Purr

The mechanism by which cats purr is an object of speculation, with different hypotheses proposed. An early idea was that purring is a hemodynamic process where sound is produced as the blood runs through the thorax. There is a unique "neural oscillator" in the cat's brain of uncertain significance. Although the mechanism has not yet been fully explained, recent studies have inferred it could be the result of oscillatory mechanisms in the central nervous system. Studies have also shown that purring can be caused through electrically stimulating the infundibular region of the cat's brain, suggesting central control. Vocal folds/laryngeal muscles One hypothesis, backed by electromyographic studies, is that cats produce the purring noise by using the vocal folds or the muscles of the larynx to alternately dilate and constrict the glottis rapidly, causing air vibrations during inhalation and exhalation. Combined with the steady inhalation and exhalation of air as the cat breathes, a purring noise is produced with strong harmonics. Degree of hyoid ossification No cat can both purr and roar. The subdivision of the Felidae into "purring cats" (Felinae) on one hand and "roaring cats" (Pantherinae) on the other goes back to Owen and was definitively introduced by Pocock, based on whether the hyoid bone of the larynx is incompletely ("roarers") or completely ("purrers") ossified; however, Weissengruber et al. argued that the ability of a cat species to purr is not affected by the anatomy of its hyoid. The "roaring cats" (lion, Panthera leo; tiger, P. tigris; jaguar, P. onca; leopard, P. pardus) have an incompletely ossified hyoid, which, according to this hypothesis, enables them to roar but not to purr; however, the snow leopard (Uncia uncia, or P. uncia), as the fifth felid species with an incompletely ossified hyoid, purrs. All remaining species of the family Felidae ("purring cats") have a completely ossified hyoid, which enables them to purr but not to roar. Based on a technical acoustic definition of roaring, the presence of this vocalization type depends on specific characteristics of the vocal folds and an elongated vocal tract, which is rendered possible by an incompletely ossified hyoid. ==Frequency, amplitude, and respiratory variation==

Domestic cats purr at a frequency of 20 to 30 vibrations per second. Schötz & Eklund studied purring in four domestic cats and found that the fundamental frequency varied between 20.94 and 27.21 Hz for egressive phases and between 23.0 and 26.09 Hz for ingressive phases. Schötz & Eklund also observed considerable variation between the four cats as regards relative amplitude, duration and frequency between egressive and ingressive phases, but that this variation occurred within the same general range. In a follow-up study of purring in four adult cheetahs, Eklund, Peters, Weise & Munro found that egressive phases were longer than ingressive phases in all four cheetahs. Likewise, ingressive phases had a lower frequency than egressive phases in all four cheetahs. Mean frequency were between 19.3 Hz and 20.5 Hz in ingressive phases, and between 21.9 Hz and 23.4 Hz in egressive phases. Moreover, the amplitude was louder in the egressive phases in four cheetahs. Eklund & Peters compared purring in adult, subadult and juvenile cheetahs and reported that while there was considerable variation across most of the parameters analyzed (amplitude, phase duration, cycles per phase and fundamental frequency) – mainly attributable to degree of relaxation/agitation in the animals resting or playing– previously reported observations that ingressive phases tend to be lower in frequency were largely confirmed. There were no major differences in these parameters as a function of age. ==Purpose==

In domestic cats, many signals that occur when interacting with humans seem to originate from when the animal was dependent on the mother. Cats have been observed to purr for most of their lifespan, starting from when they were young and suckling from their mother. Purring may be a signaling mechanism of reassurance between mother cats and nursing kittens. Post-nursing cats often purr as a sign of contentment when being petted, becoming relaxed or eating. Some purring may be a signal to another animal that the purring cat does not pose a threat. Cats have been shown to have different types of purrs depending on situations. For example, purring appears to be a way for cats to signal their caretakers for food. This purring has a high-frequency component not present in other purrs. These are called solicitation purrs (when the cat is seeking a result) and non-solicitation purrs, and the two are distinguishable to humans. In a study, 50 people listened to recordings of purrs recorded in solicitation and non-solicitation situations at the same amplitude. Humans regularly judged the solicitation purrs as less pleasant and more urgent than the non-solicitation purrs. ==See also==