I would say `narrator voice` in this context is distinctly different from internal dialogue. Obviously the internal voice can narrate to yourself, but that voice tends to be slightly different in my experience.

Narrator voice is a specific voice, cadence, pattern etc. that your internal voice takes on when reading a narrative, rather than the narration of your experience. For me, I have a different voice when reading/writing technical documentation compared to reading/writing fictional works, which both are different from my day to day internal dialogue.

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