Prophantasia is voluntary, and people not only control it, but as other comments point out, it feels like ‘self’. My brother, a PhD psychologist, has developed an interest in aphantasia. Aphantasics rarely hallucinate. So, from talking with him, we have a pretty good working hypothesis that schizoaffective disorder affects the same brain pathways as prophantasia, i.e. hallucinations that are not under voluntary or conscious control. (As an interesting side note, in highly-individualistic cultures, the voices and images more often feel malevolent and ‘other’ to sufferers, in contrast to people in collectivist cultures, who experience them more often as friendly and familial. It’s not necessarily maladaptive.)