The role of loudness perception in hearing aid fitting Temporal, spectral and binaural effects

One of the main aims in individual hearing aid fitting is to restore loudness perception with hearing aids close to normal based on hearing aid prescription rules.
In current hearing aid prescription rules loudness normalization is based on historic loudness data or on loudness models. Three limitations of this approach are addressed in this thesis. The first limitation is that the loudness data which form the basis of the prescription rules have been collected with static stimuli. However, as shown in this thesis, the loudness of dynamic stimuli is not well predicted by these models.
The second limitation is that hearing aid prescription rules are threshold based. But in this thesis is shown that, thresholds are a very poor predictor of the loudness function, and individual differences are large.
Finally, hearing aid prescription rules assume that spectral and binaural loudness summation are reduced by hearing loss, and are not significantly affected by loudness normalization. In hearing-impaired listeners with different degrees of symmetrical hearing losses the effect of loudness normalization was studied. It was shown that for larger hearing losses spectral and binaural loudness summation usually is much larger than for normal hearing listeners, especially for broadband signals.
It was also shown that without loudness normalization in bilaterally presented signals the lower frequency part of the signal had a larger contribution to the overall loudness perception than the higher frequency part.
To optimize hearing aid fitting, individual loudness measurements are recommended, including loudness measurements of broadband signals.