Her life was purportedly described, with adaptations to protect her anonymity, in 1973 in the book Sybil, subtitled The True Story of a Woman Possessed by 16 Separate Personalities.

In regard to Mason's mother: "...many people in Dodge Center say Mattie" — "Hattie" in the book — "was bizarre," according to Bettie Borst Christensen, who grew up across the street.

She had long suffered from blackouts and emotional breakdowns, and finally entered psychotherapy with Cornelia B. Wilbur, a Freudian psychiatrist.

[3] Over one hundred paintings were found locked in a closet in Mason's Lexington home when it was being emptied after her estate sale.

[7] Schreiber's book, whose veracity was challenged (e.g., Sybil Exposed by Debbie Nathan[8]), stated that Mason had multiple personalities as a result of severe child sexual abuse at the hands of her mother, who, Wilbur believed, had schizophrenia.

[9] The book was made into a highly acclaimed TV movie, starring Sally Field and Joanne Woodward, in 1976.

In fact, he later stated that Mason denied to him that she was "multiple" but claimed that Wilbur wanted her to exhibit other personalities.

[11] Spiegel revealed that he possessed audio tapes in which Wilbur tells Mason about some of the other personalities she has already seen in prior sessions.

Spiegel made these claims 24 years later, after Schreiber, Wilbur and Mason had all died and he was finally asked about the topic.

[12] In August 1998, psychologist Robert Rieber of John Jay College of Criminal Justice stated that the tapes belonged to him and that Wilbur had given them to him decades earlier.

[15] Debbie Nathan's Sybil Exposed[8][16][17] draws upon an archive of Schreiber's papers stored at John Jay College of Criminal Justice[18] and other first-hand sources.

In addition, Suraci claims that Spiegel behaved unethically in withholding tapes which supposedly proved Wilbur had induced Mason to believe she had multiple personalities.