Periodicity and pitch perception.

There has been experimental evidence pointing to at least two pitch mechanisms, the first involving low-order harmonics that are resolved along the basilar membrane, and the second a periodicity mechanism that depends only on the repetition rate of the time waveform on the basilar membrane. If this time waveform is derived from repeated bursts of sinusoidal tone, the second mechanism might be the sole pitch mechanism. It is found that this can be so up to rates as high as 250 bursts of 4978-Hz tone per second. The stimuli used are periodic patterns of equally spaced tone bursts, with either successive tone bursts in the same phase, or every fourth tone burst 180 degrees out of phase with respect to the rest. Up to a critical transitional rate of tone bursts a second, the two sequences sound exactly the same, despite their different fundamental frequencies and frequency separation of harmonics. Critical rate data are given for sinusoidal bursts of seven different frequencies. Critical rates appear to be closely related to the critical bandwidth. Pitch matching appears to be consistent with these observations; it is on rate below the critical rate and can be on fundamental frequency above the critical rate.