To test this hypothesis, the researchers used functional Magnetic Resonance Imaging (fMRI), a non-invasive technique that permits the localization of regions in the human brain activated during cognition and experience. The researchers scanned 40 subjects (10 heterosexual women, 10 heterosexual men, 10 homosexual women, 10 homosexual men, mean age 26 ± 3 years) that were classified as hetero- or homosexuals on the basis of their self-report. While in the MR scanner, the subjects either passively viewed faces or pressed one of three buttons to indicate whether a face was Attractive, Neutral, or Unattractive, and reaction times were recorded.
Behaviorally, regardless of their gender and sexual orientation, all subjects rated the attractiveness of both male and female faces very similarly, suggesting that men and women equally notice and respond to beauty of individuals of the same and opposite sexes. Interestingly, all subjects, regardless of their gender or sexual preference, also showed virtually identical patterns of neural activation in regions in the visual cortex and the limbic system, where male and female faces elicited responses of similar magnitude. The findings indicated that invariant (facial identity) and variant (facial expression) features are similarly processed in the brain, independent of the gender of the individual who is viewed or the sexual orientation of the viewer.
The researchers found that, consistent with their hypothesis, the gender of a viewed individual, when the sexual preference of the viewer was taken into account, did make a difference in the reactions seen in the