Perception of harmonic intervals made by simultaneous complex tones

Most studies on pitch perception for complex tones deal with either isolated sounds (pitch matches) or with sequential pairs of such sounds (jnd or melodic interval experiments). Little attention has been given to the question how the auditory system perceives a sound of two or more simultaneous complex tones. Informal observation of musical behavior shows that if a chord, triad, or harmonic interval is played by a group of musical instruments, the various notes usually retain their identity in the perceived sound image. This poses the question how the auditory system parses and groups the spectral components of the total sound in order to compute the correct (simultaneous) pitches. An experiment was performed in which musically trained listeners were asked to identify harmonic intervals made up of two simultaneous complex tones, each comprising three successive random harmonics, by playing the intervals back on a keyboard. Tones were presented both diotically (all six spectral components to both ears) and dichotically (one three-tone complex to each ear). Data show that under most conditions e.g., most of the dichotic ones, the task can be done very well, but that diotic performance depends strongly on details of the total spectral pattern. This suggests that peripheral spectrum and central spectrum impose separate constraints on musical processing of complex sounds.