Environmental statistics enable perceptual separation of sound and space

TitleEnvironmental statistics enable perceptual separation of sound and space
Publication TypeConference Abstract
Year of Publication2016
AuthorsTraer, J, McDermott, JH
Conference NameSpeech and Audio in the Northeast

The sound that reaches our ears from colliding objects (i.e. bouncing, scraping, rolling etc.) is structured, both by the physical characteristics of the sound source and by environmental reverberation. The inference of any one single parameter (mass, size, material, motion, room size, distance) is ill-posed, yet humans can simultaneously identify properties of sound sources and environments from the resulting sound, via mechanisms that remain unclear. We investigate whether our ability to recognize sound sources and spaces reflects an ability to separately infer how physical factors effect sound, and whether any such separation is enabled by statistical regularities of real-world sounds and real-world reverberation. To first determine whether such statistical regularities exist, we measured impulse responses (IRs) of both solid objects and environmental spaces sampled from the distribution encountered by humans during daily life. Both the objects and the sampled spaces were diverse, but their IRs were tightly constrained, exhibiting exponential decay at frequency-dependent rates.  Object IRs showed sharp spectral peaks due to strong resonances and environmental IRs showed broad frequency variation: mid frequencies reverberated longest while higher and lower frequencies decayed more rapidly, presumably due to absorptive properties of materials and air. To test whether humans utilize these regularities to separate reverberation from sources, we manipulated environmental IR characteristics in simulated reverberant audio. Listeners could discriminate sound sources and environments from these signals, but we found that their abilities degraded when reverberation characteristics deviated from those of real-world environments. Subjectively, atypical IRs were mistaken for sound sources. The results suggest the brain separates sound into contributions from the source and the environment, constrained by a prior on natural reverberation. This separation process may contribute to robust recognition while providing information about spaces around us.

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