Pitch of amplitude-modulated low-pass noise and predictions by temporal and spectral theories

Pitch phenomena related to the periodic interruption rate of white noise have traditionally been regarded as evidence for time domain pitch processing in the auditory system since spectra of these signals are flat. Short-term spectra, however, contain information about the interruption rate. Melodic interval identification experiments were performed with sounds comprising low-pass filtered noise modulated by either a sine wave, a square wave, or a periodic narrow pulse wave. Melodic intervals were generated by varying the modulation frequency fm while the low-pass cutoff frequency fco of the noise was an experimental variable. The correct identification score shows a particular dependence on the ratio fco/fm for each type of modulation signal. Shapes and relative positions of performance functions are compared with predictions derived from an energy detector (time domain) model and a short-term power spectrum correlation (frequency domain) model, and are found to support the former more strongly than the latter. There is some evidence, however, for the existence of both types of processing in the auditory system.