for research on developmental trajectories across various age ranges are made.