Audition is the sense of hearing. It begins when sound waves—variations in air pressure—enter the ear and end when the brain interprets those vibrations as meaningful events in the world.

The outer ear funnels the waves to the eardrum. The middle ear bones amplify the vibration and transmit it to the fluid-filled cochlea of the inner ear. Hair cells along the basilar membrane convert the mechanical movement into neural signals that travel via the auditory nerve to the brainstem, thalamus, and finally the auditory cortex. Different frequencies are mapped onto different places along the basilar membrane and onto corresponding regions of cortex, giving the system its ability to distinguish pitch.

Hearing is remarkably sensitive and precise. It detects intensity differences smaller than a whisper and localizes sound sources in space by comparing the input from the two ears. Yet it is also vulnerable. Loud noise, aging, certain drugs, and disease can destroy hair cells that do not regenerate, producing permanent hearing loss.

Audition turns the invisible movement of air into the rich auditory world of speech, music, and environmental sound.