Which type of otoacoustic emission is elicited when the ear is stimulated by two different pure tones, requiring two oscillators and two attenuators?

• A. Spontaneous OAEs
• B. Transient evoked OAEs
• C. Distortion-product OAEs
• D. Fine-structure OAEs

Answer: (C)

Two-tone stimulation taps the cochlea’s nonlinear response to create distortions, so the emission produced is a distortion-product otoacoustic emission. When two pure tones are presented, the outer hair cells generate new frequencies, most famously at 2f1 − f2, which is the distortion product measured in the ear. To produce and detect these products you need two independent sound sources (two oscillators) and two gain controls (two attenuators) to set the two primaries and observe the resulting emission. Spontaneous OAEs occur without any stimulus, and transient evoked OAEs come from broadband clicks or brief stimuli; fine-structure refers to the intricate spectral pattern seen within distortion-product OAEs rather than the eliciting method itself.