A new study published in Journal of Sex Research has concluded that a "lack of erotic thoughts during sexual activity was the only significant predictor of men’s sexual desire." Meaning that dirty, sexy thoughts during sex will increase men's sexual satisfaction.
This study was done on 205 men ranging in age from 18-72 (average of 35) in Portugal. There are many cultural differences between residents of North American and Europe so, as the source writer points out, these results may not be applicable to North American men.
Even with that, it can't hurt to get yourself mentally turned on. I know that I love dirty talk just as well as dirty thoughts. I'm doing it right now.