Psychology lecturer Dr Gerulf Rieger helps Dr Christian Jessen test his sexual preferences on Channel Four show Undercover Doctor: Cure Me, I'm Gay tonight.

The one off documentary will see Dr Jessen explore the motives and practices behind therapies that offer to change people’s sexuality. He asks if it is possible to ‘cure’ homosexuality and will undertake some of these ‘cures’ to see if he can change his sexual preference.

Dr Rieger was asked to test Dr Jessen before he undertook any of the ‘cures’ and looked at his level of arousal when watching videos of different sexes.

Dr Rieger, who was working at Cornell University at the time before his move to Essex, said: “It was interesting to be part of the project and it is good to have the opportunity to disseminate our research. The production team were very well informed and very knowledgeable and particularly interested in investigating the political beliefs surrounding this issue.

“My view is that male sexuality is so fixed that you cannot do much to change a man's sexual orientation.”

Dr Rieger is an expert on sexual attraction and orientation. He is creating a lab at the University of Essex’s Colchester Campus to investigate sexual arousal and attraction and find a new, less invasive way of monitoring it through pupil dilation. He is also planning new research on the development of sexual orientation.