Abstract
Behavioural studies consistently demonstrate a female advantage for face processing. Evoked potentials have also shown gender effects with men displaying more right-lateralized activation for faces while women appear functionally bilateral (Proverbio, 2006). Together, these results suggest gender differences in face processing at a cortical level. Similar hemispheric asymmetry in men is documented for cognitive tasks such as mental rotation. However, handedness mediates this trend. Imaging research demonstrates increased left-hemisphere activation for mental rotation in left-handed (LH) men, indicating less hemispheric asymmetry than right handed (RH) men (Shimoda, 2007). Structural differences attributable to handedness are also evident in the corpus callosum. Research has shown that RH homosexual men display structural differences in the corpus callosum similar to those of LH heterosexual men (Witelson, 2007). Furthermore, homosexuality is positively correlated with non-right-handedness in both men and women (Lalumière, 2000). RH homosexual men show female-typical performance patterns on many sexually dimorphic cognitive tasks (Rahman, 2003). This suggests less functional asymmetry in homosexual men regardless of handedness. Findings regarding handedness and sexual orientation in women, however, are less consistent. We explored the implications of these trends for face processing by comparing performances of LH and RH heterosexuals to RH homosexual men and women on a battery of face perception tasks (old-new recognition, configural, featural and composite face processing). Results demonstrate a dissociation in performance for heterosexual men and women as a function of handedness— RH women were better than RH men whereas LH men outperform LH women. Moreover, homosexual men outperform RH heterosexual men and were therefore comparable to heterosexual LH men and RH women. These results show that sex, handedness and sexual orientation play a role in face perception ability. Further, LH men and homosexual men's similar performance may reflect underlying structural similarities involved in face processing.
JKES is supported by NSERC and CFI.