Robert S. Schlauch
Dept. of Commun. Disord., 115 Shevlin Hall, Univ. of Minnesota, Minneapolis, MN 55455
The relation between loudness and intensity discrimination was studied in three normally hearing listeners in quiet and in two levels of broadband noise. Intensity discrimination was measured for gated and continuous standards as a function of level. Loudness balances were obtained as a function of level as well. Forced-choice procedures were used for all measurements. Just-noticeable differences (jnd's) were elevated in noise conditions, relative to those in quiet, when comparisons were made for equal SPLs. Subjects showed loudness recruitment in the noise conditions. The framework for the models is an extension of the work reported by McGill and Goldberg [J. Acoust. Soc. Am. 44, 576--581 (1968)]. A model based on the subjective analog of Weber's law predicted smaller jnds in the shifted-threshold conditions than in quiet. By contrast, a neural counting model, based on the assumption that the neural noise that limits discrimination is related to the spontaneous firing of units not activated by the stimulus, predicts the correct relation for all conditions. The neural counting model also predicts Weber's law for intensity discrimination of broadband noise.