Why do singers such as Mariah Carey put a finger in their ear before hitting a high note?

There seem to be several reasons for this practise:

- because one ear exposed to the high levels of noise is better than two ears exposed

- so they can hear the music internally and to focus on the key

- the finger on the ear can signal the Monitor Engineer to turn up the volume to the person's In-Ear Monitor system

- Another reason is that it is loud onstage, and sometimes the monitors (the speakers on stage providing the band's sound to the singer) can be over powered by the sound of the band. One way to combat this is to put a finger in your ear and hear your voice vibrate through your head - as opposed to hearing it come out of your mouth.