Different roles of prosody and repetition in infant word recognition: ERP studies in 6-, 9- and 12-month-old German infants

Previous studies have shown that infants start to detect unknown words in sentences between 7 and 10 months of age [1, 2]. In this context, the role of phonological and statistical cues in the speech input received a lot of attention [3, 4], while speech style characteristics have been widely neglected. However, parents naturally use accentuation within context and high numbers of repetitions when teaching infants new words [5, 6]. Here, we systematically investigated the impact of these conversational cues on word recognition in a familiarization-test paradigm across an age range of 6 to 12 months. When infants were repeatedly familiarized to words with or without accentuation in sentences, event-related brain potentials to word processing revealed clear developmental differences. Younger infants' processing was driven by prosodic cues, whereas older infants relied on repetition cues. In subsequent test phases, brain responses to familiarized versus new words confirmed the age-dependent reliance on different input cues forword recognition. Six-month-olds only recognized previously accentuated familiarized words. Both 9- and 12-month-olds showed recognition independent of previous accentuation, with 9-month-olds displaying an additional response to accentuated words. In summary, forprosodically salient input, infants show word segmentation and recognition at an earlier age than previously reported, emphasizing the crucial role of prosody in early language acquisition. After an initial reliance on prosodic information, repetition of a given item in the input becomes the relevant cue, indicating specific input-sensitive periods in speech segmentation within developmental steps of only three months