That’s why the brain scans were so revealing.
You show images of masculine women, masculine men, feminine women, feminine men, different states of undress and lewdness and see what the brain does.
The human brain is quick to recognize lewdness, and the part of the brain that registers excitement does so according to interest. But another part acts like a filter, turning on to turn you off. Its why a straight guy who’s into musclegirls isn’t into buff guys, because one part of the brain says all of the above and another part says no to boys. Weaker reactions from the filter corresponded to people who said they thought the person was attractive or sexy but would not want to have sex with for real, and stronger filter reactions equaled actual disgust.
But people who identified as bisexual were all over the place. Strong reactions from the filter had them say they’d hit that, weak reactions and they’d grimace and say they don’t find it appealing. It was almost random, or like they had a second filter and were entirely disregarding the first.
Its also why some straight folks can fap to traps, or gay folks to straight porn. They have weaker filter reactions despite still having a physical IRL orientation. But they are not bisexual.
The study found women had less filter reactions on average, but when they did they were stronger despite saying they’d be with more people in real life. Men had particular tastes in fetish and fewer strong reactions to images, but were more choosy in real life partners. Some have suggested its because sexual fantasies for men are often based more heavily on visuals than those of women.