With its highly developed sense of hearing, the cat can detect a wide range of sounds at very low intensities. The cat's range of perceived vibrations is approximately three times greater than that of humans. Cats can hear lower sounds and especially much higher ones: In the ultrasound range, at frequencies above 20,000 hertz, cats seem able to perceive sounds up to 60,000 Hz! Very low intensity (approximately 5 dB) suffices, with the perceived sensation increasing largely as a function of intensity. Cats are thus able to distinguish slight variations in pitch, regardless of intensity. The concepts of auditory fatigue, adaptation, and persistence are much less pronounced in feline hearing. Cats can locate the source of sound by moving their ear flaps in different directions, each moving independently of the other.
The pinnae capture sound waves and transmit them to the outer auditory canal. Sound is thus initially reinforced through resonance (as when one speaks into a tube). The eardrum vibrates and transmits these vibrations to the osselets (hammer, anvil, and stirrup), which serve as a transformer, since the resistance to sound propagation is not the same in air (outer ear) and water (inner ear). The solid osselets transmit sound waves between the two media without information being lost through reflection.
The information is coded electrically in the cochlea, a sort of spiral passageway lined with vibratory cells connected to nerve cells. These cells are bathed in the fluid, or endolymph, contained in the cochlea. They form the organ of Corti, which is connected to the vestibulocochlear nerve.
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