Fig. 8. Zebra finch B4 showed a decrease in duration of two syllables and yet retained air sac pressure and airflow throughout. In A, the change in duration of the long expiratory pulse (612 ms) is evident by the comparison between pre-injection pressure (blue) and pressure after two injections (green). B shows the decreased pressure in each syllable in areas where the pressure pulses remain similar in spite of the duration change. The descent of the difference in the second syllable is due to change in duration. C shows the cumulative flow of each syllable, which shows the overall decrease in airflow from pre-injection (blue) to one injection (red) and two injections (green). Sound is shown as rectified and integrated amplitude (D) and spectrographically (E). The change from smooth frequency modulation (pre-injection) to a complex harmonic structure (two injections) can be seen in the long syllable in the spectrograms.