How we hear what is not there: A neural mechanism for the missing fundamental illusion

Dante R. Chialvo
2003 Chaos  
How the brain estimates the pitch of a complex sound remains unsolved. Complex sounds are composed of more than one tone. When two tones occur together, a third lower pitched tone is often heard. This is referred to as the "missing fundamental illusion" because the perceived pitch is a frequency ͑fundamental͒ for which there is no actual source vibration. This phenomenon exemplifies a larger variety of problems related to how pitch is extracted from complex tones, music and speech, and thus has
more » ... been extensively used to test theories of pitch perception. A noisy nonlinear process is presented here as a candidate neural mechanism to explain the majority of reported phenomenology and provide specific quantitative predictions. The two basic premises of this model are as follows: ͑I͒ The individual tones composing the complex tones add linearly producing peaks of constructive interference whose amplitude is always insufficient to fire the neuron ͑II͒: The spike threshold is reached only with noise, which naturally selects the maximum constructive interferences. The spacing of these maxima, and consequently the spikes, occurs at a rate identical to the perceived pitch for the complex tone. Comparison with psychophysical and physiological data reveals a remarkable quantitative agreement not dependent on adjustable parameters. In addition, results from numerical simulations across different models are consistent, suggesting relevance to other sensory modalities. When two tones occur together, such as in a complex sound, a third lower pitched tone is often heard. This is referred to as the "missing fundamental illusion" because the perceived pitch is a frequency "fundamental... for which there is no actual source vibration. How the brain estimates the pitch is a controversial issue which remains unsolved despite extensive work. A nonlinear model is proposed here in which a noisy detection produces neural spikes, occurring at a rate identical to the perceived pitch for the complex tone. The comparison with psychophysical and physiological data reveals a remarkable quantitative agreement not dependent on adjustable parameters. In addition, results from numerical simulations across different models are consistent, suggesting relevance to other sensory modalities. CHAOS VOLUME 13, NUMBER
doi:10.1063/1.1617771 pmid:14604413 fatcat:i2a5xrqztnguxbmmthwrdjrtm4