The human brain is an extremely complex instrument. Over a lifetime, people learn a great deal about just about everything. Some of these things can be enumerated into rules and opinions—others cannot, but just manifest themselves as “gut feelings”. This phenomenon has been well documented, especially in the case of police and fireman who (correctly) know something is wrong even if the facts aren’t yet apparent. In many cases, what your gut tells you turns out to be right—the problem is you often can’t say why. Of course, in this study, they appear to have helped things along by telling the subjects what characteristic they were trying to discriminate.
I agree that humans can spot stuff like this almost instantly. But, predictive qualities differ depending on many factors. For example, in my long experience as a straight male, I can spot a homosexual male much more quickly than a straight female can. That’s a little counter intuitive, but I think it’s true across the board. I wonder if females can detect lesbians as adroitly.
Maybe it’s because straight men don’t confuse effeminate behavior with sensitivity.
And no, I don’t always confirm my gut feelings. I don’t need to. They have been proven to be accurate enough when applied to the folks who subsequently acknowledge their preference.