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Mechanisms of frequency and amplitude modulation in ring dove song

Gabriël J. L. Beckers^1,*, Roderick A. Suthers² and Carel ten Cate¹

¹ Behavioural Biology, Institute of Evolutionary and Ecological Sciences, Leiden University, PO Box 9516, 2300 RA Leiden, The Netherlands
² School of Medicine, Department of Biology and Program for Neuroscience, Jordan Hall, Indiana University, Bloomington, IN 47405, USA

View larger version (40K): [in a new window]   Fig. 1. Concurrent vocalization (A), tracheal flow rate (B) and cranial thoracic air sac (CTAS) pressure (C) signals for one coo. Grey bars beneath the spectrogram and grey areas in the flow and pressure plots indicate where sound is produced, as measured from the sound oscillogram (not shown). Arrows and broken lines indicate the location of frequency jumps. The flow rate recorded during the silent intervals of the amplitude-modulated part of e2 may not reach zero because the microbead thermistor fails to track the very fast and large changes in flow rate. Note that flow rate and pressure signals have been low-pass filtered at 100 Hz to remove acoustic components and higher frequency noise.

View larger version (36K): [in a new window]   Fig. 2. Concurrent vocalization (A), interclavicular air sac pressure (ICAS) (B) and cranial thoracic air sac (CTAS) pressure (C) signals for one coo. For details, see Fig. 1.

View larger version (38K): [in a new window]   Fig. 3. Gating of sound in the amplitude-modulated part of e2, recorded in trachea (A) and interclavicular air sac pressure (ICAS) (B). Recordings A and B are from different coos but originate from the same individual. Both sound oscillograms in the trachea and ICAS show that phonation is completely interrupted by silent intervals of 10 ms. This modulation pattern corresponds to the pattern of flow rate in the trachea, which is reduced to zero or near-zero during silent intervals. ICAS pressure gradually increases in the first half of the amplitude-modulated part, although in some recordings, like in this example, the rate of increase is reduced during the sound pulses. Cranial thoracic air sac (CTAS) pressure patterns are similar to those in the ICAS in this part of the coo and are therefore not shown.

View larger version (32K): [in a new window]   Fig. 4. An example of a frequency jump in e1 [recorded in interclavicular air sac pressure (ICAS)], in which fundamental frequency (f0) jumps from approximately 525 Hz to 675 Hz within 5 ms. (A) Oscillogram (top) and spectrogram (bottom) of complete e1. (B) Detail of jump (time frame is indicated by broken lines in A) in which the oscillogram is superimposed on the spectrogram. The oscillogram shows that sound is not interrupted during frequency jumps. Although harmonic overtones are present in ICAS-recorded coo vocalizations, spectrograms here show only f0, which is the sound component that radiates from the animal. Note that the shape of the sound waveform in the ICAS is different before and after the frequency jump. Spectrogram settings: time step, 1.8 ms; frame length, 25 ms; dynamic range, 10 dB. The signal has been pass-band filtered from 300 Hz to 2500 Hz.

View larger version (14K): [in a new window]   Fig. 5. Detail of concurrent modulation of frequency and interclavicular air sac pressure (ICAS) pressure in a segment of e2. The position of the segment within the coo is indicated in the spectrogram (top right-hand corner). Frequency of phonation was determined at 8-ms intervals with an autocorrelation algorithm (Boersma, 1993) using the microphone-recorded vocalization. Signals have not been adjusted horizontally for the delay of a few ms for the sound to reach the microphone.

View larger version (29K): [in a new window]   Fig. 6. Coo frequency plotted against interclavicular air sac pressure (ICAS) pressure, cranial thoracic air sac (CTAS) pressure and tracheal air flow. Each plot represents a single, complete coo, and circles indicate value pairs as measured in 3-ms time frames of that coo. Circles are coded on a colour scale so that the development over time within a coo can be traced. Vertical arrows and horizontal arrows indicate the beginning and end of a coo, respectively. Each row contains three representative coos, originating from different individuals.

View larger version (16K): [in a new window]   Fig. 7. Association of coo fundamental frequency with tracheal flow rate, and interclavicular air sac pressure (ICAS) and cranial thoracic air sac (CTAS) pressure. Lower-case letters correspond to the doves listed in Table 1: a, RD5; b, RD1; c, RD2; d, RD2; e, RD3; f, RD4.