Whether passing briefly on the street, sitting opposite one another on a commuter train, or engaging in extensive conversation in a business meeting, we are consistently in the position of forming impressions of other people based on limited amounts of information. The ability to extract meaningful information about a person in our daily encounters may often be taken for granted. The rich cognitive complexity that forms the architecture for our capacity to perceive others often escapes our conscious awareness, emerging only as intuitive hunches or “gut feelings.” But although this sense of intuition leaves us with the feeling that our impressions of others are rough, ambiguous, and subjective, a growing body of evidence shows that our impressions of others can, in some cases, be fairly accurate. The current investigation elucidates one of these common hunches by providing empirical evidence for a surprising effect within interpersonal perception: the ability to accurately infer individuals' religious group membership from nothing more than their faces.
The human face is among the richest of all social stimuli in the human environment 
. Not only does the face provide obvious cues to emotional expressions and intentions in its dynamic movements 
, even in its static form it can provide information about a variety of traits: personality attributes 
, individual identity 
, and group membership 
. The last of these, group membership, is presently one of the best explored areas within which the face and its features can provide relevant and important information. We effortlessly and automatically extract information about individuals' sex and gender, race, and relative age from their faces 
. Systematic investigations of the features involved in accurately perceiving an individual's gender, for example, have shown that multiple features convey information about whether a person is a man or a woman. Among these, several have been shown to be of key importance: the hair, the shape of the face, the eyes and brows, and even the mouth 
. Similarly, although fewer empirical data have been presented for the facial cues that distinguish different racial groups, hair is known to be an important cue in some race judgments 
, and variation among race-distinctive features can have important effects upon individuals' perceptions 
Whereas the study of cues leading to the accurate perception of age, race and gender has led to important insights about the ability to perceive social information from nonverbal and appearance cues, the knowledge that can be gleaned from studying these categories may be limited by the general obviousness of the distinctions between the groups defined along those axes (e.g., men versus women for gender). The study of groups whose physical markers are less obvious may provide a unique window into the processes of social perception.
One fairly perceptually ambiguous social category is that of sexual orientation. Recent work has shown that the face provides information that allows individuals to judge others' sexual orientations with accuracy that is significantly higher than chance guessing 
. These judgments can be accurately derived even when perceivers see the faces of gay and straight men and women for small fractions of a second 
. Since this accuracy does not increase when perceivers are given more time to study the faces and because the brief perception of gay and straight faces has been shown to influence the processing of associated stereotypes, the perception of sexual orientation appears to occur automatically, just as is observed for the perception of age, race, and sex 
. Subsequent study of the facial features that support the accuracy of these judgments has revealed that multiple cues express information about individuals' sexual orientations that can be used for accurate perception: the hair, eyes, and mouth; but these cues differ in the extent to which perceivers are aware of their use 
. Perceivers appear to know that judgments of hairstyles allow them to accurately perceive others' sexual orientations but seem not to know that their judgments based on just the eyes or mouth also allow them to perceive sexual orientation accurately 
. These data suggest that information about social group membership may be expressed simultaneously from multiple cues for use by both explicit and implicit perceptual processes—an insight that likely may not have been gained from studying groups for whom perception is obvious because the task of judging group membership from individual features might be too easy.
Similar to judgments of sexual orientation, there are other groups for whom individuals hold an intuitive sense of their ability to extract relevant information from nonverbal cues. One such intuition is the claim by some members of the Mormon religious faith (formally known as the Church of Jesus Christ of Latter Day Saints) that they can reliably discern who is Mormon and who is not Mormon from their appearance. In a recent study, we found evidence that this may be true 
. Mormons and non-Mormons who passively observed the faces of both ingroup and outgroup members showed significantly better recognition memory for individuals belonging to their ingroup than they did for individuals belonging to their outgroup, similar to ingroup memory advantage effects commonly found for age 
, race 
, and gender 
. Moreover, when perceivers were asked to explicitly indicate which of the faces they believed to be Mormon and non-Mormon, they were able to accurately categorize the individuals at rates significantly better than chance guessing. This was true for both Mormon and non-Mormon perceivers, living in both Mormon-populous and Mormon-scarce environments; but Mormons were more accurate than non-Mormons in making the distinction.
