The judgments of moral goodness and moral beauty objectively refer to the evaluation of moral behaviors or moral traits (i.e., kindness, virtue, etc.), which is generally influenced by facial attractiveness. But it is not clear whether facial attractiveness has similar or different influence on the judgments of moral goodness and moral beauty. In the current study, we investigated the neural responses to facial attractiveness under two conditions of higher order moral decision-makings: moral goodness judgment and moral beauty judgment. The same subjects were required to evaluate the level of goodness about the positive moral behavior and the level of inner beauty of the person doing that same behavior with different levels of facial attractiveness (beautiful or ugly face). During the whole experiment, subjects were not instructed to pay attention to an individual`s face, but were asked to make moral judgments based on this individual`s moral behavior. So, what we're talking about is whether the subjects' judgments on the moral behavior of an individual is affected by the individual`s facial attractiveness, with the focus on the influence of implicit perception of facial attractiveness on higher social decisions, which is more in line with natural situations and reality in terms of decision making and has certain ecological validity.
We have four main findings. First, behavioral results indicated that the morally positive behaviors performed by individuals with beautiful faces were more likely to be evaluated as morally good and morally beautiful than behaviors performed by individuals with ugly faces, as indexed by the rating scores but not response time. Second, neuroimaging results showed that, similar to beautiful faces in moral goodness judgment trials, beautiful faces in moral beauty judgment trials recruited an overlapping of the left ventral occipitotemporal extrastriate cortices (OTC) sensitive to the early perceptual processing of faces, including inferior occipital gyrus (IOG) and fusiform face area (FFA). Third, compared to beautiful faces during moral goodness judgment, beautiful faces during moral beauty judgment induced specific activity in the ventral medial prefrontal cortex (vmPFC) (i.e., ACC extending to mOFC) and left PCC/precuneus. The opposite comparison elicited specific activity in the left premotor area extending to the opercular part of the inferior frontal gyrus (IFG). Moreover, compared to ugly faces during moral goodness judgment, ugly faces during moral beauty judgment induced specific activity in the left temporo-parietal junction (TPJ). The opposite comparison elicited no significant cluster. Fourth, the right lateral orbitofrontal cortex (OFC) was commonly involved in the representations of moral goodness and moral beauty, but was not regulated by facial attractiveness. Our results demonstrated that the neural responses to facial attractiveness in the process of higher moral decision-makings exhibits both task-general and task-specific characteristics. Facial attractiveness contributes similarly and differently to the judgments of moral goodness and moral beauty.
Shared response to attractive faces in the judgments of moral goodness and moral beauty
In the current study, we hypothesized that the judgments of moral goodness and moral beauty would be associated with enhanced activations in regions involved in the early perceptual processing of attractive faces, given that visual features pertaining to facial attractiveness would be apprehended automatically (Hung et al., 2016; Palermo & Rhodes, 2007) at a glance (Olson & Marshuetz, 2005) and influence people’s social judgments made about others (Chatterjee, 2003, 2015; Chatterjee et al., 2009; Chatterjee & Vartanian, 2016; Moonja Park Kim & Rosenberg, 1980; Todorov et al., 2008; Winston et al., 2007). Consistent with our expectation, we found that the left ventral occipitotemporal visual cortices, including IOG and FFA, responded to the beautiful faces independent of judgment task, showing a similar magnitude of activation during both judgments of moral goodness and moral beauty.
Previous studies confirmed that the apprehension of attractive faces is associated with an identifiable neural response, specifically, attractive faces automatically activate the ventral occipitotemporal cortices, particularly sensitive to face perception, including IOG and FFA (Chatterjee et al., 2009; Kranz & Ishai, 2006; Winston et al., 2007). An attractive face is a salient social signal that reflect the overall effect of all physical attributes of a face (Rhodes, 2006). Regions of the occipital and posterior temporal visual cortices involved in the lower-level visual processing of perceptual features of faces plays a critical role in the perceptual processing of attractive faces (Chatterjee et al., 2009). Recent fMRI studies also showed that the cognitive and neural mechanisms involved in the perceptual analyses of faces and attractive faces were considerably overlapping (Calder & Young, 2005; Fisher et al., 2016; Li et al., 2019; Redfern & Benton, 2017; Sun et al., 2015). The face-selective neurons in the occipitotemporal cortical visual areas is tuned to the identity of faces (Eick et al., 2020), and has representations that are invariant with respect to, for example, retinal position, size and even view. These invariant representations are ideally suited to provide the inputs to brain regions such as mOFC that is involved in social communication and emotional behaviors.
