Detecting dead regions using psychophysical tuning curves: a comparison of simultaneous and forward masking.

A dead region (DR) is a region of the cochlea where there are no functioning inner hair cells and/or neurones. We compared the edge frequencies, fe, of DRs estimated using four methods: the TEN(HL) test; psychophysical tuning curves (PTCs) measured in simultaneous masking (320-Hz wide noise masker) using a 'fast' method (sweeping masker) and a 'classical' method; and PTCs measured in forward masking (sinusoidal masker) using a 'classical' method. Fourteen subjects with high-frequency DRs were tested. For measurement of PTCs, the signal frequency was chosen to fall inside the DR; the tip frequencies of the PTCs were taken as indicating the values of fe. The values of fe obtained from the PTCs in forward and simultaneous masking (both fast and classical methods) were similar and were usually close to, but somewhat above, the values of fe estimated from the TEN(HL) test. Fast PTCs measured in simultaneous masking are recommended for use in clinical practice, as they give a precise estimate of fe and are quick to administer.