Final answer:
Phase locking refers to the consistent phase angle firing of auditory neurons and occurs up to frequencies around 1000-1500 Hz in humans, with variability depending on individual and biological factors.
Step-by-step explanation:
The concept of phase locking refers to the ability of neurons, especially auditory neurons, to fire at a consistent phase angle of a sound wave's cycle. This phenomenon occurs up to a frequency that varies depending on the context in which it is being discussed. However, in the context of human auditory perception, phase locking typically occurs for frequencies below approximately 1000-1500 Hz, with declining effectiveness as the frequency increases. For example, auditory nerve fibers can phase-lock to frequencies up to about 1000 Hz in many mammals. As frequencies rise beyond this range, phase locking becomes less precise until it is no longer observable at higher frequencies. The exact frequency at which phase locking stops being effective can be subject to individual variability and specific biological limitations.