Profile analysis for irregular intensity spectra

Abstract

In our previous experiments with the simultaneous spectral discrimination process called profile analysis, we measured the just detectable increment in the center component of a multitone complex. In those experiments, the multitone background was uniform in level. The present paper describes the results from conditions where the center component of the complex (the one to which the signal was added) was varied in level relative to the other components, thus forming a “pedestal” on the other-wise flat spectrum. The pedestal was varied from 18 dB below to 24 dB above the level of the other background components. Four equilog multi-tone backgrounds were used consisting of 3, 5, 11, or 21 components including the pedestal component. The overall level of the sound was varied ± 20 dB within trials. The threshold of an increment in the middle component of the complex was measured as a function of the pedestal The resulting function had a rather broad, shallow “U” shape. The minimum in the function usually occurred at a small positive pedestal value. In keeping with our earlier findings, the more components in the background, the lower the increment threshold. An asymmetry was observed between positive and negative pedestal levels that may be attributed to masking. [Work supported by NIH.]