Lighting direction affects recognition of untextured faces in photographic positive and negative

Face recognition in photographic positive and negative was examined in a same/different matching task in five lighting direction conditions using untextured 3-D laser-scanned faces. The lighting directions were +60, +30, 0, -30 and -60 degrees, where negative values represent bottom lighting and positive values represent top lighting. Recognition performance was better for faces in positive than in negative when lighting directions were at +60 degrees. In one experiment, the same effect was also found at +30 degrees. However, faces in negative were recognized better than positive when the direction was -60 degrees. There was no difference in recognition performance when the lighting direction was 0 and -30 degrees. These results confirm that the effect of lighting direction can be a determinant of the photographic negative effect. Positive faces, which normally appear to be top-lit, may be difficult to recognize in negative partly because of the accompanying change in apparent lighting direction to bottom-lit.