[david_ar]

In some sense you could say the vast majority of people hear voices, it's just that we conceptualise this as the "inner voice". It seems somewhat plausible that people could conceptualise this differently if there were a sufficiently strong cultural pressure. Perhaps when we hear words in our heads that we describe as talking to ourselves, ancient people would describe the same experience as gods speaking to them?

[phylomortis]

Not only ancient people. The concept of a “foreign” inner voice exists in islam and is called vesvese in Turkish. It is commonly attributed to being deceit from satan and as a child you get taught to actively repress it.

[posterboy]

I tried to record myself, to capture my inner monologue, and found it really painful to listen to. I'm also not very good at role play or impersonation. But a professional performer, like a priest or entertainer, has to do it more than just habitually, and their manners become adapted and people might affect a whole dialectic. Whereas children rather randomly babel and come up with unique manerism that are uncommon and consequently deemed unfit. Further, if you grant that deus ex machina could be a bodyless voice in plays and earlier temple ceremonies, it stands to reason that people would consequently spin these messages further and reanalyse their inner monologue as word of god, not the least to shift responsibility, e.g. to the uber-ich, in Freud's terms.