This was in contrast to lesbians, who showed much stronger sexual responses to women than to men.
The researchers said lesbians were the most like men in their responses because it is usually men who show distinct sexual responses to their favourite sex.
Dr Rieger said: "Even though the majority of women identify as straight, our research clearly demonstrates that when it comes to what turns them on, they are either bisexual or gay, but never straight."
Dr Rieger also said his study showed that lesbians who may dress in a more masculine way may not have more masculine behaviours.
"Although some lesbians were more masculine in their sexual arousal, and others were more masculine in their behaviours, there was no indication that these were the same women," he said.
"This shows us that how women appear in public does not mean that we know anything about their sexual role preferences."