Marissa Nederhouser, Michael C. Mangini, and Irving Biederman

Face matching suffers tremendously when the faces differ in contrast
polarity but no such costs are apparent when matching objects. Unlike face
matching, object matching can generally be accomplished by using discontinuities
that would be unaffected by changes in contrast polarity. Would object
recognition remain invariant when differences in edges and nonaccidental
properties were not available? Subjects matched pairs of smooth, blobby,
asymmetric volumes generated from the harmonics of a sphere. Changes in
contrast polarity had no effect on the matching of these stimuli, either for naïve
subjects or for “experts” that had practiced for over 8,000 trials with images of
positive contrast. These results suggest that faces are special with respect to
sensitivity to direction of contrast.