Projects

Harmonicity in auditory perception

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When objects in the world vibrate, pressure changes in the form of acoustical waves are propagated through air. The auditory system evolved to infer information about the environment from these waves. Audition is a fundamental sense for humans, as it enables verbal communication and helps with orientation in the world. Although data provided by the hearing apparatus is relatively sparse (in essence, two highly correlated signals), the brain is able to infer surprising amounts of information from this data. Many recent studies suggest that this inference is possible because the brain forms top-down predictions about the incoming auditory stimuli and their causes. These predictions are formed using an internal, generative model that is constantly updated by statistical regularities in the incoming sensory data. A ‘surprise’ response (or prediction error) is generated when predictions do not fit the sensory data and is used to update the contents of the internal model. These ‘surprise’ responses in the auditory system are seen as primary sources of mismatch responses (for example the mismatch negativity, MMN) recorded with electroencephalography (EEG). Crucially, it is assumed that these responses are stronger for more reliable stimuli.

Many sounds in the environment are harmonic complex tones comprised of a fundamental frequency (F0) and a set of frequencies that are integer multiples (harmonics) of that fundamental. Many of these sounds in nature are formed by resonating objects, as is the case in human and animal voices or musical instruments. Conversely, inharmonic sounds have various deviations from the harmonic series. Previous studies have shown that highly harmonic signals tend to produce a more salient pitch sensation, pitch comparisons are easier for harmonic signals and violations of harmonicity impair the intelligibility of concurrent utterances of speech. In this project, we propose that harmonicity can be seen as a basic statistical regularity in the auditory domain that serves as an index of precision. In a series of experiments, we will investigate electrophysiological responses of the brain to harmonic and inharmonic sounds in the form of event-related potentials (ERPs).

The results of the proposed project will contribute to the scientific understanding of how the brain is encoding uncertainty on very small timescales required for auditory perception. This is one of the central questions in the science of perception and in neuroscience in general. Results will also contribute to the understanding of pitch perception - a process critical for language, music and other auditory processes.

External collaborators

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Alejandro Blenkmann, University of Oslo

David R. Quiroga-Martinez, UC Berkeley

Funding

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NCN SONATA 2022/47/D/HS6/03323