Faces play a very important role in our social life. We make complex social decisions based on facial appearance. Extensive research has been made to identify a set of facial features which make a face attractive. Possibly no research is needed to predict which face a heterosexual male would prefer when asked to choose between Megan Fox (voted as one of the sexiest celebrities) and Jocelyn Wildenstein (voted as one of the ugliest celebrities).

But we know little how we make a preference decision when the two faces are closely matched (e.g., age, race, gender, gaze, facial attributes, facial emotion). Is there any specific brain activity pattern associated with our preference (or non-preference)? Can these patterns be identified before our conscious decision?

These problems were addressed by a neuroimaging study led by Joydeep Bhattacharya at Goldsmiths, University of London, where human volunteers were asked to make a preference decision between two faces which are closely matched. Faces were presented one after the other and volunteers were instructed to choose the face that they would most like to approach and to talk to. Their brain waves (electroencephalogram) were continuously recorded.

"We found specific brain activity patterns which correlate to the decision making process," said Bhattacharya, "one pattern is specific to the face currently being looked at, and the other is specific to the face previously shown which is only available through mental recall, and surprisingly, both patterns occur well before the moment of conscious decision on which face is preferred. We also found some activity patterns which are possibly related to positive first impression effect."

Does this mean that brain decides first and tells us later?

Bhattacharya remarked, "This is a tricky question which troubles both neuroscientists and philosophers alike. We cannot prove from the current study that this is indeed the case, but there is ample evidence that we are not fully aware of the constituent brain processes leading to a conscious decision. The real challenge is to predict the final conscious decision based on these pre-conscious neural activity patterns on trial by trial basis and in real-time."

Other researchers involved with the study, published in the journal NeuroImage, are Job Lindsen and Rhiannon Jones from Goldsmiths, University of London and Shinsuke Shimojo from California Institute of Technology, USA.