Combining our behavioral findings, that individuals with a beautiful face who perform moral behaviors are more likely to be judged as morally good and internally beautiful, compared with individuals with an ugly face who perform the same behaviors, our imaging result, that the neural activity involved in the perceptual apprehension of attractive faces was activated in both judgment tasks of moral goodness and moral beauty, demonstrates that both the judgments of moral goodness and moral beauty require the automatic visual analysis of the geometrical configuration of attractive faces of individuals performing moral behaviors, before attractive information can be transmitted to the extended emotional system involving in emotional representations. Our result is consistent with the previous findings that the occipital and posterior temporal visual cortices are responsive to the perceptual processing of attractive faces and remain present even when subjects are not attending explicitly to facial attractiveness (Chatterjee et al., 2009; Winston et al., 2007). We suggest that the perceptual processing of visual features of attractive faces is equally crucial for both forms of moral decision-making. It is in line with the view that the perceptual response to attractive faces involves a pattern of domain nonspecific regional activations (Chatterjee et al., 2009).
Different response to attractive faces in the judgments of moral goodness and moral beauty
In addition to the overlapping brain regions (IOG and FFA) activated by the beautiful faces, we also found that beautiful faces activated unique brain regions for each task, specifically, in moral goodness judgment, the left superior temporal cortex (STC), anterior temporal lobule (ATL) and premotor area extending to the opercular part of the inferior frontal gyrus (IFG) showed a significant increase in activation for beautiful faces compared to ugly faces; the left premotor area extending to the opercular part of the IFG was more activated by beautiful faces compared with the activity of beautiful faces in moral beauty judgment; whereas in moral beauty judgment, the midline cortical structures (MCS), including vmPFC/ACC/mOFC, PCC and precuneus, showed a significant increase in activation for beautiful faces. That beautiful faces in different judgment tasks activated different brain regions might imply that the representation of emotional aspects of attractive faces is task-specific, that is, different moral judgments might interpret emotional signals expressed by attractive faces in different ways.
Early perceptual processing of the attractive faces needs to be linked to many other brain structures which are mainly involved in emotional representations, to accomplish the evaluation of attractive faces. Because attractiveness has effects in later stages whereby identity and affective qualities are extracted from faces after the early structural encoding stage of face perception (Hahn & Perrett, 2014). Calder and Young (2005) proposed that the invariant and variable features (geometrical configuration) of faces may be encoded by the same perceptual characterization system, followed by separation (Li et al., 2019). Separate representations are constructed that make explicit information useful for recognizing facial identity or recognizing the affective qualities of faces at a step that is subsequent to perceptual processing. Recognizing actions (variant changes in facial expressions) and emotions from perceptual information in faces form the basis for understanding the intentions and feelings of others and allow us to successfully navigate our social world (McArthur & Baron, 1983; Thornhill & Gangestad, 1999).
Neural responses to attractive faces in moral goodness judgment task
The recognition of identity is based on the perception of aspects of facial structure that are invariant across changes in expression and other movements of the eyes and mouth, generally recruits the FFA, which is especially involved in representing the static features of faces, and the superior temporal sulcus (STS) especially involved in representing the dynamic, changeable features of faces (Bruce & Young, 1986; Hasselmo et al., 1989; Haxby et al., 2000, 2002; Hoffman & Haxby, 2000; Winston et al., 2004). STS and FFA neurons could be form detectors sensitive to particular configurations of the face surface, together, encoding a sequence of face configurations corresponding to a particular facial expression, act as a motion pattern detector (Giese & Poggio, 2003; Said et al., 2011). An additional face-selective region has been identified in the anterior temporal lobule (ATL) (Jonas et al., 2016), associated with dynamic aspects of face perception (Calder et al., 2007; Pitcher et al., 2011). In addition to the STC, an extended network for facial expression perception reaches the frontal operculum and premotor cortex. IFG and nearby motor areas show activity during the perception of facial expression and may have a causal role in their recognition (Pitcher et al., 2008; Pitcher, Dilks, et al., 2011). The STC serves as the visual input of the dynamics of the facial expression, and posterior IFG and adjacent ventral premotor cortex, which generates higher-level motor plans of expression action (Dijksterhuis & Bargh, 2001; Iacoboni & Dapretto, 2006; Monfardini et al., 2013; Yang et al., 2015). The recognition of facial identity is particularly well suited for the mirror neurons hypothesis, as it is known that humans mimic the facial expression of people they are interaction with and produce micro-expressions when simply looking at expressive face images (Dijksterhuis & Bargh, 2001; Dimberg, 1982; Dimberg et al., 2000; Monfardini et al., 2013). When perceiving and decoding other individuals` expression signals and inferring their underlying intentions, the observer may try to understand what the actions would mean if they themselves were to perform the same actions; the role of the observer`s self is much more prominent and the understanding of others` actions is relatively self-based (Iacoboni & Dapretto, 2006; Yang et al., 2015).
