Naunton's Masking Dilemma Revisited.

Background: Pure-tone audiometry is essential in diagnosing clinical hearing loss. Masking of the nontest ear is mandatory for determining accurate hearing thresholds in the presence of asymmetrical levels between the two ears and for ascertaining the presence of a conductive hearing loss. Paradoxically, over masking occurs when the intensity of the required masking noise to the contralateral ear is such that it exceeds interaural cranial attenuation by an amount sufficient to mask the test ear. Ralph F Naunton was the first to describe this phenomenon, which has since been known as "Naunton's masking dilemma."

Methods: A formula was derived mathematically to predict when Naunton's masking dilemma might occur in air and bone conduction. Review of Ralph F Naunton's primary works and related publications was performed.

Results: Our derived mathematical formulae predict when "Naunton's masking dilemma" may occur. During air conduction testing, a masking dilemma may occur when the sum of the air/bone gaps is greater than or equal to twice the interaural attenuation minus 15 dB (Σ ABGNTE+TE ≥ 2 × IA - 15 dB). During bone conduction testing, a masking dilemma may occur when the air-bone gap of the nontest ear is greater than or equal to the interaural attenuation minus 15 dB (ABGNTE ≥ IAAIR - 15 dB).

Conclusion: Naunton's masking dilemma imposes a significant limitation to conventional audiometric testing. To the best of our knowledge, we think this is the first time that Naunton's masking dilemma has been represented in a simplified mathematical equation.