Fig. 9.

Analysis of gap durations of songs from two birds before and after bilateral medial HVC ablation is used to set the number of neurons in synaptic chains for two model birds. A: for bird 411, the duration of the gap for the atypical F-E transition is considerably longer than those for typical transitions. There is also a long gap before the atypical S-to-E transition. B: for bird 513, the atypical B-A transition gap is longer than for typical transitions. The G-A and S-A transitions are also much longer after ablation than before. In the simulations of birds 411 (C) and 513 (D) the long durations reflect the time required for activity in PAm chains to reach the end of the chains.