Toddlers' understanding and use of verbal negation in inferential reasoning search tasks.

Past research has demonstrated that young children and nonhuman animals are able to reason by elimination ("If not A, then B") by relying on visual cues such as seeing that one container is empty. Other research has shown that young children can solve similar, simple inferential reasoning tasks where "emptiness" is conveyed verbally through negation (e.g., "The toy is not in the box"). However, it is unclear whether these tasks involved reasoning through the disjunctive syllogism, which requires the representation of logical negation (NOT A) and disjunction (A OR B) or simpler, nondeductive strategies. In Study 1, we extended this work by investigating whether 2-year-olds can infer the location of a toy in typical two-location elimination trials, when given both affirmative and negative sentences, and more complex three-location trials, when information about emptiness was conveyed verbally and visually. Younger 2-year-olds performed significantly better on the search task when hearing affirmative than negative sentences, whereas older 2-year-olds were equally successful with both types of sentences. Study 2 examined children's ability to use verbal negation to solve a more complex deductive task involving disjunctive syllogism. Results showed that, in this linguistic version of the disjunctive reasoning task, both 2.5- and 3-year-olds made accurate inferences about the location of a reward, unlike prior (nonlinguistic) evidence that demonstrated this ability in 3-year-olds but not in younger children. We conclude that by the end of their second year of life, children have a robust understanding of negation which they can apply in abstract reasoning.