The contingency symmetry bias as a foundation of word learning: Evidence from 8-mont-olds in a matching-to-sample task

The contingency symmetry inference, the inference to generalize a learned contingency to a reverse direction, is known to be extremely difficult for non-human animal species (Lionello-DeNolf, 2009). In contrast, humans are known to have the “affirming the consequent fallacy”, which reverses the antecedent and the consequence (if P then Q: Q therefore P). The contingency symmetry bias has been long discussed in relation to the ontogenesis of language learning, as word learning requires understanding of bidirectional relationship between symbols and objects. But how this bias emerges has not been known. This research tested whether 8-month-old human infants have this bias on a matching-to-sample task. The results demonstrated the possession of this bias in human infants before they start active word learning. This bias is likely a uniquely human cognitive bias, which may explain why only humans have language.