Do early meanings of negation map onto a fully-fledged negation concept in infancy?

Young children acquire an amazing knowledge base, rapidly learning from, and even going beyond the observable evidence. They arrive at forming abstract concepts and generalizations and recruit logical operations. The question whether young infants can already rely on abstract logical operations, such as disjunction or negation, or whether these operations emerge gradually over development has recently become a central topic of interest. Here we target this question by focusing on infants' early understanding of negation. According to one view, negation comprehension is initially restricted to a narrow range of meanings (such as rejection or non-existence) and only much later infants develop a broader understanding that maps onto a fully-fledged negation concept. Alternatively, however, infants may rely on a fully-fledged negation concept from early on, but some forms of negation may pose more mapping and processing difficulties than others. Here we tested infants' understanding of two syntactically and semantically different forms of negation, existential negation and propositional denial in a language (Hungarian) that has a separate negative particle for each, and thus the two negation forms can be directly compared. We engaged 15- and 18-month-old infants in a search task where they had to find a toy in one out of two locations based on verbal utterances referring to the object at one of the locations involving existential negation (Nincsen - not.be.3SG) or propositional denial (Nem itt van - not here be.3SG). In Experiments 1-3 we found a parallel development for these two kinds of negation. 18-month-olds successfully comprehended both, while 15-month-olds were at chance for both. In Experiment 4 we excluded the possibility that 15-month-olds' chance performance is explained by task-related difficulties, as they succeeded in a similar, but nonverbal task. Thus, 15-month-olds likely still have not solved the mapping for the two negation forms. The parallel performance of the two age groups with the two negation types (failing or succeeding on both) is consistent with the hypothesis that different forms of negation rely on similar conceptual underpinnings already in early development.