In a contralateral masking threshold function, a plateau occurs at 75 dB HL, indicating the true test-ear threshold. Which value represents that true threshold?

In a contralateral masking threshold function, a plateau occurs at 75 dB HL, indicating the true test-ear threshold. Which value represents that true threshold?

• A. 50 dB HL
• B. 55 dB HL
• C. 65 dB HL
• D. 75 dB HL

Answer: (D)

In contralateral masking, you raise masking noise in the non-test ear while measuring the test ear’s threshold. As masking increases, the measured threshold in the test ear may shift due to crossover, but at a certain point the threshold stops changing—that flat portion, or plateau, shows that cross-hearing has been eliminated and the response is controlled by the true sensitivity of the test ear. That plateau value is the actual test-ear threshold. So if the plateau occurs at 75 dB HL, the true threshold for the test ear is 75 dB HL. The lower values (50, 55, 65 dB HL) would not represent the true test-ear threshold once the plateau has been reached, since crossing masking beyond that point no longer affects the test-ear result.

In contralateral masking, you raise masking noise in the non-test ear while measuring the test ear’s threshold. As masking increases, the measured threshold in the test ear may shift due to crossover, but at a certain point the threshold stops changing—that flat portion, or plateau, shows that cross-hearing has been eliminated and the response is controlled by the true sensitivity of the test ear. That plateau value is the actual test-ear threshold. So if the plateau occurs at 75 dB HL, the true threshold for the test ear is 75 dB HL. The lower values (50, 55, 65 dB HL) would not represent the true test-ear threshold once the plateau has been reached, since crossing masking beyond that point no longer affects the test-ear result.