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How does the brain identify pitch from signals sent by the auditory nerve?
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Learn about the propagation of sound waves from a point source by observing the motion of a suspended vibrating spring.
The brain identifies pitch by processing signals from the auditory nerve through two primary mechanisms related to the basilar membrane within the cochlea:
- Place Theory: The basilar membrane varies in stiffness and width along its length. High-frequency sounds cause the basal end to vibrate, while low-frequency sounds stimulate the apical end. The brain recognizes the pitch by identifying which specific group of nerve fibers is activated, corresponding to the region of the membrane vibrating most vigorously.1
- Rate (Temporal) Coding: For lower frequencies (up to approximately 3,000 Hz), the brain also utilizes the timing of nerve impulses. The auditory nerve fibers fire at intervals corresponding to the phase of the sound wave. This "phase-locking" allows the brain to interpret the frequency based on the rate of stimulation.12
For higher frequencies, the place of maximum vibration on the basilar membrane is the decisive factor for pitch recognition.1