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
-In Figure 2, how does the hearing threshold intensity at 1,500 Hz compare to the threshold intensity at 2,000 Hz?

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
-In Figure 2, how does the hearing threshold intensity at 1,500 Hz compare to the threshold intensity at 2,000 Hz?

Quizplus · Accepted Answer

11ecba2d_12ec_dba6_a3bf_a1d0092186a9_MD0008_00 Intensity is defined as the amount of power (energy per unit time) delivered per unit area. The intensity of sound is related to its perceived loudness and is approximately logarithmic; a ten-fold increase in sound intensity is perceived to be twice as loud. The ratio of the intensities of two sounds is measured on a base-10 logarithmic scale with units of decibels (dB): 11ecba2d_12ec_dba7_a3bf_bf3973d13e7b_MD0008_00 For every increase in 10 dB, the ratio of the intensities increases by a factor of 10 (eg, +20 dB = 10² = 100 times more intense). Conversely, the ratio of the intensities decreases by a factor of 10 for each decrease in 10 dB. From Figure 2, the hearing threshold at 1,500 Hz is 20 dB and the hearing threshold at 2000 Hz is 50 dB. Therefore, the relative intensity between the two frequencies in dB is the difference: 11ecba2d_12ec_dba8_a3bf_cbfa8fc85e33_MD0008_00 A sound that is 30 dB lower is 10³ = 1,000 times less intense (Choice C). Alternatively, this relationship can be resolved mathematically using the definition of the logarithm. (Choices A and B) Because the intensity of sound is measured on a logarithmic scale (not a linear scale), a change in 30 dB is not a 30-fold change in intensity. (Choice D) Although the hearing threshold intensity for 1,500 Hz is plotted above the hearing threshold intensity for 2,000 Hz on the audiogram figure, it is important to note that the y-axis is inverted. The hearing threshold intensity at 1,500 Hz is thus lower than that for 2,000 Hz. Educational objective: The intensity of sound is measured on a logarithmic scale with units of decibels (dB). For each decrease in 10 dB, the sound intensity decreases by a factor of 10. Therefore, a decrease in 30 dB is equal to a 1,000-fold decrease in intensity.

Passage Sound Waves Propagate Through Many Conducting Structures in the Ear