That Mormons and non-Mormons can be accurately categorized from their faces suggests that there must be a salient perceptual cue distinguishing the two groups. One explanation offered for the distinction between Mormons and non-Mormons is differences in expressed spirituality. For example, one Mormon woman described her experience with this phenomenon on her personal web-log with the following anecdote:
I ran into the TA whom I asked to speak on the Holy Ghost for my baptism. I was very excited to see him. There was this sense of “glow” from him, which I heard about many times yet never understood, like a “Mormon Radar.” But I saw it for the first time and I finally understood what it is. It is the Spirit! 
The belief that divine annunciation distinguishes Mormons from non-Mormons notwithstanding, other explanations may exist. For instance, Mormons are known to significantly differ from non-Mormons in their overall health, as measured by life expectancy 
. Owing largely to their strict, substance-free lifestyle (which includes both illegal and legal recreational substances, such as alcohol, tobacco, and caffeine), Mormons are considered one of the healthiest populations of individuals in the United States 
. Mormons show lower cancer rates 
and overall lower mortality rates as compared to non-Mormons 
. These differences are believed to be the effect of Mormons' substance-free lifestyle, routine health behaviors (i.e., exercise and well-balanced diet), early marriage, and regular church attendance 
. Indeed, a 24-year longitudinal study found Mormons to have a life expectancy rate 6–10 years longer than that of non-Mormon controls 
. Early Church leaders, upon subjective observation of the Mormons' increased health advantage, also ascribed this distinction to divine influence:
The gift of the Holy Ghost … develops beauty of person, form and features. It tends to health, vigor, animation, and social feeling [30, p. 101].
Given that Mormons and non-Mormons do differ in their actual health and that individuals have subjectively reported the ability to read a difference between Mormons and non-Mormons from appearance cues, it seemed that the physical cue distinguishing Mormons and non-Mormons in their appearance may be visible signs of differences in health. We tested this hypothesis in the present work.
In light of recent research, it is not improbable that health could distinguish Mormons from non-Mormons. Jones et al., for instance, showed that judgments of health from high-resolution photos of patches of facial skin were related to perceivers' judgments of overall facial attractiveness 
. Similarly, Roberts et al. found that perceptions of health from facial skin were related to individuals' actual health via genetic measures of immunological strength 
. Thus, facial skin appears to carry valid cues to individuals' actual health 
. Another facial cue associated with accurate judgments of individuals' health is their facial adiposity 
. Specifically, perceivers' judgments about an individual's apparent body weight from photos of only their faces significantly corresponded to their actual cardiovascular health, as measured by body-mass index, frequency and duration of respiratory illnesses, frequency of antibiotics use, and other measures of cardiovascular health 
. In addition, some discussions of the components underlying differences in facial attractiveness have hypothesized that facial attractiveness advertises individuals' health 
, and that one key quality responsible for this is symmetry across the face's vertical axis 
If differences in health really are responsible for distinguishing Mormons' and non-Mormons' faces, it is likely that these cues are very subtle. Indeed, in the recognition memory studies reported above, participants expressed no awareness that the task concerned Mormons and non-Mormons 
. This means that subtle differences in the faces of the two groups were likely extracted non-consciously in order to systematically affect the perceivers' later recognitions of the faces. Indeed, in that work we found that both environmentally- and experimentally-induced group salience worked to non-consciously prime perceivers to encode the faces according to religious group membership.
Elucidation of how perceivers are able to make these categorizations would therefore provide an interesting and informative illustration of the subtle manner by which we are able to incorporate basic perceptual cues into the cognitive-perceptual stream to support the construction of complex social judgments, such as social categorization. Moreover, that such a subtle distinction can exist and be perceived among an obscure set of targets would suggest that the cognitive machinery used for social categorization is quite flexible, permitting the application of basic perceptual distinctions to discriminating novel social groups as they are encountered by the cognitive system.
The present work therefore attempts to deconstruct the means by which perceivers extract information about Mormon and non-Mormon group membership from faces. In doing so, we first extend research demonstrating that individuals can make accurate judgments of Mormon/non-Mormon group membership from full faces in Study1 to show that participants are unaware of their accuracy in making these judgments. In Study 2, we then systematically test the physical features of the face that might potentially be involved in judging Mormon/non-Mormon group membership to determine which provide legible cues and which do not. Study 3 then specifically tests the hypotheses that the difference between Mormons' and non-Mormons' faces is based on perceptions of spirituality and health. Finally, Study 4 focuses specifically on the aspects of the face that have been previously found to express information about health and tests various statistical models to account for how these cues may lead to accurate judgments of Mormon/non-Mormon group membership.