The Cocktail party filter: how the brain enhances auditory signal contrasts
Holger Schulze and his team found a surprising answer: the auditory system can discriminate voices according to their time structure. Only signals from the chosen voice will be processed, while processing of all the other voices is inhibited: the winner takes it all.
Everybody who attends a cocktail party from time to time might have realized the amazing ability of our auditory system to be able to listen to and understand somebody speaking while many other people are talking loudly at the same time. This so-called “cocktail party phenomenon” is based on the ability of the human auditory system to decompose the acoustic world into discrete objects of perception. It was originally believed that the major acoustic cue the auditory system uses to solve this task is directional information of the sound source, but even though localisation of different sound sources with two ears improves the performance, it can be achieved monaurally, for example in telephone conversations, where no directional information is available.
Scientists from the Leibniz-Institute for Neurobiology in Magdeburg, and the Universities of Ulm, Newcastle and Erlangen, have now found a neuronal mechanism in the auditory system that is able to solve the task based on the analysis of the temporal fine structure of the acoustic scene. The idea is that different speakers have different temporal fine structures in their voiced speech and that such signals are represented in different areas of the auditory cortex according to this different time structure. By means of a so-called “winner-take-all” algorithm one of these representations then gains control over all other representations.
The result of this mechanism is that only the voice of the speaker you want to listen to is still represented in auditory cortex and can therefore be followed over time. This predominance of the representation of one speaker's voice over the representations of all other speakers is achieved by long-range inhibitory interactions that are first described by the paper of Kurt et al. by means of functional neurophysiological, pharmacological and anatomical methods.
Their findings led us to a deeper understanding of how the parcellation of sensory input from perceptually distinct objects is realised in the brain, and may, for example, help to improve hearing aids for which cocktail party-like situations are still a major problem.
Press release to accompany the article “Auditory Cortical Contrast Enhancing by Global Winner-Take-All Inhibitory Interactions” by Simone Kurt, Anke Deutscher, John M. Crook, Frank W. Ohl, Eike Budinger, Christoph K. Moeller, Henning Scheich, and Holger Schulze to appear in PLoS ONE on Wednesday, March 5.
Prof. Dr. Holger Schulze
University of Erlangen-Nuremberg
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