Nowadays, cochlear implants (CI) are successfully used to rehabilitate severe to profound sensorineural hearing loss. Most CI users can understand speech in quiet, but comprehension scores drop in the presence of background noise and in adverse conditions. Listening with a cochlear implant remains very demanding and most listeners report high levels of listening effort. The aim of current auditory prostheses and cochlear implants is not only restore speech understanding, but also to restore all the cognitive functions that are associated to a listening task (e.g., memory, executive functions, attention). Evaluating the listening effort is a new way to assess the efficiency of the hearing aids or cochlear implants. The listening effort indicates the amount of cognitive resources that are dedicated to a listening task; it evaluates also the cognitive resources remaining available for the other cognitive functions. The present study is a "pilot" aiming to evaluate listening effort for cochlear implant users. The listening effort is measured with pupillometry, i. e. by measuring the pupil dilatation in response to different stimuli. The size of the pupil is known to increase with the listening effort. The listening effort is evaluated in two different situation: speech perception in quiet and speech perception in noise. Speech comprehension is measured for the two listening conditions and cognitive functions are assessed by the MOCA (Montreal Cognitive Assessment). In addition, the subjects are asked to subjectively evaluate the amount of listening effort they used in each listening situation. The pupillometry measures will be compared for the two listening conditions. Moreover, the study will evaluate the relationship between objective (pupil dilatation) and subjective measures (self evaluation) of listening effort, and between speech comprehension, cognitive abilities and listening effort.