How does the auditory system encode frequency?

How does the auditory system encode frequency?

• A. The basilar membrane vibrates at the same frequency as the incoming sound, leading to phase-locked auditory nerve spikes.
• B. The amplitude of nerve spikes encodes frequency.
• C. Frequency is encoded by the outer ear resonance.
• D. Frequency is encoded by the tympanic membrane vibrating at a constant amplitude.

Answer: (C)

Frequency information is encoded primarily by the cochlea’s organized response along its length and, for low frequencies, by the timing of neural spikes. The basilar membrane is stiffer at the base and more flexible at the apex, so high-frequency sounds produce maximal displacement near the base while low-frequency sounds peak toward the apex. Hair cells at the location of maximal displacement transduce that mechanical motion into neural signals, creating a spatial map of frequency along the cochlea (tonotopy). In addition, for lower frequencies, auditory nerve fibers tend to fire in synchrony with the waveform, providing a temporal code that preserves the timing of the sound. Outer ear resonance and the tympanic membrane’s merely transmitting vibration with some amplitude variation influence what spectral components reach the cochlea, but they do not themselves encode frequency in the way the cochlea does.

Frequency information is encoded primarily by the cochlea’s organized response along its length and, for low frequencies, by the timing of neural spikes. The basilar membrane is stiffer at the base and more flexible at the apex, so high-frequency sounds produce maximal displacement near the base while low-frequency sounds peak toward the apex. Hair cells at the location of maximal displacement transduce that mechanical motion into neural signals, creating a spatial map of frequency along the cochlea (tonotopy). In addition, for lower frequencies, auditory nerve fibers tend to fire in synchrony with the waveform, providing a temporal code that preserves the timing of the sound. Outer ear resonance and the tympanic membrane’s merely transmitting vibration with some amplitude variation influence what spectral components reach the cochlea, but they do not themselves encode frequency in the way the cochlea does.