FIGURE 1.

Distortion product otoacoustic emissions (DPOAEs) are sounds emitted by normal cochlear hair cells. This figure describes the biological origin of DPOAEs and the methods used to measure them. A microphone probe with two speakers is inserted and sealed in the external ear canal. The two speakers present two tones of different frequencies (f1 and f2) independently. These two tones are transmitted across the external and middle ear, reaching the cochlear receptor. In the inner ear (cochlear receptor), the two tones generate mechanical distortions at different cochlea basilar membrane positions, including the 2f1‐f2 position, the most widely used DPOAE in clinical and research settings. The presence of DPOAEs depends on the normal functioning of outer hair cells (OHCs). The OHCs possess electromotility, a physiological mechanism in which these cells transduce membrane voltage changes into mechanical vibrations, a physiological process known as the “cochlear amplifier.” As a result of this biological amplification, f1 and f2 tones interact and generate mechanical distortions at different cochlear positions, including the 2f1‐f2 position. These distortions travel back to the external ear, where they can be recorded with a sensitive microphone and measured as a DPOAE at a specific frequency and amplitude in dB sound pressure level (SPL).