(CNN) -- A Northwestern University psychology professor was in hot water Thursday for an after-class session in which a couple demonstrated the use of a sex toy.

University President Morton Schapiro said he was "troubled and disappointed" by the February 21 incident and had ordered an investigation.

"Many members of the Northwestern community are disturbed by what took place on our campus," Schapiro said in a statement. "So am I."

Professor J. Michael Bailey provided his own account of the optional event in his human sexuality course, saying he wants students to learn about sexual diversity and information from "real people."

Students who witnessed the incident had been told repeatedly by a guest speaker what was about to happen would be graphic, the professor said in a statement. About 100 students chose to attend following a larger lecture, affiliate WGN said.

Bailey invited speaker Ken Melvoin-Berg, co-owner of Weird Chicago Tours, who brought a woman and a man for a discussion on the female orgasm. Melvoin-Berg suggested they demonstrate use of high-powered equipment they brought, said the professor, who agreed to the idea.

"We gave them plenty of warning. We had nobody leave at that point," Melvoin-Berg told CNN Chicago affiliate WLS, adding the demonstration was meant to be educational. "We only got positive feedback, 100% positive feedback during and after. The students were respectful. They were smart and asked good questions, intelligent questions and seemed engaged in the idea of human sexuality," said Melvoin-Berg.

But apparently some students at the private school near Chicago left before or during the demonstration of what the professor described in a statement as "kinky" sex.

"For me, I'm glad I didn't see it. It was a little too explicit for me, and if I were in the class, if I would have stayed for the demonstration, I probably would have left. I know a couple of my friends did get up and leave," student Diana Lorenzini told CNN affiliate WLS.

Brianne Williams, another student, said "Dr. Michael Bailey is one of our finest professors here, and his class is about opening people's minds up."

Schapiro said he wants to determine what is appropriate for the classroom.

"Although the incident took place in an after-class session that students were not required to attend and students were advised in advance, several times, of the explicit nature of the activity, I feel it represented extremely poor judgment on the part of our faculty member," Schapiro said in his statement. "I simply do not believe this was appropriate, necessary or in keeping with Northwestern University's academic mission."

In his statement, Bailey said it was too early to tell whether he had regrets.

"I certainly have no regrets concerning Northwestern students, who have demonstrated that they are open-minded grown-ups rather than fragile children," the professor added.