Listening effort during speech in noise recognition: a neurophysiologic evaluation of consecutive sound processors

The technological development in the cochlear implants (CI) has been producing external processors designed to increase performances in patients facing word in noise recognition conditions. In our study we investigated the neurophysiological responses underlying these abilities, firstly aiming at obtaining an electroencephalographic (EEG) measure of the listening effort experienced by patients. Secondly, we investigated whether the technological progress reduced such listening effort levels in these patients. In parallel to this neurophysiological assessment, also behavioral performances have been evaluated, in order to test the eventual influence of different processors on the outcome of the task execution, that is word in noise recognition task. EEG Theta and Alpha rhythms activity has been estimated in Unilateral CI users undergoing word recognition test in the cocktail party background noise with a signal to noise ratio + 10, when employing four consecutive generations of CI sound processors, using or not the noisereduction filter function. Results showed that from an older processor to a more recent one, an increase in the speech discrimination has been observed, above all in the filtered condition. Comparing the conditions with and without the noisereduction filter, the latter one reported an increase in the EEG Alpha and Theta activity, especially for the two more recent processors. In the comparison between the different generations of sound processors the newer models reported the lowest levels of cognitive effort, as indicated by the lower values of Theta activity. These considerations support the usefulness of the employment of such EEG estimations for the assessment of clinical devices development. The present results also showed that technological evolution improved speech discrimination in noise, reducing the cognitive effort.