Fig. 4.

Phonologically greedy error correction. a Two imitation tasks (4.1, left; and 4.2, right) offering birds a choice to match syllables in the source song either to spectrally close targets (1 semitone) in the wrong sequential context (black arrows), or to slightly farther targets (2 semitones) in the correct context. b Developmental trajectories of two experimental birds trained with the imitation tasks in a. Stack plots show consecutive motif renditions following the switch to target training (day 0), colors indicate pitch of syllables B/B⁻¹/B⁺¹/B⁺²; and grayscale indicates Wiener entropy in neighboring syllables (as in Figs. 2b and 3b). Birds shifted pitch towards the spectrally closer targets, resulting in a decreased (left) or an incomplete (right) syntax match due to the acquisition of two incorrect syllable transitions (dashed arrows). c Pitch trajectories of the same experimental birds, showing pitch shifts in the direction of the spectrally closer targets (see also Supplementary Fig. 2). Note that in task 4.1 (left), the closer and farther targets are in opposite pitch directions, while in task 4.2 (right) they are in the same direction. d Left, trajectories of pitch shift towards target across experimental birds trained with task 4.1 (n = 2; daily medians averaged over the two pitch shifted syllable types in each bird). Both birds shifted towards the close targets and away from the far targets. Right, pitch and syntax shift towards target at developmental endpoint (0, source pitch/syntax; 1, full match of either close or far target/full match of target syntax, defined as 100% performance of correct transitions; −1, syntax maximally shifted away from target, defined as 100% performance of incorrect transitions; means±s.e.m. across birds). Birds increased pitch similarity, but decreased syntax similarity to target. e Left, same as d left for birds trained with task 4.2 (n = 5). Four birds shifted pitch no further than the close targets, and one bird matched the far targets. Right, pitch and syntax shift towards target at developmental endpoint (0, source pitch/syntax; 1, full match of either close or far target/full match of target syntax, defined as 100% performance of correct transitions; means±s.e.m. across birds)