ERP indices of word learning: What do they reflect and what do they tell us about the neural representations of early words?

At a certain point in development, infants’ mental representations of word meanings shift from low-level visual-auditory associations to higher-level connections that referentially bind word forms with semantic representations. This view of a representational transition from so-called “proto-words” to “genuine words” (Nazzi & Bertoncini, 2003) is widely accepted, but how such a change happens has been largely unknown. Does a particular state of brain maturation have to be achieved before elementary semantic representations can be established? Do genuine words develop from first-established proto-words? Do proto-words and genuine words develop independently at successive developmental stages, or does the emergence of genuine words begin parallel to the further establishments of proto-words? Until recently, it has not been investigated on which factors the transition from proto-words to genuine words depends. Moreover, even though the shift from perceptual-associative to referential semantic representations was claimed to underlie changes in infants’ behavioral development, such as the emergence of the fast mapping ability or the onset of the vocabulary spurt (e.g., Nazzi & Bertoncini, 2003), it has been unknown when exactly the supposed transition in infants’ word representations occurs