Context effects in sound intensity encoding and perception

Abstract: Animal studies have shown that auditory neurons adapt their firing rate depending on the sound level statistics of the stimulation. This Dynamic Range Adaptation (DRA) has been measured by presenting short segments of noise or tones with some levels presented more than others. DRA manifests as a shift of the rate-level function towards the most presented levels, and produces a change in sensitivity enhancing the coding of these levels. DRA has been observed in the inferior colliculus and in the auditory nerve (AN), implying that the hair cells, the hair cell-AN synapses and/or the AN contribute to this phenomenon.

The first aim of this thesis was to find a perceptual correlate of DRA in normal-hearing participants. We measured intensity discrimination for pure-tone and broadband-noise test signals embedded in different contexts with the hypothesis that discrimination thresholds should be lower when the context mean level matches the test signal level. For broadband signals, the results were fully consistent with this hypothesis while for pure tones, intensity discrimination always degraded with increases in context level, independently from the test levels.
The second aim was to test whether the AN directly contributes to DRA. We measured electrically-evoked compound action potential responses to electrical stimulus sequences with specific level distributions in cochlear implant listeners, for whom the hair cells and hair cell-AN synapses are bypassed. Electrically stimulated AN fibers collectively exhibit a behavior consistent with DRA, demonstrating that the AN contributes to DRA. 

Jury

• Laurel H. CARNEY Rapporteure (Prof., University of Rochester)
• Etienne GAUDRAIN Rapporteur (Chargé de Recherche, CNRS, Centre de Recherche en Neurosciences)
• Emmanuel PONSOT Examinateur (Chargé de Recherche, CNRS, IRCAM, Laboratoire STMS)
• Christian LORENZI Examinateur (Prof., ENS Paris)
• Sabine MEUNIER Directrice de thèse (Chargée de Recherche, CNRS, LMA)
• Olivier MACHEREY Directeur de thèse (Directeur de Recherche, CNRS, LMA)

La soutenance de thèse de Coline Marché est prévue le 6 mai à 14h00 - amphithéâtre du LMA