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

Abstract

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.

Effects of contrast inversion on face perception depend on gaze location: Evidence from the N170 component

“…Recent studies have shown that restoring the normal contrast polarity of the eye region while the rest of the face remains contrast-inverted improves recognition performance (Gilad et al, 2009;Sormaz et al, 2013) and can eliminate inversion-related N170 modulations (Gandhi et al, 2012). The present experiment demonstrates that contrast-inversion of the eyes or of the rest of the face can both affect N170 components, depending on which part of a face is fixated.…”

“…Inverting the contrast of the eyes should therefore have a greater effect on face processing than contrast inversions of other parts of a face, in particular when eye gaze is directed towards its preferred position near the eye region. Gilad, Meng, and Sinha (2009) explored this hypothesis with "contrast chimera" faces, which include both contrast-inverted and contrast-normal regions, and demonstrated that restoring only the eye region of a contrast-inverted face to positive contrast improved recognition performance to approximately 90% of the level observed with contrast-normal faces (see also Sormaz, Andrews, & Young, 2013). They also showed that fMRI activity in the fusiform face area elicited by these positive-eyes chimeras was indistinguishable from the response to contrast-normal faces.…”

Reduced sensitivity to contrast signals from the eye region in developmental prosopagnosia

“…Because the eye region contains several important contrast-related signals (e.g. the boundaries between the sclera, iris and pupil of the eye, and contrast differences between the eyes and surrounding regions including eyebrows), inverting the contrast polarity of this region is particularly detrimental for face recognition, and restoring this region to normal contrast eyes in an otherwise contrast-inverted face leads to dramatic improvements in recognition performance (Gilad et al, 2009;Gandhi et al, 2012;Sormaz et al, 2013).…”

“…These images were generated by selectively inverting the contrast of the eye region within an otherwise normal-contrast face (negative-eyes chimeras) or by leaving the eye region unchanged and contrast-inverting the rest of the face (positive-eyes chimeras; see Figure 1A). Previous studies have shown that restoring 7 the normal contrast of the eye region in an otherwise contrast-inverted face improved face recognition to approximately 90% of the level observed for normal-contrast faces (Gilad et al, 2009;Sormaz, Andrews, & Young, 2013), and also strongly reduced the effects of contrast inversion on the N170 component (Fisher, Towler, & Eimer, 2015;Gandhi, Suresh, & Sinha, 2012). Such observations demonstrate that contrast signals from the eye region are particularly important during early perceptual stages of face processing.…”

“…Such observations demonstrate that contrast signals from the eye region are particularly important during early perceptual stages of face processing. These stages appear to be specifically sensitive to deviations from the typical contrast within this region, presumably because contrast-related signals from this region are particularly important for face detection and face recognition processes (e.g., Gilad et al, 2009;Peterson & Eckstein, 2012;Sormaz et al, 2013). Participants with intact face processing abilities tend to fixate the area between both eyes during face perception and recognition tasks (Hsiao & Cottrell, 2008).…”