Human-Like Modulation Sensitivity Emerging through Optimization to Natural Sound Recognition

Natural sounds contain rich patterns of amplitude modulation (AM), which is one of the essential sound dimensions for au-ditory perception. The sensitivity of human hearing to AM measured by psychophysics takes diverse forms depending on the experimental conditions. Here, we address with a single framework the questions of why such patterns of AM sensitivity have emerged in the human auditory system and how they are realized by our neural mechanisms. Assuming that optimiza-tion for natural sound recognition has taken place during human evolution and development, we examined its effect on the formation of AM sensitivity by optimizing a computational model, specifically, a multilayer neural network, for natural sound (namely, everyday sounds and speech sounds) recognition and simulating psychophysical experiments in which the AM sensi-tivity of the model was assessed. Relatively higher layers in the model optimized to sounds with natural AM statistics exhib-ited AM sensitivity similar to that of humans, although the model was not designed to reproduce human-like AM sensitivity. Moreover, simulated neurophysiological experiments on the model revealed a correspondence between the model layers and the auditory brain regions. The layers in which human-like psychophysical AM sensitivity emerged exhibited substantial neu-rophysiological similarity with the auditory midbrain and higher regions. These results suggest that human behavioral AM sensitivity has emerged as a result of optimization for natural sound recognition in the course of our evolution and/or devel-opment and that it is based on a stimulus representation encoded in the neural firing rates in the auditory midbrain and higher regions.

Automated summary

By using a computational model, researchers found that human sensitivity to amplitude modulation in natural sounds may have emerged as a result of optimization for natural sound recognition and it is associated with neurophysiological similarity in the auditory brain regions.