A computational loudness model for electric and acoustic stimulation based on peripheral neural activity

Loudness is a hearing perceptual feature related to how humans code the level of sounds. The overall neural activity at cortical levels is linearly related to the perception of loudness, however, this is not the case at more peripheral stages in the auditory pathway. In the peripheral auditory system, the amount of neural activity is related to physical features of the stimulus such as sound intensity and spectral content in acoustic stimulation, and current levels and excitation spread in electric stimulation with cochlear implants (CIs).

In an effort to understand how the peripheral neural activity relates to loudness, a computational model was designed to predict loudness perception from the spike activity produced by a peripheral auditory model for electric-acoustic stimulation (PAMEAS). The performance of the model was validated for electric stimulation only (ES) by reproducing experiments where the effect of stimulation rate, excitation spread and amplitude modulation were tested in CI users. The performance with acoustic stimulation only (AS) was compared to state-of-the-art models that predict loudness directly from the acoustic stimulus instead of the peripheral neural activity. The parameters of the loudness model were independent of the stimulation mode (ES or AS).The proposed model was capable to reproduce qualitatively the loudness perception of real CI users in ES experiments. It was also able to reproduce “in-between” representations of loudness as in state-of-the-art models for AS, i.e. excitation profile, specific loudness and instantaneous loudness.

This work provided a computational tool that makes a step towards closing the gap between simulations and a high level perceptual feature such as loudness. The most important characteristic is that it can be coupled to physiological models of the peripheral auditory system for electric and acoustic stimulation. Therefore, this work suggests that the mechanisms to recruit loudness in normal and electric hearing are similar after the peripheral stage.