Our results showed that the brain networks of beautiful faces in moral goodness judgment task appeared to be consistent with the neural activity in the recognition of facial identity. The attractive face of the main character who performs a moral behavior captures the observer's attention (Chen et al., 2012; Leder et al., 2010), and the perceptual processing of attractive face might rely heavily on the observer`s self. The observation and understanding of the action here should refer to the visual features of attractive faces, rather than the moral action itself, because individuals with an ugly face also performs the same moral behavior, but there are no significant brain regions activated. We noticed that in moral goodness judgment task, information about the perceptual processing of beautiful faces was not transmitted to the brain regions responsible for processing the emotional aspects of attractive faces, for example, the vmPFC, and particularly the mOFC. This result is consistent with the affective-meaning-centered view of vmPFC, that is, vmPFC and its subcortical connections are not essential for simple forms of affects, valuation and affective learning, but are essential when conceptual information drives affective physiological and behavioral responses (Benoit et al., 2014; Roy et al., 2012). Indeed, the appreciation of attractive faces unfolds as a neurobiological process in which sensory information is projected to the reward circuit, which generates levels of pleasure (Skov & Nadal, 2020). Although the perceptual representation of a face is obviously important to how it is appreciated, its positive emotional impact is not inherent to this perceptual representation. Rather, emotional values must be understood as a gloss that applied onto sensation by the mesocorticolimbic system (Ellingsen et al., 2015). We speculate that in moral goodness judgment, the observers were likely to observe and imitate the specific facial features and expressions to mediate the influence of attractive faces on the moral goodness judgment, and did not concern themselves with the emotional meanings of attractive faces.
Neural responses to attractive faces in moral beauty judgment task
The recognition of emotional meanings is derived from facial features that resemble facial expressions signaling approach/avoidance behaviors (Todorov et al., 2008), and is generally modulated by a network of structures, including mOFC, cingulate cortex and ventral striatum (Maddock et al., 2003; Rolls, 2019; Vuilleumier et al., 2001). Most brain structures that participate in the recognition of emotions or the social significance of faces involve both perceptual processing - identifying the geometric configuration of facial features in order to discriminate among different stimuli on the basis of their appearance - and recognition of the emotional meaning of a stimulus - knowing that a certain expression signals an emotion (Adolphs, 2002). in moral beauty judgment, beautiful faces of the main characters who perform morally positive behaviors did not activate the superior temporal cortex (STC) and mirror nervous system, but significantly evoked the vmPFC (i.e., ACC extending to the mOFC) and left PCC/precuneus, which seemed to be consistent with the neural activity in the recognition of emotional aspects of attractive faces.
Work from fMRI studies have consistently shown that the vmPFC, particularly the mOFC, is relevant to the evaluation of attractive faces (Aharon et al., 2001; Bray & O’Doherty, 2007; Cloutier et al., 2008; Hampshire et al., 2012; Ishizu & Zeki, 2011; Kawabata & Zeki, 2004; Kawasaki et al., 2001; Liang et al., 2010; Marinkovic et al., 2000; O’Doherty et al., 2003; Smith et al., 2016; Tsukiura & Cabeza, 2011a, 2011b; Winston et al., 2007; Zaki et al., 2011). The vmPFC has been shown not only to underlie subjective experiences of emotional value, but also, more specifically, to underlie valuation that incorporates conceptual information to produce "affective meaning" (Aydogan et al., 2018; Roy et al., 2012; Winecoff et al., 2013). Neurons located in vmPFC, especially the mOFC, appear to integrate information from different sources (Knutson & Genevsky, 2018) and drive affective physiological and behavioral responses (Roy et al., 2012). The vmPFC also plays an important role in emotional regulation of behavior, particularly at the intersection of emotion and decision-making. Damaged to the vmPFC, results in both blunted emotional responses, demonstrated by reduced psychophysiological responses to emotional stimuli, and abnormal decision making (Rolls & Grabenhorst, 2008). The extensive connections between occipitotemporal visual regions and the prefrontal cortex (Seltzer & Pandya, 1989) provide for an effective source of perceptual input to the vmPFC and also make it plausible that the vmPFC could play a role in recognizing facial emotion via direct modulation of activity in occipitotemporal cortex via feedback (Adolphs, 2002). In addition, there is evidence that the recognition and experience of emotion are closely related, and in principle, consistent with the idea that the mOFC participates in emotion recognition via triggering an emotional response in the observer, and more importantly, this process depends on the context and the task (Emery & Amaral, 1999). That brain regions associated with reward information respond to attractive faces suggests physical attractiveness may hold incentive salience (Berridge & Robinson, 2003) and influence the observer`s perception of moral beauty.
