Spectral shape discrimination of two-tone complexes

Adaptive, 3-interval, 3-alternative forced-choice discrimination experiments were performed for changes in the amplitude of single elements that composed two-tone complexes. We utilized two-tone complexes of fixed frequency difference or fixed frequency ratio for each of several center frequencies. Experiments were carried out while roving overall stimulus intensity within and across trials. Sensitivity measured with two-tone complexes with a fixed frequency difference of 60 Hz reached a minimum of 0.5 dB for center frequencies near 1 kHz. In contrast, sensitivity measured with a fixed frequency ratio of 1.059 remained fairly invariant with changes of the center frequency. In general the results suggest that the auditory system performs an across-channel spectral profile analysis. Some of the results appear unexplainable by existing models, including the envelope-weighted averaged instantaneous frequency (EWAIF) model, which has explained many of such data in the past