What gives a face its ethnicity?

We can quickly and easily judge faces in terms of their ethnicity. What is the basis for our decision? Other studies have used either eye tracking (e.g., Armann Bülthoff 2009) or the Bubbles method (e.g., Gosselin Schyns 2001) in categorization tasks to investigate which facial features are used for sex or identity classification. The first method investigates which parts are preferentially looked at while the latter method shows which facial regions, when shown in isolation during the task, leads to correct classification. Here we measured the influence of facial features on ethnicity classification when they are embedded in the face of the other ethnicity. Asian and Caucasian faces of our 3D face database (http://faces.kyb.tuebingen.mpg.de) had been paired according to sex, age and appearance. We used 18 pairs of those Asian-Caucasian faces to create a variety of mixed-race faces. Mixed-race faces were obtained by exchanging one of the following facial features between both faces of a pair: mouth, nose, facial contour, shape, texture (skin) and eyes. We showed original and modified faces one by one in a simple ethnicity classification task. All faces were turned 20 degrees to the side for a more informative view of nose shape, face shape and facial contour while eyes and mouth and general face textures were still fully visible. Because of skin color differences between exchanged parts and original faces, all 3D faces were rendered as grey-level images. The results of 24 Caucasian participants show that the eyes and the texture of a face are major determinants for ethnicity classification, more than face shape and face contour, while mouth and nose had weak influence. Response times showed that participants were faster at classifying less ambiguous faces