Melodic notes trigger earlier and larger auditory cortex responses than tonic notes

Evidence

The six adapted responses from the bars with the same sequence type (tonic or melodic) were shown to be very similar in that paper, and this made it possible to do a powerful, four-dipole fit with two dipoles focusing on the N1m temporal window and two focusing on the P2m temporal window. The fit isolated melodic and tonic generators in HG in both hemispheres, near the position of the melodic generator in the current experiment. Figure 2 presents a comparison of the average, adapted responses in the data of Patterson et al. ( 2015 ) to the tonic notes from bars 1 and 3 (red lines) and the melodic notes of bars 2 and 4 (blue lines). The left and right panels show the TRs from the source waves obtained with the N1m and P2m temporal windows respectively. The figure shows that the technique reveals a double dissociation; the N1m is prominent in the N1m temporal window (left panel) but the P2m is not; whereas the P2m is prominent in the P2m temporal window (right panel), but N1m is not. Moreover, the adapted melodic notes (blue) produce a larger P2m (right panel) and a larger N1m (left panel) than the adapted tonic notes (red). … Both panels of Fig. 2 also show that the N1m peak occurs earlier in the melodic TR (blue), whereas one might have thought that it would take longer to produce a melodic response than a tonic response (latency diffpassive = 25.63 ms, crit-t = 14.15, p < 0.05; latency diffactive = 14.22 ms, crit-t = 8.21, p < 0.05). Although the peak delay differences might seem small, the timing of the N1m peak is one of the most precise statistics in MEG data, and these differences are highly significant—more so than the N1m amplitude differences in these panels (amplitude diffpassive = 2.74 nAm, crit-t = 2.6, n.s.; amplitude diffactive = 5.52 nAm, crit-t = 5.35, p < 0.05). — Dijk, Pim van, Physiology, Psychoacoustics and…, 4719

Both panels of Fig. 2 also show that the N1m peak occurs earlier in the melodic TR (blue), whereas one might have thought that it would take longer to produce a melodic response than a tonic response (latency diffpassive = 25.63 ms, crit-t = 14.15, p < 0.05; latency diffactive = 14.22 ms, crit-t = 8.21, p < 0.05). Although the peak delay differences might seem small, the timing of the N1m peak is one of the most precise statistics in MEG data, and these differences are highly significant—more so than the N1m amplitude differences in these panels (amplitude diffpassive = 2.74 nAm, crit-t = 2.6, n.s.; amplitude diffactive = 5.52 nAm, crit-t = 5.35, p < 0.05). — Dijk, Pim van, Physiology, Psychoacoustics and…, 4727

Categorization

• XREF: Connects to prior knowledge of ERPs/N1m as the standard auditory evoked component, and to the adaptation/oddball literature showing stimulus novelty modulates N1m latency.
• QUESTION: Why would a melodic (presumably more complex) note produce an earlier peak than a simple tonic? The authors flag this as counterintuitive—worth understanding the mechanism.
• corroborated: 2 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 4719; Dijk, Pim van, Physiology, Psychoacoustics and…, 4727