The "eardrum artifact" in ipsilateral reflex measurements

A source of error in ipsilateral reflex measurements with impedance methods is explained. It is shown that the inherent non-linearity of the cavity represented by the ear canal and tympanic membrane gives rise to an artifact in the measurement of acoustic impedance which is synchronous with the stimulus. The magnitude of the artifact increases with the intensity of the stimulus, but is relatively insensitive to the frequency of the stimulus. A practical method for measuring the magnitude of the artifact is described.