ANR - LEAP

Memory and perception must be closely linked for hearing. Imagine trying to follow an animated conversation in a busy restaurant. Being able to detect changes from the ongoing context is a useful skill, to realize that a new talker has just joined in. Another useful skill is being able to recognize the voice of a given individual, to understand who just said what. Unfortunately, we do not know how these memory-like processes operate, or even on which acoustic features they depend. This is a major hole in our fundamental understanding of auditory perception. It is also likely to be a stumbling block in a clinical perspective, as people suffering from hearing impairment typically have problems in auditory scenes resembling the one we have just described.

This project is concerned with understanding what kind of acoustic changes the auditory system can enhance in the short term, and how perceptual memories are formed in the longer term. Both issues will be addressed with the hypothesis that implicit memory processes may be involved. We will first investigate these issues psychophysically and then investigate the neural correlates of enhancement and perceptual memory using electro-encephalography. Finally, we will evaluate how hearing impairment impacts both enhancement and perceptual memory.

There are not many psychophysical investigations of auditory memory using complex sounds that are not speech. This contrasts with the recent series of discoveries made in auditory physiology. For instance, rapid plasticity has been demonstrated in the auditory cortex. Neural adaptive coding has also been observed, starting from the auditory periphery. The behavioral consequences of these potentially useful neural mechanisms still need to be addressed. This is one of the aims of the project, to renew the psychophysical approaches of auditory memory and context effects in the light of recent neurophysiological data.

The project is also motivated by the opportunity to develop recent and potentially important findings by each of the two academic partners. The partner team led by Laurent Demany in Bordeaux has shown that listeners were able to reliably detect changes in frequency between two tones, even when one of them was not consciously perceived. This has led to the hypothesis that an implicit memory was available to monitor changes in complex auditory scenes. The project will investigate whether other kinds of acoustic changes can be enhanced by implicit memory. The partner team led by Daniel Pressnitzer has discovered that listeners were surprisingly able to learn highly complex sounds in a fast, robust, and long-lasting manner. As learning occurred even though listeners were not actively trying to memorize sounds, this again suggested an implicit mechanism. The project will build on the new psychophysical paradigm now available to observe the formation of auditory memories, in order to investigate the features which are crucial for the learning of complex sounds.

A further motivation is to translate these fundamental advances to clinical research on hearing impairment. The third partner of the project, Entendre SAS, is a nationwide network of audiologists. Under the scientific supervision of Stéphane Garnier, this partnership will ensure that the project has the best possible chance to provide tangible benefits for audiologists and patients.

Finally, the consortium is well-suited for a focused investigation. All three partners have a recent track record of collaboration, even though they have not yet been funded on a common grant. Projects on auditory change-detection have already produced peer-reviewed publications in common from the two academic teams (2 in 2009, 2 in revision, 1 submitted). The industrial partner has a history of collaboration with one of the academic team, also with common publications (3 in 3 years). All this should ensure that the project develops in a timely and efficient manner.