Most mammals produce vocal sounds according to the myoelastic-aerodynamic (MEAD) principle, through self-sustaining oscillation of laryngeal tissues.1,2 In contrast, cats have long been believed to produce their low-frequency purr vocalizations through a radically different mechanism involving active muscle contractions (AMC), where neurally driven electromyographic burst patterns (typically at 20-30 Hz) cause the intrinsic laryngeal muscles to actively modulate the respiratory airflow. Direct empirical evidence for this AMC mechanism is sparse.3 Here, the fundamental frequency (fo) ranges of eight domestic cats (Felis silvestris catus) were investigated in an excised larynx setup, to test the prediction of the AMC hypothesis that vibration should be impossible without neuromuscular activity, and thus unattainable in excised larynx setups, which are based on MEAD principles. Surprisingly, all eight excised larynges produced self-sustained oscillations at typical cat purring rates. Histological analysis of cat larynges revealed the presence of connective tissue masses, up to 4 mm in diameter, embedded in the vocal fold.4 This vocal fold specialization appears to allow the unusually low fo values observed in purring. While our data do not fully reject the AMC hypothesis for purring, they show that cat larynges can easily produce sounds in the purr regime with fundamental frequencies of 25 to 30 Hz without neural input or muscular contraction. This strongly suggests that the physical and physiological basis of cat purring involves the same MEAD-based mechanisms as other cat vocalizations (e.g., meows) and most other vertebrate vocalizations but is potentially augmented by AMC.

Bioacoustics Laboratory Department of Behavioral and Cognitive Biology University of Vienna Djerassiplatz 1 Vienna 1030 Austria

Bioacoustics Laboratory Department of Behavioral and Cognitive Biology University of Vienna Djerassiplatz 1 Vienna 1030 Austria; Janette Ogg Voice Research Center Shenandoah Conservatory 1460 University Drive Winchester VA 22601 USA

Department of Livestock Sciences Research Institute of Organic Agriculture FiBL Ackerstrasse 113 Box 219 5070 Frick Switzerland

Institute of Morphology University of Veterinary Medicine Veterinärplatz 1 Vienna 1210 Austria

Voice Research Lab Department of Experimental Physics Faculty of Science Palacký University 17 listopadu 1192 12 779 00 Olomouc Czechia

References provided by Crossref.org

Application of nonlinear dynamics theory to understanding normal and pathologic voices in humans