Abstract
Studies of human social perception become more persuasive when the behavior of raters can be separated from the variability of the stimuli they are rating. We prototype such a rigorous analysis for a set of five social ratings of faces varying by body fat percentage (BFP). 274 raters of both sexes in three age groups (adolescent, young adult, senior) rated five morphs of the same averaged facial image warped to the positions of 72 landmarks and semilandmarks predicted by linear regression on BFP at five different levels (the average, ±2 SD, ±5 SD). Each subject rated all five morphs for maturity, dominance, masculinity, attractiveness, and health. The patterns of dependence of ratings on the BFP calibration differ for the different ratings, but not substantially across the six groups of raters. This has implications for theories of social perception, specifically, the relevance of individual rater scale anchoring. The method is also highly relevant for other studies on how biological facial variation affects ratings.
Highlights
This paper proposes an approach for calibrating facial stimuli that allows facial image input to be formalized by constraining variation solely to the biological or appearance variable of interest
Social perception studies of facial adiposity may serve as illustration: (1) Sometimes stimuli are not quantified at all when the correlation coefficient between BMI or body fat percentage (BFP) values and facial ratings is the statistical measure[4,5]
The present contribution fills this gap in the design of rating studies by controlling for characteristics of the stimulus and the rater at the same time. (Readers familiar with test theory may recognize this strategy as analogous to a combined Rasch scaling of ability and item difficulty in some approaches to school testing.10) To achieve the necessary control we produce images that vary solely in the facial shape consequences of the variable of interest, in our case BFP, rather than the innumerable other individual differences that usually blur the stimulus variable
Summary
This paper proposes an approach for calibrating facial stimuli that allows facial image input to be formalized by constraining variation solely to the biological or appearance variable of interest. The topic of BFP’s facial correlates is a suitable choice for demonstrating the method because facial correlates of BMI were the most integrated pattern[11] and at the same time contribute to current research into the social consequences of obesity or its opposite, which we refer to here as “leanness.” We modified the image unwarping and averaging previously explained in Windhager et al.[12] to yield a series of five facial configurations of female adolescents calibrated by BFP These were presented in a rating experiment in order to determine whether the larger, rounded mid- and lower face with increased BFP elicits associations with (i) babies’ chubby cheeks[13,14], or rather with (ii) masculinity and dominance due to the relative jaw prominence[15]. We did not predict systematic differences between male and female raters or among different age groups (adolescents, young and older adults)
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