Extended Data Fig. 6 |. Phrases’ durations and onset times also correlate to their sequence, but cannot fully account for HVC activity.

a. (Δf/f₀)_denoised signal traces (ROI 18, bird 3) during one phrase type (red) arranged by its duration. Colored barcode annotates the final phrase in the sequence. b. The signal correlates to the red phrase’s duration (r (95%CI), p: 2-sided Pearson’s test for N=32 songs. Colors match barcode in panel a). c. Sonograms of two phrase sequences. d-g. ROI signals during N=36 sequences containing the last 2 phrases in panel c have various relations to the duration of the middle (purple) phrase (Scatter plots as in panel b. Dashed lines indicate significant correlations) and the identity of the 1^st phrase (colors, 1-way ANOVA (F,p,η²(95% CI)) tests the effect on the signal Σ. Whiskers, boxes, and lines show full range, 1^st and 3^rd quartiles, and medians). d. Signal correlation with phrase duration is completely entangled with the signal’s sequence preference and does not apply in separate preceding contexts (red, p > 0.5). e. Signal correlation with phrase duration is influenced by the signal’s sequence preference but also exists in the preferred sequence context separately (red). f. Signal duration correlation is observed within each single preceding context separately, but the correlation reduces across all songs. g. Similar to panel a, but the signal is in the 2^nd phrase, not the 3^rd. h. Distributions of 1-way ANOVA p-values (y-axis, whiskers, boxes, and red lines show full range, 1^st and third quartiles, and medians) relating phrase identity and signal for adjacent phrases (N=279 independent 1^st order tests, left) and non-adjacent phrases (N=119 independent ≥2^nd order tests, right). Tests are also done on residuals of signals, after discounting the following variables: variance explained by the target phrase duration, the timing of all phrase edges in the test sequence, and the time-in-song (x-axis, effects accumulated left to right by multivariate linear regression, see methods). Colored, dashed lines mark 0.05 and 0.1 p-values. i. Effect size (η² denotes frac. variance accounted for by the signals’ context dependence) of past (red) and future (blue) 1-way ANOVA tests for 1st order (left, N=279 tests) and ≥2nd order (right, N=119) correlations. Difference of the mean value (μ) is tested using 1-sided bootstrap shuffles (p-values, methods).