Frequency Discrimination of Pulsed Tones

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Abstract
If a 2200-cps tone is pulsed 150 times/sec under appropriate conditions, a low pitch (periodicity pitch) is heard corresponding to that of a 150-cps tone, although there is little or no energy present at 150 cps in the signal. To account for the perception of this low pitch, it has been postulated that either the cochlea acts as a mechanical envelope "detector" resulting in neural activity in a peripheral "low-frequency or pitch" channel, or the cochlea performs a Fourier-like analysis resulting in neural activity in a peripheral "high-frequency or pitch" channel with this neural activity undergoing a central temporal analysis where the low periodicity pitch is "detected." Absolute threshold measures were obtained for three stimuli: a 2200-cps sinusoid, a 105-cps sinusoid, and a 2200-cps tone pulsed 150 times/sec. Frequency discrimination measures were obtained for the same three stimuli at various sensation levels. The measures obtained for the pulses were compared, by analysis of variance and correlation techniques, to those measures for each of the sinusoids. The cochlear detection hypothesis would demand a close relation between the pulse and 150-cps measures; none was found. Conversely, the central detection hypothesis would demand a closer relation between the pulse and 2200-cps measures; this was found. Furthermore, a lack of montonic relation between perceived pitch and repetition rate and a large "atonal range" was found for the pulses, indicating their perception involved mechanisms not involved in the perception of the sinusoidal stimuli, i.e., a central temporal analysis.

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