Pitch: The Perceptual Ends of the Periodicity; but Of What Periodicity?

The model for pitch assumes that pitch is based on the periodicity in the neural activities after the cochlear filtering. One could argue that the auditory system "uses" the pitch as cue for stream segregation. A question, however, would whether pitch is a cause or an end of such grouping. We investigated the case where two pulse trains with an identical periodicity are added with variable temporal disparities. The second pulse train with the identical IPI was added with various phase delays. When the phase delay was 50 %, the pitch raised by an octave. This impression of the octave shift appeared to be continuous as a function of the degree of the phase delay except for a hump was observed at 25 % point. The auditory model could not provide any corresponding peak in the time interval histogram of the neural activities. Another series of experiments by the authors indicated that aged absolute pitch possessors tended to perceive pitches higher than young AP possessors. An additional experiment using experimental sounds indicated that similar results could be obtained only for sounds having temporal information in the lower order region.