Pick out the odd one

Work of _______ gives the correct and same size of the object.

With the help of electricity ______ helps to increase the pitch of the sound.

____________prevents sound impulses from reaching the brain while we are sleeping.

Sound waves enter the ear and vibrate the:

Eye - vision;           Ear - ?

__________is an equipment to help the blind.

Loud speaker - Sound pollution;  Plastic - ?

Which one is the function of an ear?