Contrast negation and the importance of the eye region for holistic representations of facial identity.

Reversing the luminance values of a face (contrast negation) is known to disrupt recognition. However, the effects of contrast negation are attenuated in chimeric images, in which the eye region is returned to positive contrast (S. Gilad, M. Meng, & P. Sinha, 2009, Role of ordinal contrast relationships in face encoding, Proceedings of the National Academy of Sciences, USA, Vol. 106, pp. 5353-5358). Here, we probe further the importance of the eye region for the representation of facial identity. In the first experiment, we asked to what extent the chimeric benefit is specific to the eye region. Our results showed a benefit for including a positive eye region in a contrast negated face, whereas chimeric faces in which only the forehead, nose, or mouth regions were returned to positive contrast did not significantly improve recognition. In Experiment 2, we confirmed that the presence of positive contrast eyes alone does not account for the improved recognition of chimeric face images. Rather, it is the integration of information from the positive contrast eye region and the surrounding negative contrast face that is essential for the chimeric benefit. In Experiment 3, we demonstrated that the chimeric benefit is dependent on a holistic representation of the face. Finally, in Experiment 4, we showed that the positive contrast eye region needs to match the identity of the contrast negated part of the image for the chimera benefit to occur. Together, these results show the importance of the eye region for holistic representations of facial identity.