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

Abstract

Face recognition is known to be impaired when the contrast polarity of the eyes is inverted. We studied how contrast affects early perceptual face processing by measuring the face-sensitive N170 component to face images when the contrast of the eyes and of the rest of the face was independently manipulated. Fixation was either located on the eye region or on the lower part of a face. Contrast-reversal of the eyes triggered delayed and enhanced N170 components independently of the contrast of other face parts, and regardless of gaze location. Similar N170 modulations were observed when the rest of a face was contrast-inverted, but only when gaze was directed away from the eyes. Results demonstrate that the contrast of the eyes and of other face parts can both affect face perception, but that the contrast polarity of the eye region has a privileged role during early stages of face processing.

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

“…Separate ERP wavefoms are shown for the four different face contrast types (contrast-normal, contrastinverted, positive-eyes chimera, negative-eyes chimera). For the Control group, the pattern of N170 modulations was similar to the effects previously observed with a different and younger 15 group of participants without face recognition impairments (Fisher et al, 2015). Inverting the contrast of the eye region resulted in enhanced and delayed N170 components in both fixation conditions, irrespective of the contrast of the rest of the face.…”

“…In the upper fixation condition (Figure 2) As can be seen in Figure 3, the N170 amplitude enhancement produced by inverting the contrast of the rest of the face was larger when the eye region was contrast-positive (as was already observed in our previous study; Fisher et al, 2015), and this modulation was more pronounced over the right hemisphere. Importantly, neither of these differential effects interacted with group, both F<1.…”

“…The procedures used in the present experiment were identical to those used in a previous study from our lab where participants without face recognition impairments were tested (Fisher et al, 2015). Contrast-normal faces, fully contrast-inverted faces, positive-eyes chimeras, and negative-eyes chimeras appeared in a random order in each block.…”

“…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.…”

“…In our earlier study with participants without face recognition impairments (Fisher et al, 2015), contrast-reversal of the eye region elicited enhanced and delayed N170 components, irrespective of the rest of the face, and independently of gaze location. Contrast-reversal of the rest of the face had no effect on the N170 when fixation was close to the eye region, but produced a delay and enhancement of the N170 when participants fixated between the nose and mouth.…”