Sparse labels, no problems: Infant categorization under challenging conditions.

Labeling promotes infants' object categorization even when labels are rare. By 2 years, infants engage in "semi-supervised learning" (SSL), integrating labeled and unlabeled exemplars to learn categories. However, everyday learning contexts pose substantial challenges for infants' SSL. Here, two studies (n = 74, 51% female, 62% non-Hispanic White, 18% multiracial, 8% Asian, 6% Black, M_age  = 27.3 months, collected 2018-2020) implemented a familiarization-novelty preference paradigm assessing 2-year-olds' SSL when (i) exemplars from the target category are interspersed with other objects (Study 1, d = .67) and (ii) multiple categories are learned simultaneously (Study 2, d = .74). The findings indicate 2-year-olds' SSL is robust enough to support object categorization despite substantial challenges posed by everyday learning contexts.