Globally, songs are slower, higher, and use more stable pitches than speech [Stage 2 Registered Report]

What, if any, similarities and differences between song and speech are consistent across cultures? Both song and speech are found in all known human societies and are argued to share evolutionary roots and cognitive resources, yet few studies have compared similarities and differences between song and speech across languages on a global scale. We compared sets of matched song/speech recordings produced by our coauthors whose 1st/heritage languages span over 20 language families. Each recording set consists of singing, recited lyrics, and spoken description, plus an optional instrumental version of the sung melody to allow us to capture a “musi-linguistic continuum” from instrumental music to naturalistic speech. Our literature review and pilot analysis led us to make six predictions for confirmatory analysis comparing song vs. spoken descriptions: three consistent differences and three consistent similarities. For differences, we predicted that: 1) songs will have higher pitch than speech, 2) songs will be slower than speech, and 3) songs will have more stable pitch than speech. For similarities, we predicted that 4) pitch interval size, 5) timbral brightness, and 6) pitch declination will be similar for song and speech. We are initially reporting preliminary confirmatory analyses for the first 60 collaborators who provided sung/spoken recordings (the minimum sample size required to achieve 95% power with the alpha level of 0.05 for the hypothesis testing of the selected six features). These analyses suggest strong support for our first five predictions, but not our prediction regarding pitch declination, which appears inconclusive. Because our opportunistic language sample (approximately half are Indo-European languages) and unusual design involving coauthors as participants (approximately 1/5 of coauthors had some awareness of our hypotheses when we recorded our singing/speaking) could affect our results, we performed robustness analyses, which suggested that our conclusions are robust to these potential biases. Exploratory analyses suggest that the three differing features (pitch height, temporal rate, and pitch stability) also vary along our proposed musi-linguistic continuum in a cross-culturally consistent manner when comparing instrumental melodies and recited lyrics, and that male and female vocalizations consistently differ across languages, by almost one octave on average for both speech and song. Our study provides diverse cross-linguistic empirical evidence regarding the existence of cross-cultural regularities in song and speech, sheds light on factors shaping humanity’s two universal vocal communication forms, and provides rich cross-cultural data to generate new hypotheses and inform future analyses of other factors (e.g., functional context, age, musical/linguistic experience) that may shape global musical and linguistic diversity.