Consistency and variability in pitch and tempo in infants' everyday musical lives.

Most North American infants hear music every day. Familiar songs are especially effective in capturing infants' attention, influencing their social behavior, and regulating their emotional responses. To the extent that songs are familiar because they are repeated over time, quantifying song features across renditions will yield insights into their powerful roles in organizing early human behavior. Comprehensive theories of musical development and auditory learning must consider the contexts in which infants' emerging abilities are observed, and the nature of the stimuli available to them in their everyday lives. The current study quantifies the pitches and tempos of live song renditions in one day of experiences at home. We conducted secondary analyses of recordings of 27 infants' auditory environments (MendozaMusic corpus, Mendoza & Fausey, 2018), collected by infant-worn recorders (LENA). For each singer in the infant's environment (44), we identified renditions of their most frequent song and analyzed starting tonic pitches and average tempos. There were large individual differences across singers, with some displaying consistency (e.g., repeating a classic lullaby 11 h apart, at similar tempos, one semitone apart), and others, dramatic variations (e.g., singing a pop song 30 bpm and six semitones apart). In contrast with prior laboratory evidence suggesting remarkable stability in song renditions, this everyday heterogeneity suggests new hypotheses about when, how, and why infants recognize and respond to certain songs.