Auditory rhyme processing in expert freestyle rap lyricists and novices: An ERP study

Music and language processing share and sometimes compete for brain resources. An extreme case of such shared processing occurs in improvised rap music, in which performers, or 'lyricists', combine rhyming, rhythmic, and semantic structures of language with musical rhythm, harmony, and phrasing to create integrally meaningful musical expressions. We used event-related potentials (ERPs) to investigate how auditory rhyme sequence processing differed between expert lyricists and non-lyricists. Participants listened to rhythmically presented pseudo-word triplets each of which terminated in a full-rhyme (e.g., STEEK, PREEK; FLEEK), half-rhyme (e.g., STEEK, PREEK; FREET), or non-rhyme (e.g., STEEK, PREEK; YAME), then judged each sequence in its aesthetic (Do you 'like' the rhyme?) or technical (Is the rhyme 'perfect'?) aspect. Phonological N450 showed rhyming effects between conditions (i.e., non vs. full; half vs. full; non vs. half) similarly across groups in parietal electrodes. However, concurrent activity in frontocentral electrodes showed left-laterality in non-lyricists, but not lyricists. Furthermore, non-lyricists' responses to the three conditions were distinct in morphology and amplitude at left-hemisphere electrodes with no condition difference at right-hemisphere electrodes, while lyricists' responses to half-rhymes they deemed unsatisfactory were similar to full-rhyme at left-hemisphere electrodes, and similar to non-rhyme at right-hemisphere electrodes. The CNV response observed while waiting for the second and third pseudo-word in the sequence was more enhanced to aesthetic rhyme judgments tasks than to technical rhyme judgment tasks in non-lyricists, suggesting their investment of greater effort for aesthetic rhyme judgments. No task effects were observed in lyricists, suggesting that aesthetic and technical rhyme judgments may engage the same processes for experts. Overall, our findings suggest that extensive practice of improvised lyricism may uniquely encourage the neuroplasticity of integrated linguistic and musical feature processing in the brain.