GoKawiilTo examine the neural responses, we analysed the average ERPs time-locked to the acoustic tone onsets of the bassline notes of the auditory stimuli (Figure 2). Adults’ ERPs, which served as a benchmark to interpret infants’ responses, included an early positivity peaking at 37 ms post-stimulus (so-called ‘P50,’ here reaching an average amplitude of 1.05 µV), followed by a later negativity peaking at 87 ms post-stimulus (so-called ‘N100,’ here reaching an amplitude of -0.43 µV) and a second positivity peaking at 158 ms post-stimulus (so-called ‘P200,’ here reaching an amplitude of 0.85 µV). This triphasic EEG pattern has been widely observed in adults in response to fast-rising auditory stimuli and across different contexts (Novembre et al., 2018; Pratt et al., 2008; Remijn et al., 2014; Somervail et al., 2021). Cluster-based permutation analyses, contrasting the ERPs elicited by music vs shuffled music, revealed that the amplitude of the P50 – hereafter referred to as P1 – was larger in response to music compared to shuffled music, particularly within the time range comprised between -17 and 58 ms post-stimulus (cluster-t=366.16, p=0.016). Similarly, the amplitude of the following P200 - hereafter referred to as P2 – was larger in response to music than to shuffled music, particularly within the time range of 114-190 ms post-stimulus (cluster-t=395.42, p=0.016). Both P1 and P2 responses were observed over frontocentral electrodes, showing a medial distribution, in line with previous literature (e.g. Lijffijt et al., 2009).
Figure 2 with 1 supplement with 1 supplement see all Download asset Open asset Developmental changes in neural responses to musical structure and pitch. Event-related potentials (ERPs) elicited by the notes within the music (orange, left) vs shuffled music (khaki, left) as well as by the notes comprised within the high-pitch (blue, right) vs low-pitch music (purple, right), across four groups of participants (plotted in ascending order of age, from top to bottom): 3-, 6-, 12-month-old infants (N=79) and adults (N=26). Grand-average ERPs are averaged across electrodes within the significant cluster of each age group in the music condition (except for pitch condition comparison in the 6-month-olds, which used the cluster from that contrast). Shaded areas indicate the standard error. ERPs show progressively shorter latencies with increasing age. All groups exhibited a P1 response, while only older infants (12-month-olds) and adults additionally exhibited a P2. Music elicited a larger P1 (and, when present, P2) amplitude compared to shuffled music, notably across all groups (time ranges associated with a significant difference are indicated by horizontal black lines). The topography of this neural response (averaged across the time window of the P1 cluster) in the music condition appears to shift more medially with increasing age. Colorbars beneath topography plots index EEG amplitude values.
All infants’ ERPs showed a P1 response, while a P2 response was observed only in 12-month-old infants, albeit with a lower amplitude than the P1. The P1 latency decreased (χ²(2)=391.25, p<0.001), and its amplitude increased (χ²(2)=8.59, p=0.014) with age (Figure 2, left column). Importantly, and in line with the adults’ data, all infant groups exhibited enhanced P1 amplitudes in response to music compared to shuffled music. Actually, across all groups, shuffled music did not elicit as clear ERPs as the ones elicited by music. Cluster-based permutation (n Perm = 1000) testing revealed that 3-month-old infants’ P1 amplitude was enhanced between 177 and 305 ms post-stimulus (cluster-t=1111.90, p=0.002). Within this window, the P1 peaked at 212 ms and reached an average amplitude of 1.8 µV. The topography included a frontocentral cluster with a slight right lateralization. In 6-month-old infants, the amplitude of the P1 was enhanced between 116 and 284 ms post-stimulus (cluster-t=1401.60, p=0.002), peaking at 165 ms and reaching an amplitude of 2.8 µV. The topography included a few (centro-) parietal electrodes in addition to several frontocentral electrodes, with a bilateral activation. In 12-month-old infants, the amplitude of the neural response to music was enhanced in a two-peak cluster (cluster-t=1416.30, p=0.002). The first peak, an infantile P1, occurred between 104 and 227 ms, peaked at 146 ms post-stimulus, and reached an amplitude of 3.1 µV. Notably, 12-month-old infants exhibited an additional positivity, namely an infantile P2, possibly homologous to the P200 observed in adults. The P2 ranged from 307 to 325 ms post-stimulus and peaked at 316 ms, with an average amplitude of 1.0 µV. The topographies remained frontocentral but were more medial, similar to adults.
To rule out the possibility that increased neural responses in the music condition reflected differences in inter-tone temporal spacing (see IOI range in Table 1), we performed control analyses, including only epochs from the shuffled music condition for which the prior or subsequent IOI exceeded the median IOI duration. The resulting ERPs in the shuffled music condition were highly similar to those reported above (compare Figure 2 with Figure 2—figure supplement 1), and the difference between the music and shuffled music conditions remained significant across all age groups (p<0.05). These findings indicate that the observed effects are not solely attributable to variations in inter-tone spacing but also reflect sensitivity to musical structure.