Passage Sound Waves Propagate Through Many Conducting Structures in the Ear

Passage
Sound waves propagate through many conducting structures in the ear before they are transduced into neuronal signals.  When sound waves reach the fluid-filled cochlea, they are detected by hair cells lining the basilar membrane.  The cochlear spiral can be modeled as a resonator system because each section of the basilar membrane is sensitive to a specific frequency (Figure 1) .
Figure 1  Amplitude pattern of the basilar membrane for different frequenciesPresbycusis (age-related hearing loss) results from a combination of factors that lessens an individual's mechanical and/or neurological sensitivity to sound.  Pure tone audiometry (PTA) is used to determine an individual's ability to detect different sound frequencies and can be used to evaluate presbycusis.  A "pure" tone is characterized by a single sinusoidal waveform.  An audiogram plots the relative intensity required of a given frequency to be detected by the individual (Figure 2) .
Figure 2  Audiogram of an elderly patient exhibiting presbycusis
-Hearing loss due to loud environments can be mitigated with noise-canceling earphones, which generate a waveform that reduces the intensity of ambient noise through wave interference. For the above sound wave, the waveform generated for complete noise cancellation will be:

A) phase-shifted by half a wavelength.
B) flipped across the x-axis.
C) double the frequency.
D) the exact same wave.

Correct Answer:

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