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Laboratory of Auditory Neurophysiology

Our overall objective is an understanding of brain mechanisms underlying human hearing. Hearing differs from the other senses in being based on extremely fast neural processes, and our focus is on these temporal processes in the initial stages of the auditory system. We strive to understand neural computations performed by small circuits.

In contrast to the receptor organs for vision and touch, the inner ear does not have an explicit representation of space. All auditory information is contained in pressure fluctuations as a function of time at the two eardrums. The inner ear performs a frequency analysis rather than a spatial analysis. The spatial position of a sound source is computed in the central nervous system from implicit information sent downstream by the inner ear, and involves comparisons between the two ears. For humans, the most important source of information are tiny time differences between the acoustic waveforms reaching the two ears. For example, when a sound in the right speaker of a headset is switched on only fractions of a millisecond later than the speaker at the left ear, humans perceive this time difference as a shift in the position of the sound to the left ear. This is remarkable because the electrical signals by which neurons communicate are slow when compared to this submillisecond sensitivity. By recording electrical signals from the brain while manipulating the sounds to the two ears, we investigate how this extreme sensitivity to time differences comes about. Other fundamental features of auditory neural processing that we investigate are the frequency analysis in the inner ear; the coding of amplitude modulations; and the computation of differences in intensity between the two ears, which is another cue for the spatial localization of sounds.

The results from our research give a framework to understand clinical conditions in which temporal processes are disturbed. Furthermore, by investigating the processing of temporal information in the normal brain, we provide fundamental knowledge that is used in the design of artificial ears (cochlear implants) for the profoundly deaf.

The laboratory is in the department of neurosciences.