Le jeudi 22 mars 2007, de 10h à 11h, à l'ENS, 45 rue d'Ulm, salle des Actes.
Pr David
McAlpine, directeur du Ear
Institute, University College London.
The representation of auditory space in the human brain.
Humans make use of small differences in the timing of a sound at the two
ears to determine the location of the sound source. For 60 years the major
model developed to understand how the brain encodes these interaural time
differences (ITDs) has consisted of an array of coincidence detectors
innervated by series of delay lines. The purpose of this arrangement is to
translate information about the timing of a sound at each ear into a place
code - a position within an array of neurons tuned to a specific ITD and, by
extension, a position in auditory space. Here, I present neurophysiological
evidence from the mammalian brain indicating that this model can no longer
hold. Using in vivo electrophysiology in small mammals, functional MRI
scanning in the human midbrain and recordings of the mismatch negativity
potential, I show that the brain's representation of ITD is in the form of a
distributed code, with no strict relationship between the side on which a
sound is perceived and the brain hemisphere activated. Depending on the
magnitude of the ITD, either the ipsilateral or contralateral midbrain and
cortex may be more active. These data indicate the need for a new model of
spatial hearing.
Ecole Normale Supérieure, 45 rue d'Ulm, 75005 Paris [plan]
[Equipe Audition]
[CNRS]
[LPP Paris 5]
[ENS]
[DEC]
