Interaural

Interaural is an anatomical and perceptual term relating to the two ears. In hearing science, interaural cues describe differences or relationships between the signals reaching the left and right ears, which the brain uses to locate sounds in the horizontal plane and to separate overlapping sounds.

Interaural time difference (ITD) is the difference in arrival time of a sound between the ears. ITD is most informative at low frequencies, where the waveform phase is reliable. The brain likely encodes ITD with timing-sensitive circuits in the brainstem, notably the medial superior olive, sometimes described by models of coincidence detectors. Maximum ITD is constrained by head size and is typically around 0.6 to 0.7 milliseconds in humans.

Interaural level difference (ILD) is the difference in sound pressure level between the ears, arising mainly from the head shadowing effect. ILDs are more pronounced at high frequencies, where shorter wavelengths are blocked by the head. ILDs are processed by neural pathways involving the lateral superior olive and contribute strongly to the localization of high-frequency sounds.

Interaural phase difference (IPD) refers to the phase disparity of a sound signal between ears. IPD is closely related to ITD at low frequencies but becomes less informative at higher frequencies due to phase wrapping, which limits reliable phase information.

Additional interaural measures, such as interaural coherence and interaural masking-level differences, describe how similarly the two ears’ signals vary and how binaural processing affects signal detection in noise. Collectively, interaural cues underpin much of spatial hearing, guiding sound localization and auditory scene analysis, especially in quiet versus reverberant environments.