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
-Audiometry can also be used to evaluate a subject's ability to localize a moving sound source. When the sound source is moving toward the subject, which of the following increases?

Question

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
-Audiometry can also be used to evaluate a subject's ability to localize a moving sound source. When the sound source is moving toward the subject, which of the following increases?

Quizplus · Accepted Answer

11ecba2d_12ee_624d_a3bf_1d540d8a80f7_MD0008_00 When relative motion exists between a sound source and an observer, the observed wave differs from the original frequency and wavelength. This phenomenon is known as the Doppler effect. When the sound source moves toward the observer (subject), the source generates each wave front at a location successively closer to the observer, shortening the observed wavelength. Because the propagation velocity is unchanged, the observer detects each wave at an increased frequency (rate) compared to the source frequency. The inverse relationship between frequency and wavelength can also be explained from the wave velocity equation (v = λf). (Choice A) The propagation velocity of sound waves depend only on the properties of the medium and is unaffected by the velocity of the source. (Choice B) The period T of a wave measures how long one cycle (or one wavelength) takes to pass through a fixed point. Because period is the inverse of frequency (T = 1/f), the observed period will decrease if the sound source is moving toward the observer. (Choice D) The observed wavelength would increase if the source and the observer are moving away from each other. Educational objective: When relative motion exists between a sound source and an observer, the observed frequency and wavelength differ from that of the original frequency and wavelength. This phenomenon is known as the Doppler effect. When the source moves toward the observer, the observed wavelength decreases and the observed frequency increases.

Passage Sound Waves Propagate Through Many Conducting Structures in the Ear