Background Moral judgments are influenced by facial attractiveness. Moral behavior of good-looking people is more judged as morally beautiful and specifically activates brain regions involved in the representation of emotional meaning. In moral judgments, immoral behavior is more diagnostic than moral behavior. However, it is not clear whether the implied relationship between face and moral traits affects people's judgments of immoral behavior. The present study is the first to investigate the neural responses to facial attractiveness in the judgments of moral badness and ugliness. Results Experimental materials consisted of scenarios depicting behaviors at different levels of immorality acted by good- or ugly-looking males in daily life. Subjects were asked to rate how bad and how ugly the male immoral behavior was on a 4-point scale. A parametric general linear model (GLM) was performed to estimate neural response to face attractiveness that varies with the levels of immorality in the judgments of moral badness and moral ugliness. Results showed that ugly faces both in the judgments of moral badness and moral ugliness activated the anterior cingulate/medial prefrontal cortex and bilateral inferior occipital gyrus, suggesting that ugly faces in evaluation of immoral behavior elicited activity in brain regions associated with underlying general emotions and automatically processed visual features of faces. In addition, compared with ugly faces in moral badness judgment, ugly faces in moral ugliness judgment showed stronger activity in the ventromedial prefrontal cortex, left insula, left middle temporal gyrus and cortical midline structures, and specifically activated bilateral frontal poles. These brain regions are mainly involved in the representation of emotional meaning of faces, suggesting that emotional information carried by ugly faces only affects moral aesthetic judgment. And no differential activation was found for the opposite contrast. Conclusion The results of this study demonstrate that facial attractiveness is task-specific as well as task-general in evaluating the badness and ugliness of immoral behavior. The findings provide more experimental and neurological evidence for the impact of implied relationships between faces and moral traits on higher moral decision-making. Our findings are of great significance to the understanding of the essence between morality and aesthetics.

Objective: Unethical behavior has a powerful effect on an individual's overall judgment and is easily influenced by their looks. However, it remains unclear whether the unethical behavior of ugly-looking individuals is more likely to be judged as immoral and what the mechanisms behind it are. The present study investigates whether facial ugliness influences the bad and ugly judgments of unethical behavior from the perspective of neural mechanisms. Method: The experimental material consisted of scenarios describing different levels of unethical behavior committed by ugly-looking or non-ugly-looking people. Subjects were asked to rate the bad and ugly levels of behaviors on a 4-point scale while being scanned for brain activity. We conducted a parametric general linear model (GLM) to estimate neural responses to facial ugliness in morally bad and ugly judgments, which varied with the level of immorality. Results: The results showed that ugly-looking faces activated the anterior cingulate cortex and bilateral inferior occipital gyrus in both judgments, indicating a task-general pattern. Ugly-looking faces in morally ugly judgment showed stronger activity than in morally bad judgment in the ventromedial prefrontal cortex, left insula, left middle temporal gyrus, and cortical midline structures that characterize the emotional significance of events, suggesting a task-specific pattern. Conclusions: The results of the current study demonstrate that facial ugliness is task-specific as well as task-general in evaluating unethical behaviors. The findings provide more experimental and neurological evidence for the understanding of the essence between morality and aesthetics.