Four-month-old Infants Process Own Mother's Voice Faster Than Unfamiliar Voices--electrical Signs of Sensitization in Infant Brain

Four-month-old infants heard their own mother's voice and a voice of an unfamiliar female as "oddballs" in a stream of acoustic information. The neuronal processing from 50 to 500 ms (as evaluated with event-related brain potentials, ERPs) was expected to be obligatory and from 500 to 900 ms to include cognitive processing. There was a clear shift in the processing speed between the mother's and unfamiliar voices at around 350 ms. While earlier obligatory ERP components occurred at significantly shorter latency to the mother's voice, later endogenous components were significantly delayed relative to the unfamiliar voice. The amplitude differences between the experimental stimuli were clearest for the last ERP potential, which presumably includes largest cognitive component. The size of the potential was significantly lower for mother than for unfamiliar voice. The results suggest that the behaviorally well-documented mutual sensitization between infant and mother and the special importance of output from mother is seen as an enhanced arousal to mother's voice and as signs of a clear memory template for own mother's voice at very early age.