The results of the previous study on auditory effort in young children with cochlear implants show that pupils respond to the presence or the absence of the perceived stimuli. The investigators hypothesize that the perceived sounds will elicit increased pupil dilation compared to the non-perceived sounds and that the hearing threshold as measured with pure tone audiometry will correlate to the results in pupillometry test. The investigators hypothesize that the effect will be visible in all testing groups albeit the relative increase of pupil size with age. Hypothesis confirmed, the investigators will develop a standardised procedure for the auditory signal detection using pupillometry. Such a procedure could represent an important bridge between automatic and behavioral hearing tests. With a more precise test of auditory threshold of young children, post-operative monitoring and fitting of cochlear implants or hearing aids, and rehabilitation procedures, could be considerably more targeted and consequentially more efficient.

Inclusion Criteria:

• Normal or corrected-to-normal vision
• No history of relevant neurological or psychiatric concomitant disease
• Age: 4-36 months
• At least 1 months of more after initial fitting of the CI or hearing aid (only for aided subjects)

Exclusion Criteria:

• Developmental disorders
• Unwillingness of the subject to participate further

Participants with and without hearing impairment