Electrophysiological correlate of masking release using a high-density EEG system.

Description

A fundamental processing principle of the auditory system of many mammals is to analyze sounds in separate frequency channels. This frequency specific processing allows to detect narrow-band signals in the presence of broadband maskers. As a conceptual model, a neurally coded “internal signal-to-noise ratio (I-SNR)” has been suggested which reflects the energy of the signal to be detected relative to the energy of the masker. This I-SNR is then related to the minimum required energy of the signal in order to be detected, i.e. the detection threshold. Perceptually, the detection threshold can be varied by inclusion of beneficial signal properties (cues) like comodulation or interaural disparities, leading to a a reduced detection threshold, i.e. a release from masking. In the light of the I-SNR, a masking release is then equivalent to an improvement of the I-SNR due to the presence of the cues in the signal. It is largely unknown how masked signals are represented in the neural system. Such an objective metric would however be beneficial for, among others, clinical applications to evaluate supra-threshold hearing in non-responding listeners. A few studies exist, trying to link long-latency auditory evoked potentials (LAEPs) with the threshold of a masked signal, finding a correlation between the P2 peak of the LAEP and the level of the signal above masked threshold. These studies focused on single channels to evaluate the LAEP which potentially obscures the information about the contribution of different nuclei to the masking release in the presence of multiple cues. Hence, recordings with a high-density EEG might help to provide spatially high sampled data to obtain information about the underlying processing stages. The present project will integrate a 144-channel EEG system (g.Tec) into the existing lab infrastructure of the Hearing systems group. The system will be evaluated with replication and extension of a previous study about the presence of masking release in LAEPs (Egger et al., in prep). Project outcomes The goal of the present project is twofold: a) implementation of a 144-channel EEG system into a measurement routine for LAEPs within the existing infrastructure and b) recording and processing of LAEPs recorded in response to stimuli known to evoke a masking release in multiple channels using available and custom software implemented in MATLAB. The developed system and software will be documented in written form. The developed code will be developed using GIT and published in an online repository (BitBucket), available for the Hearing Systems group at DTU.

Period	7 Aug 2017 → 10 Sept 2017