Double-evoked otoacoustic emissions. I. Measurement theory and nonlinear coherence

An evoked otoacoustic emission (OAE) measurement technique is proposed to better control for probe distortion. Each double-evoking (2E) stimulus sequence includes three, equal-duration subsequences defined as follows: s₁(t) is a single chirp or click, s₂(t)= εs₁(t-τ) is a copy of s₁ with relative amplitude ε and delay τ, and s₁₂(t)=s₁(t)+s₂(t) is the superposition of the first two stimuli. The pressure response to each subsequence is p₁, p₂, and p₁₂, respectively. The double chirp-evoked distortion product (2ChDP) and double click-evoked otoacoustic emission (2CEOAE) are defined by p(D) =p₁₂-(p₁ + p₂). The 2ChDP response may be time compressed to analyze as an equivalent 2CEOAE response. The 2E response family provides a complementary representation between DP measurements and double click-evoked OAE measurements. A technique based on nonlinear coherence quantifies random noise in terms of a nonlinear signal-to-noise ratio.