What are the two strategies for amplitude encoding in the auditory system?

• A. Frequency Coding
• B. Amplitude ↔ Displacement and Population Coding
• C. Temporal Coding
• D. Phase Coding

Answer: (B)

The way sound intensity is represented relies on two complementary strategies: hair cell displacement and population coding. When a sound vibrates the basilar membrane, the resulting deflection of the hair bundles (stereocilia) determines the magnitude of the mechanotransduction current in each hair cell. Larger deflections produce bigger receptor potentials, more neurotransmitter release, and higher firing rates from the connected auditory nerve fibers. That direct link between the amount of hair bundle displacement (the mechanical input) and the amount of neural signal is a primary way amplitude is encoded.

At the same time, the auditory system uses population coding to cover a wide dynamic range of intensities. Not all fibers have identical thresholds or dynamic ranges, so as sound becomes louder, more fibers are recruited and/or their firing rates increase across the population. This distributed activity across many neurons provides a robust, scalable representation of amplitude that complements the single-cell transduction signal from hair bundle displacement.

Other concepts like frequency, temporal, or phase coding relate more to how the timing and pitch of sound are represented rather than the amplitude across a broad range.