Fig. 2.

Interruptions occurred at various points during a syllable. The intact acoustic structure of the song motif is illustrated spectrographically (A) along with the mean tracheal airflow (top trace in B) and air sac pressure (top trace in C) patterns (black lines with gray area indicate the mean ± 1 s.e.m. of 10 motifs). The two illustrated interruptions of the fourth syllable occurred late (green) and early (red) during the ongoing expiratory pressure pulse. For each interruption the difference in airflow and air sac pressure from the mean value of the complete motif are plotted (bottom traces in B and C; horizontal line indicates zero difference). The largest difference in airflow occurred after early termination of the expiratory pulse when the short deep inspiration (minibreath) of the intact motif was replaced by nearly atmospheric air sac pressure and, consequently, low airflow. Blue shading (B,C) highlights the minibreaths. Note that the last minibreath is only present before the vagotomy (black) and no longer occurs after interruption of the preceding syllable (red and green). a.u., arbitrary units.