Voices are different sides of one's self (it is in one's head no one else can get in there?) but some people do not experience them as such, experience them as coming from something other than in their lives or selves and their lack of self esteem, etc. (can't lack self worth or you would not bother struggling to get better and have a better life experience, there'd be no point if you are worthless.). Tell the doctor/therapists about the voices in your head and what they say, etc. and how you view them, that's all that matters, not that there are "voices" or not.

My therapist told me to tell mine that she did not believe they existed and how convoluted that was and what I pictured in my mind (she was a small oriental woman, they were big male-seeming voices) when I thought about telling "them" that (like a cartoon cat fight with dust obscuring what was happening, just legs and arms showing but her "winning") made me laugh and they "went away" from then on.

To battle the self-esteem voices whenever I caught myself putting myself down in my head or out loud/voicing it, I would yell "Support!" in my head and three little guys in togas carrying a Corinthian column would run in from one ear and put it up in the "dome" of my head and then run out the other ear and that got the message across to me that I was more clever and more fun (if nothing else? :-) than the negative voices.