Hierarchical prediction in toddlers: Semantic and phonological development

• Toddlers predict words in constrained sentences from 18 months of age. • Semantic competitor prediction emerges by 24 months. • Phonological competitor prediction emerges by 30 months. • Prediction follows a semantic-to-phonological developmental trajectory. • Results support hierarchical models of language prediction in toddlers. The predictive processing framework suggests that the brain generates semantic and phonological predictions to facilitate real-time language comprehension. While adults engage in both types of prediction, how these abilities develop in early childhood remains unclear. The present study explores the emergence of semantic and phonological predictions in toddlers aged 18, 24, and 30 months in three preferential looking experiments. Toddlers were presented with highly constrained sentence contexts paired with visual stimuli to assess their predictive abilities. Experiment 1 measured word prediction accuracy using predictable and unpredictable sentence conditions. Experiment 2 tested semantic prediction by introducing a semantic competitor, while Experiment 3 evaluated phonological prediction using phonologically similar competitors. Results showed that by 18 months, toddlers exhibited anticipatory looks toward the expected target. By 24 months, toddlers showed anticipatory looks toward not only the predictable target word but also toward semantically related items, and by 30 months, this pattern extended to phonologically related items. This developmental pattern—characterized by the earlier emergence of semantic relations followed by phonological relations—is consistent with the idea that semantic predictions provide a foundation for the subsequent development of phonological predictions. We discuss the data considering different prediction mechanisms, such as hierarchical predictive coding, prediction-by-production, and prediction through associations; we propose that these mechanisms are complementary components of a unified predictive system.