Newborn infants are able to learn every existing language of the world. During their first years of life the flexibility to learn every language restricts to their native language. Similarly, infants‘ neuronal processing mechanisms for speech vary during language development to finally become adult-like.
This raises the question where exactly two-year-old infants are situated regarding this continuum. In this regard, phonotactics is investigated as a crucial linguistic information during early language acquisition. Phonotactics describes the legal combinations of phonemes in a given language. The present study asks whether two-year-old infants are still open to new linguistic regularities like newborns or whether they are already more sensitive to regularities necessary in their native language?
To answer this question 20 two-years-olds were tested by functional near-infrared-spectroscopy (fNIRS). They were acoustically exposed to phonotactically legal and illegal stimuli.
Results reveal that unlike adults, two-year-olds do not show an adult-like lateralization to the left-hemisphere but still use both hemispheres. Phonotactically legal stimuli lead to larger neuronal activations compared to illegal stimuli, especially in children with a high vocabulary size. This suggests a successful discrimination ability between native and non-native regularities. Nevertheless all infants showed a great openness to learn also foreign phonotactic rules. Thus, it can be concluded that two-year-olds are not strictly focused on their native language.