Annie Moulin, Aurélie Bidet-Caulet, Perrine Ruby
The impact of top-down auditory attention on perception will be studied simultaneously on the different stages of auditory processing, from very peripheral mechanisms (cochlear responses), brainstem responses, up to cortical responses, explored by scalp EEG. To further understand the interaction between bottom-up and top-down mechanisms, we develop a new field of research on the auditory efferent system, that forms multiple cortical and subcortical loops, the most peripheral of which is represented by a brainstem loop that can directly modulate cochlear responses. This brainstem loop is the only one accessible for non-invasive exploration in humans and represents the necessary pathway by which higher centers can modulate cochlear responses. The primary role attributed to this efferent modulation is to dampen the cochlear gain in response to acoustic stimuli perceived as noise, i.e. irrelevant acoustic stimuli, by opposition to acoustic stimuli on which attention is focused, hence helping hearing in noise. The efficiency of this efferent pathway has been shown to be altered in speech language impairments, and can be improved by auditory training, with a correlation between the increase of the efferent control efficiency and the improvement observed in a task of speech perception in noise. Auditory efferent feedback is particularly high in musicians who tend to show remarkable hearing conservation considering the levels and prolonged exposure to music they undergo, suggesting the potential of musical training to improve auditory efferent efficiency.
Hence, by its focus on the influence of auditory selective attention at each stage of the auditory pathway, this project could lead not only to a way of diagnosing a lack of top-down control (which has been observed in several learning disorders) but also a way of training the auditory efferent system to improve top-down control, via auditory selective attention training. This has particular importance considering the recent evidence linking efficiency of top-down auditory efferent control with the susceptibility to hidden hearing-loss and cochlear ageing. Indeed, hidden hearing-loss is a relatively new concept, describing synaptopathy between neurosensory cells and auditory nerve fibers, attributed to moderate noise exposure and that manifests itself by specific difficulties in hearing in noise, with otherwise normal hearing. Unfortunately, several pathologies with different etiologies show an abnormal deficit in hearing in noise: from hidden hearing loss, peripheral hearing loss and presbycusis, up to auditory processing disorders. We plan to investigate the differences in hearing in noise difficulties according to the etiology of the deficits, which involves, first, constitution of a large database of normally hearing young adults, from which abnormal listening effort indexes will be defined, in order to identify hidden hearing losses.