OSHKOSH, Wis. — The case of a man charged with raping a woman with multiple personalities is raising new questions about sexual consent and mental illness.

The victim claims several of her personalities were raped, but 29-year-old Mark A. Peterson contends one of the woman’s personalities consented.

“If (the woman) is not palpably mentally ill, then the prosecution has problems,” said Leonard Kaplan, a University of Wisconsin Law School professor observing the case in Oshkosh, a city of 50,000 in east-central Wisconsin. “If she is mentally ill, she can’t consent.”

Winnebago County Circuit Judge Robert Hawley was expected to determine Thursday whether enough evidence exists to order Peterson to stand trial on a charge of second-degree sexual assault. The charge carries a maximum of 10 years in prison and $10,000 in fines.

The victim, a 26-year-old woman, has as many as 18 different personalities, a mental illness that typically develops after a traumatic childhood experience, psychologists said.

She told police two of her personalities — Jennifer, 20, a fun and promiscuous lady, and Emily, a vulnerable 6-year-old girl — were assaulted by Peterson in June.

The defense counters the woman consented and Peterson had no idea if the woman was mentally ill.

District Attorney Joseph Paulus said he will be forced to introduce several of the victim’s personalities to a jury through her testimony during the trial, expected in October.

“I wouldn’t say I’m looking forward to it. … It is unusual,” Paulus said. “You are talking about a subject matter that is somewhat foreign to everybody.”

Defense lawyer Edward Salzsieder has asked that the charge be dismissed.

“There is a question of when does anybody know a person is mentally ill,” he said.

According to court records, the woman met Peterson June 9 at a park when the victim was portraying a personality she called Franny.

Two days later, Peterson went to the woman’s home and invited her out for coffee. At the restaurant, the woman reportedly introduced some of her personalities to Peterson, including Jennifer, the records said.

After the pair left the restaurant, Jennifer agreed to have sexual intercourse at the man’s suggestion in a car, Peterson told police.

The criminal complaint alleged Peterson noted that during sex, the woman’s 6-year-old personality, Emily, appeared before the woman eventually became Franny again.

Neighbors have told police they warned Peterson that the woman had a mental disorder.

Paulus said he must prove three things — that the victim had a mental illness, that she was incapable of appraising her own conduct and that Peterson knew about the illness.

Kaplan said, “It could turn out to be the battle of the experts and persuading a jury which expert is right.”

Multiple-personality disorder is usually caused by early childhood trauma — especially sexual abuse — and affects one person in 10,000, said Dr. Nancy Perry, a Milwaukee clinical psychologist.

The patient separates one part of his or herself from another to avoid facing the trauma, Perry said.