What or who are the voices in Jessie's head in the novel, Gerald’s Game?

As Jessie struggles with her memories and her fear, voices in her head narrate her pragmatism, her terror, and her lost innocence. In time they become characterized as Ruth Neary, a cynical college friend that Jessie admires, who enacted the social and emotional freedom Jessie craves; as Goody Burlingame, that part of her that is the traditional good wife, submitting to her husband in all things; and as Punkin, the intelligent, hopeful child.

While this could be confused with multiple personality disorder, these voices are not dissociated selves. Rather, her memory and imagination intensify her coping strategy of talking to herself throughout the ordeal.