ON THE ORIGIN OF THE ENLARGED MELODIC OCTAVE

The perceptual octave is larger than the physical octave, i.e., most l isteners perceive that two tones are an octave apart when their freque ncy ratio is greater than 2. This result is known as the octave enlarg ement effect. There are two theories for the effect, one of them a cen tral template theory, the other a peripheral timing theory. In princip le, it is possible to determine which theory is better by discovering whether or not octave enlargement occurs for centrally generated dicho tic pitches such as the Huggins pitch. Experiments show that octave en largement does indeed occur for Huggins pitch. This is the result pred icted by the central template theory, but it can be argued that the re sult does not entirely eliminate the timing theory. A detailed examina tion of the two theories shows that each requires revision in order to make the octave enlargement prediction follow logically from its prem ises. The central template theory requires the auditory system to diff erentiate excitation caused by different harmonics of a complex tone o n some basis other than place of excitation. Neural synchrony is sugge sted as a basis. The timing theory, originally formulated in terms of a neural interspike interval timing, can be made internally consistent by replacing the neural interspike-interval circuit by a neural autoc orrelator.