From 'ah' to 'bah': social feedback loops for speech sounds at key points of developmental transition.

Social feedback is a driving force for speech development. A recent study provided a key finding to explain how contingent responses influence developmental change: infant speech-related vocalizations are contingent on responses to prior speech-related vocalizations (Warlaumont et al., 2014). However, the study did not distinguish between different speech-related vocalizations, vowel-like (V) and consonant-vowel (CV) vocalizations, which is important because CV vocalizations are a precursor to words. The present study explored parents' responses to infants' vocalizations and infants' subsequent vocal production at a point when vocalizations become more like adult speech. The relative proportion of CVs following contingent responses to CV did not differ between 10- and 12-months-olds; however, there was only a significant contingent relationship between responses to CV and subsequent CV production in 12-month-olds. Results suggest a developmental transition and a social feedback loop for the production of more developmentally advanced sounds when infants are learning their first words.