Moreover, a number of fMRI studies have found that the midline cortical structures (MCS), including ACC, PCC and precuneus, are related to the self-referential processing, and self-referential thought, related to hopes and aspirations, tends to be associated with the anterior midline regions whereas self-referential thought related to duties and obligations is associated with the posterior midline regions (Johnson et al., 2006; Nejad et al., 2013). The result that the ACC, PCC and precuneus tended to respond more strongly to attractive faces than unattractive faces in moral beauty judgment suggests that MCS activations might be involved in the higher order processing of self and positive emotional-related information (Quevedo et al., 2018; Sugiura, 2015) and this processing is more likely to occur in moral beauty judgments than moral goodness judgment. Once again, this pattern of activations bears a strong resemblance to that associated with positive emotional expressions (Dolan et al., 1996; Kesler-West et al., 2001; Phillips et al., 1998). The highly consistent presence of these areas suggests that under certain tasks, attractive faces modulate activity in emotional meanings regions of the brain. This result is very important. For a long time, the academic has proposed that the generation of aesthetic feelings is influenced by the external image of the object, while the generation of moral sense is not affected (Zaidel & Nadal, 2011), but this is only from a speculative perspective. The results of the present study not only provide empirical evidence for this important principle, but uncover this critical difference only exist in the late encoding stage of object perception.
In addition, it is important to note that we found that the common neural representations of moral goodness and moral beauty was localized in the right lateral OFC, but its activity was not affected by facial attractiveness in either of judgment tasks. This result is consistent with some findings of the OFC`s role in social reward value, that lateral portions of the OFC are significantly more responsive to rewarding objects in general, while medial portions are involved in processing the emotional aspects of faces, including emotional valence and facial attractiveness (Aharon et al., 2001; Chatterjee et al., 2009; Cloutier et al., 2008; Ishai, 2007; Kawabata & Zeki, 2004; Liang et al., 2010; Pegors et al., 2015; Troiani et al., 2016). This result is also in line with the view that the brain requires a domain-general common currency signal, localize in the ventrolateral PFC, when comparing and deciding between different rewards (Delgado, 2007; Levy & Glimcher, 2012; Peters & Buchel, 2009; Sescousse et al., 2015), whereas adaptive behavior may require a domain-specific value signal generally located in the central OFC (Heinzelmann et al., 2020; Howard et al., 2015; Howard & Kahnt, 2017). In the present study, subjects were asked to compare and decide between different morally positive behaviors, and they were not directed to attend to the faces, which are value signals of adaptive behaviors, of individuals who perform moral behaviors. Although some studies have found that the lateral OFC also responds to beautiful faces (left latOFC: Winston et al., 2007; right latOFC: Tsukiura & Cabeza, 2011), this activity for face attractiveness may only arise when participants are explicitly evaluating face attractiveness (Pegors et al., 2015). Other studies have found that the role of the lateral OFC in aesthetic preference is not limited to the representation of the reward value of stimuli regarded as beautiful, it also seems to play a role in the processing of stimuli rated as not beautiful (Munar et al., 2012).
In brief, the present study directly compared the facial attractiveness under two conditions of higher order moral decision-makings: moral judgment and moral beauty judgment and examined the commonalities and differences in the neural responses to facial attractiveness during these two processes through an experimental approach. However, there are also several limitations in this study. First, we must admit that scene drawings used as experimental materials could lower the ecological validity of the study. Although the drawings give us a high level of control, in "real life," we look at human faces in action; even looking at a still photo drops ecological validity, but has more than a cartoon drawing. Second, we only recruited female subjects to participate in the experiment. Although we were doing it to eliminate the possible confusion between the gender of the subjects and the gender of the protagonist in the experimental stimulus, we must admit that this is also a limitation of the current study. Therefore, in future studies, we should recruit male subjects to complete different types of moral judgments and further explore whether there are gender differences in the neural mechanisms of facial attraction's influence on higher order moral decision-making. This will help us determine the extent to which we hold people responsible for those positive moral actions and reactions.