Amplitude and frequency modulation control of sound production in a mechanical model of the avian syrinx

Birdsong has developed into one of the important models for motor control of learned behaviour and shows many parallels with speech acquisition in humans. However, there are several experimental limitations to studying the vocal organ – the syrinx – in vivo. The multidisciplinary approach of combining experimental data and mathematical modelling has greatly improved the understanding of neural control and peripheral motor dynamics of sound generation in birds. Here, we present a simple mechanical model of the syrinx that facilitates detailed study of vibrations and sound production. Our model resembles the `starling resistor', a collapsible tube model, and consists of a tube with a single membrane in its casing, suspended in an external pressure chamber and driven by various pressure patterns. With this design, we can separately control `bronchial' pressure and tension in the oscillating membrane and generate a wide variety of `syllables' with simple sweeps of the control parameters. We show that the membrane exhibits high frequency, self-sustained oscillations in the audio range (>600 Hz fundamental frequency) using laser Doppler vibrometry, and systematically explore the conditions for sound production of the model in its control space. The fundamental frequency of the sound increases with tension in three membranes with different stiffness and mass. The lower-bound fundamental frequency increases with membrane mass. The membrane vibrations are strongly coupled to the resonance properties of the distal tube, most likely because of its reflective properties to sound waves. Our model is a gross simplification of the complex morphology found in birds, and more closely resembles mathematical models of the syrinx. Our results confirm several assumptions underlying existing mathematical models in a complex geometr

Songbirds use pulse tone register in two voices to generate low-frequency sound

The principal physical mechanism of sound generation is similar in songbirds and humans, despite large differences in their vocal organs. Whereas vocal fold dynamics in the human larynx are well characterized, the vibratory behaviour of the sound-generating labia in the songbird vocal organ, the syrinx, is unknown. We present the first high-speed video records of the intact syrinx during induced phonation. The syrinx of anaesthetized crows shows a vibration pattern of the labia similar to that of the human vocal fry register. Acoustic pulses result from short opening of the labia, and pulse generation alternates between the left and right sound sources. Spontaneously calling crows can also generate similar pulse characteristics with only one sound generator. Airflow recordings in zebra finches and starlings show that pulse tone sounds can be generated unilaterally, synchronously or by alternating between the two sides. Vocal fry-like dynamics therefore represent a common production mechanism for low-frequency sounds in songbirds. These results also illustrate that complex vibration patterns can emerge from the mechanical properties of the coupled sound generators in the syrinx. The use of vocal fry-like dynamics in the songbird syrinx extends the similarity to this unusual vocal register with mammalian sound production mechanisms

Social Rank Influences the Distribution of Blood Leukocyte Subsets in Female Growing Pigs

The effect of high (DOM) and low (SUB) social rank on blood immune variables was examined in female  growing pigs. Pigs were mixed with unfamiliar pigs at 9 weeks of age and kept in stable groups of 4 pigs for  5 weeks. Social rank was determined using a feeding competition test. SUB pigs showed reduced growth  as compared to DOM pigs confirming their lower social status. Blood was sampled for immunological assessments  immediately before grouping the pigs and again after the 5 weeks of social housing. White Blood  Cell (WBC) counts, percentage of CD4 positive cells (CD4+), percentage of CD8 positive cells (CD8+), percentage  of swine leukocyte antigen II (SLAII) carrying cells, LPS-stimulated Toll-like Receptor 4 (TLR4)  expression, and LPS-stimulated tumor necrosis factor-alpha (TNF-) responsiveness were determined at  both times. IgG and IgM concentrations were measured following the 5 weeks of social housing only.  From the WBC counts it was found that the percentage of neutrophils was higher in SUB pigs and the neutrophil  to lymphocyte ratio was higher in DOM pigs. The percentage of CD4+ cells decreased with time in  both DOM and SUB pigs, but only significantly in SUB pigs. The percentage of CD8+ cells was higher in  SUB pigs than in DOM pigs and decreased with time in both DOM and SUB pigs. In addition, SUB pigs  had a higher ex vivo TNF- responsiveness as compared to DOM pigs. Both the percentage of SLAII carrying  cells and LPS-stimulated TLR4 expression increased with time, but here no significant effect of social  rank was found. In addition, neither IgG nor IgM concentrations showed any relationship with social rank.  The findings indicate that social rank influences the distribution of blood leukocyte subsets in female growing  pigs, suggesting that the pig would be a good model for investigating the effects of long-term immunomodulation  on health.

Evolutionary loss of complexity in human vocal anatomy as an adaptation for speech

Human speech production obeys the same acoustic principles as vocal production in other animals but has distinctive features: A stable vocal source is filtered by rapidly changing formant frequencies. To understand speech evolution, we examined a wide range of primates, combining observations of phonation with mathematical modeling. We found that source stability relies upon simplifications in laryngeal anatomy, specifically the loss of air sacs and vocal membranes. We conclude that the evolutionary loss of vocal membranes allows human speech to mostly avoid the spontaneous nonlinear phenomena and acoustic chaos common in other primate vocalizations. This loss allows our larynx to produce stable, harmonic-rich phonation, ideally highlighting formant changes that convey most phonetic information. Paradoxically, the increased complexity of human spoken language thus followed simplification of our laryngeal anatomy.</jats:p