EEG variations as estimators of listening effort during recognition of words in noise in unilateral and bilateral sequential adult cochlear implant users.

The listening effort, defined as "the mental exertion required to attend to, and understand, an auditory message" [McGarrigle et al 2014] is a matter receiving wide interest in the scientific community. In particular the challenge is its evaluation beyond the self-report data obtained through questionnaires or individuals' verbal reports. Multiple evidences highlight a role for posterior Alpha and frontal Theta EEG rhythms variation for the estimation of the listening effort, implying an inhibitory activity toward irrelevant/distracting stimuli for Alpha, while working memory and lexico-semantic processing for Theta [Strauß et al 2014; Wisniewski et al 2015]. The evaluation of the listening effort appears extremely worthy in hearing impaired patients, since the presence of noise or distortions in a speech signal increases cognitive demand and listening effort [Stenfelt & Rönnberg 2009]. In addition, such evaluation it would be interesting to be investigated comparing the unilateral CI with the bilateral CI condition, since the availability of more auditory information in the second one. The balance between Theta and Alpha EEG rhythms seems essential for the word recognition. Therefore aim of the present study was the assessment of the listening effort during a word in noise recognition task in CI adult users before and after the implantation of the second CI. Present results evidenced an increase in the frontal Theta and parietal Alpha for a quite difficult noise condition, and for Theta in correspondence of the stimulus. Moreover, frontal Theta activity increased along the task for the same difficult noise condition during and after the stimulus. These considerations appears useful for the neurophysiological characterization of CI users in order of further applications toward the management of cognitive resources and tailor-made rehabilitations.