(A) Across hemispheres, effective HVC stimulation times are complementary. Shown are sound-amplitude stack plots for left HVC stimulation (left) and for right HVC stimulation (right). Corresponding LE curves (filled) are plotted against each other in the center to illustrate the alternating stimulation effectiveness. The CC between left and right LE curves in this bird is −0.62. Inset (long black arrow): a zoom into the harmonic stack reveals no obvious relation between spectral syllable composition and right/left LE curves shown below: The transition from left to right effectiveness (right arrow) occurs in the middle of the harmonic stack where there is no apparent song change.

(B) Within hemispheres, effective stimulation times are strongly overlapping. Shown are sound-amplitude stack plots for HVC stimulation in right hemisphere (HVC-R) and for ipsilateral LMAN stimulation (LMAN-R). Corresponding LE curves (filled) are plotted against each other in the center to illustrate the alternating stimulation effectiveness. The CC between left and right LE curves in this bird is 0.65.

(C) Bar plot, showing the average CC of LE curves for stimulation in opposite hemispheres (top) and in the same hemispheres (bottom). Symbols indicate CCs in individual birds: for unilateral HVC-HVC stimulation using two electrode pairs (crosses), for unilateral HVC-LMAN stimulation (diamonds), and for bilateral HVC-HVC stimulation (circles).