Analysis of a forward masking paradigm proposed to estimate cochlear compression using an auditory nerve model and signal detection theory

The healthy human auditory system has a large dynamic range. An “active mechanism”, presumably due to the electromotility of the outer hair cells in the cochlea, leads to level-dependent amplification of basilar membrane (BM) vibration and a compressive BM input/output function. Different methods for estimating this compressive function based on behavioural forward masking have been suggested. These methods are based on the assumption that BM processing can be isolated from the response of the overall system and that the forward masking onto the probe is different for on- and off-frequency maskers. In the present study, a computational model of the auditory nerve (AN) in combination with methods from signal detection theory was used to test these assumptions. The simulated AN response was quantified in terms of rate and synchrony for different AN fibre types. Contribution of different tonotopic regions to overall sensitivity to the stimuli were analysed. The results show that on- and off-frequency maskers produce similar forward masking onto the probe. The simulation results suggest that the estimate of compression based on the behavioural experiment cannot be derived from sensitivity at the level of the AN but requires additional contributions, consistent with physiological studies.