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Audition, or hearing, is the process by which the auditory system converts pressure waves from the environment into meaningful sounds. This capability is fundamental for human experience, enabling communication through spoken language, the appreciation of music, and the perception of environmental sounds.

Audition (Hearing)

Refers to the purity of a sound and is influenced by the timing, amplitude, and frequency of the sound waves combined. For example, the timbre of a sound is what makes different musical instruments playing the same note and loudness sound distinct.

Timbre

The anatomy of the human auditory system comprises several anatomical structures that capture sound waves and transmit them inward. Sound waves initially enter the auditory canal. The visible external ear includes the pinna, which leads to the tympanic membrane (eardrum). Beyond this are the ossicles, which consist of the malleus, incus, and stapes. Further inward, a close-up of the inner ear reveals additional structures, including the semicircular canals, utricle, saccule, oval window, cochlea, basilar membrane, and hair cells.

Anatomy of the Auditory System

People can discriminate changes in frequency between two tones by about 2 Hz for sounds up to 2000 Hz. Pitch relies on the subjective expereince of sound, which means frequency of sound is not the only determinant of pitch. There are two complementary ways that pitch information is encoded.

Encoding pitch information

Auditory signals are able to integrate information from both ears in order to identify the sourse of a sound. This helps with allerting danger, potential mates, or other situational information that is necessary for survival and normal activities throughout the day. Humans have an accuracy of about 1 degree horizontally around their head, and may animals demonstrate even higher accuracy. There are two types of binaural (two-ear)cues that help with localization on the horizontal plane; intensity and latency.

Auditory systems for localizing sound

Sound transduction is the continuous process where sound waves funneled into the auditory canal cause eardrum vibrations that move the ossicles. The stapes then presses the cochlea's oval window, moving fluid that enlarges hair cells on the basilar membrane, which ultimately send neural impulses to the brain via the auditory nerve.

Sound Transduction in the Ear

Based on the fundamental principle that hearing involves converting pressure waves from the environment into sound, explain why the person's hearing was temporarily affected and what happened when they yawned.

Explaining an Everyday Auditory Phenomenon

Sound localization is the auditory ability to identify the origin of a sound within an environment, which is a crucial aspect of hearing. This ability is analogous to depth perception in the visual system. Just as depth perception relies on monocular and binocular visual cues, the auditory system utilizes both monaural (one-eared) and binaural (two-eared) cues to pinpoint where a sound is coming from.

Sound Localization

A musician plays a note on a guitar. They then tighten a string and pluck it more gently, producing a second note that is perceived as higher in pitch and quieter. What physical changes in the sound waves correspond to this perceptual change?

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