the tendency for a neural action potential to occur at a certain phase of a pure-tone stimulus. Typically, an action potential will not occur on every cycle, but when it is generated, it tends to occur at the same point or phase in the stimulus. More generally, phase locking refers to the ability of a neuron to synchronize or follow the temporal structure of a sound. In the auditory nerve, fibers can phase lock to frequencies below 4 to 5 kHz. Phase locking underlies the ability to localize sounds based on interaural phase differences or interaural time differences (see binaural cue). Its role in monaural hearing is uncertain, but it has been proposed as a mechanism for the coding of pitch.