‘Frequency’ and the Detection of Spectral Shape Change

Abstract

In several recent papers, we have investigated the detection of a change in spectral shape of a complex auditory signal. The discrimination task involves a broadband ‘standard’ spectrum and some alteration of that spectrum produced by adding a ‘signal’ to the standard. For most of the experiments, we have used a standard that is composed of a set of equal- amplitude sinusoidal components. The standard spectrum is, therefore, essentially flat. In different experiments, different waveforms have been added to this standard spectrum to create a change in spectral shape, and the detectability of such changes has been measured. A signal commonly used in these experiments was a single sinusoid added in-phase to some component of the standard. Since this signal increases the intensity at only one frequency region, we describe this situation as detecting a ‘bump’ in an otherwise flat spectrum. One experimental question is whether a bump at one frequency region is easier to hear than a bump at some different frequency region. Also, we might consider more complicated changes in the spectra such as a signal that produces changes in the amplitudes of several components of the standard. How well are such alterations of the acoustic spectra detected, and how is the detectability of these general changes related to the detectability of an increment at one frequency?