The Lightness Distortion Effect: Additive Conjoint Measurement Shows Race Has a Larger Influence on Perceived Lightness of Upright than Inverted Faces

[摘要] BACKGROUND African American faces are judged to be darker than Caucasian faces, even when faces are matched for mean luminance and contrast (Levin & Banaji, 2006). This is the Lightness Distortion Effect (LDE), which is found even when faces are blurred, suggesting that low-level visual features drive LDE to at least some degree (Firestone & Scholl, 2015). Here, the LDE is measured using maximum likelihood conjoint measurement (MLCM). Upright and inverted faces were tested separately to control for low-level visual features. METHODS The joint influence of (1) overall mean luminance and (2) race was measured for perceived face lightness. Thirteen African American faces ranging in mean luminance and contrast and 13 Caucasian faces, matched to the African American faces in mean luminance and contrast, were tested (Levin & Banaji, 2006). All pairs of the 26 faces (either upright or inverted, in separate runs) were presented straddling fixation for 250 msec, followed immediately by a noise mask (with replications, 1,800 judgments in all for each observer). Conjoint measurement requires that participants only choose which member of a pair appears lighter; this ameliorates concern about demand characteristics (e.g. Firestone & Scholl, 2015). Perceptual lightness scales for all 26 face stimuli were derived from MLCM. RESULTS & CONCLUSIONS Each observer's results were analyzed separately. For 5 of the 6 observers, race had a significant effect on lightness judgments of upright faces (p < 0.001 for each observer) in the direction of a fixed decrement in perceived lightness for each African American face. Further, the magnitude of this effect was greater for upright than inverted faces for 5 of the 6 observers (p < 0.05). The greater effect of race with upright than inverted faces shows that perception of face lightness depends on race beyond just low-level features.

[学科分类] 眼科学