Models of the effects of threshold on loudness growth and summation

The present paper extends previous efforts to compare models of additivity of masking in normal and impaired listeners to measures of loudness. A model that provides a good account of additivity of masking for normal and impaired listeners, the modified power-law model with compressed internal noise, also provides a good description of basic loudness data from normal and impaired listeners. This model has been discussed frequently in the literature on loudness as one means of correcting loudness functions near threshold, but has not been widely accepted. The applicability of this model to loudness growth and the summation of loudness, both monaurally and binaurally, is evaluated and compared to the more generally accepted alternative. The ability of the model reported here to account for growth of loudness near threshold, as well as the additivity of masking, suggests a need to reconsider its application to loudness data, as well as a need to reconsider the relation between loudness and masking.