The functional basis of face evaluation

Abstract

People automatically evaluate faces on multiple trait dimensions, and these evaluations predict important social outcomes, ranging from electoral success to sentencing decisions. Based on behavioral studies and computer modeling, we develop a 2D model of face evaluation. First, using a principal components analysis of trait judgments of emotionally neutral faces, we identify two orthogonal dimensions, valence and dominance, that are sufficient to describe face evaluation and show that these dimensions can be approximated by judgments of trustworthiness and dominance. Second, using a data-driven statistical model for face representation, we build and validate models for representing face trustworthiness and face dominance. Third, using these models, we show that, whereas valence evaluation is more sensitive to features resembling expressions signaling whether the person should be avoided or approached, dominance evaluation is more sensitive to features signaling physical strength/weakness. Fourth, we show that important social judgments, such as threat, can be reproduced as a function of the two orthogonal dimensions of valence and dominance. The findings suggest that face evaluation involves an overgeneralization of adaptive mechanisms for inferring harmful intentions and the ability to cause harm and can account for rapid, yet not necessarily accurate, judgments from faces.

Fig. 1.

A 2D model of face evaluation. (A) Examples of a face varying on the two orthogonal dimensions, trustworthiness and dominance. The face changes were implemented in a computer model based on trustworthiness (study 3) and dominance judgments (study 4) of 300 emotionally neutral faces. The extent of face exaggeration is presented in SD units. (B) Mean trustworthiness judgments of faces (study 5) generated by the trustworthiness model. (C) Mean dominance judgments of faces (study 6) generated by the dominance model. The judgments were made on 9-point scales. Error bars show standard error of the mean.

Fig. 2.

Sensitivity of trustworthiness and dominance dimensions to cues resembling emotional expressions. (A) Intensity color plot showing face categorization as neutral or as expressing one of the basic emotions as a function of their trustworthiness and dominance (study 7). (B) Mean judgments of expressions of anger and happiness (study 8). The judgments were made on a 9-point scale, ranging from 1 (angry) to 5 (neutral) to 9 (happy). Error bars show standard error of the mean. The line represents the best linear fit. The x-axis represents the face exaggeration in SD units.

Fig. 3.

Sensitivity of trustworthiness and dominance dimensions to cues related to physical strength. (A) Mean judgments of facial maturity (study 9) as a function of the trustworthiness and dominance of faces. The direction of the trustworthiness dimension was reversed to show that the slopes for the change from trustworthy to untrustworthy faces and the change from submissive to dominant faces were identical. (B) Mean judgments of facial maturity (study 10) of faces with masked internal features. The judgments were made on a 9-point scale, ranging from 1 (baby-faced) to 5 (neutral) to 9 (mature-faced). (C) Mean judgments of femininity/masculinity (study 11). (D) Mean judgments of femininity/masculinity (study 12) of faces with masked internal features. The judgments were made on a 9-point scale, ranging from 1 (feminine) to 5 (neutral) to 9 (masculine). The x-axis in the figures represents the extent of face exaggeration in SD units. Error bars show standard error of the mean. The lines represent the best linear fit.