Infection detection in faces: Children's development of pathogen avoidance.

This study examined the development of children's avoidance and recognition of sickness using face photos from people with natural, acute, contagious illness. In a U.S. sample of fifty-seven 4- to 5-year-olds (46% male, 70% White), fifty-two 8- to 9-year-olds (26% male, 62% White), and 51 adults (59% male, 61% White), children and adults avoided and recognized sick faces (ds ranged from 0.38 to 2.26). Both avoidance and recognition improved with age. Interestingly, 4- to 5-year-olds' avoidance of sick faces positively correlated with their recognition, suggesting stable individual differences in these emerging skills. Together, these findings are consistent with a hypothesized immature but functioning and flexible behavioral immune system emerging early in development. Characterizing children's sickness perception may help design interventions to improve health.

Emerging Adults Mirror Infants' Emotions and Yawns.

Infants' nonverbal expressions-a broad smile or a sharp cry-are powerful at eliciting reactions. Although parents' reactions to their own infants' expressions are relatively well understood, here we studied whether adults more generally exhibit behavioral and physiological reactions to unfamiliar infants producing various expressions. We recruited U.S. emerging adults (N = 84) prior to parenthood, 18-25 years old, 68% women, ethnically (20% Hispanic/Latino) and racially (7% Asian, 13% Black, 1% Middle Eastern, 70% White, 8% multiracial) diverse. They observed four 80-s audio-video clips of unfamiliar 2- to 6-month-olds crying, smiling, yawning, and sitting calmly (emotionally neutral control). Each compilation video depicted 9 different infants (36 clips total). We found adults mirrored behaviorally and physiologically: more positive facial expressions to infants smiling, and more negative facial expressions and pupil dilation-indicating increases in arousal-to infants crying. Adults also yawned more and had more pupil dilation when observing infants yawning. Together, these findings suggest that even nonparent emerging adults are highly sensitive to unfamiliar infants' expressions, which they naturally "catch" (i.e., behaviorally and physiologically mirror), even without instructions. Such sensitivity may have-over the course of humans' evolutionary history-been selected for, to facilitate adults' processing of preverbal infants' expressions to meet their needs.

Validation of an open source, remote web-based eye-tracking method (WebGazer) for research in early childhood.

Measuring eye movements remotely via the participant's webcam promises to be an attractive methodological addition to in-person eye-tracking in the lab. However, there is a lack of systematic research comparing remote web-based eye-tracking with in-lab eye-tracking in young children. We report a multi-lab study that compared these two measures in an anticipatory looking task with toddlers using WebGazer.js and jsPsych. Results of our remotely tested sample of 18-27-month-old toddlers (N = 125) revealed that web-based eye-tracking successfully captured goal-based action predictions, although the proportion of the goal-directed anticipatory looking was lower compared to the in-lab sample (N = 70). As expected, attrition rate was substantially higher in the web-based (42%) than the in-lab sample (10%). Excluding trials based on visual inspection of the match of time-locked gaze coordinates and the participant's webcam video overlayed on the stimuli was an important preprocessing step to reduce noise in the data. We discuss the use of this remote web-based method in comparison with other current methodological innovations. Our study demonstrates that remote web-based eye-tracking can be a useful tool for testing toddlers, facilitating recruitment of larger and more diverse samples; a caveat to consider is the larger drop-out rate.

Behavioral and physiological sensitivity to natural sick faces.

The capacity to rapidly detect and avoid sick people may be adaptive. Given that faces are reliably available, as well as rapidly detected and processed, they may provide health information that influences social interaction. Prior studies used faces that were manipulated to appear sick (e.g., editing photos, inducing inflammatory response); however, responses to naturally sick faces remain largely unexplored. We tested whether adults detected subtle cues of genuine, acute, potentially contagious illness in face photos compared to the same individuals when healthy. We tracked illness symptoms and severity with the Sickness Questionnaire and Common Cold Questionnaire. We also checked that sick and healthy photos were matched on low-level features. We found that participants (N = 109) rated sick faces, compared to healthy faces, as sicker, more dangerous, and eliciting more unpleasant feelings. Participants (N = 90) rated sick faces as more likely to be avoided, more tired, and more negative in expression than healthy faces. In a passive-viewing eye-tracking task, participants (N = 50) looked longer at healthy than sick faces, especially the eye region, suggesting people may be more drawn to healthy conspecifics. When making approach-avoidance decisions, participants (N = 112) had greater pupil dilation to sick than healthy faces, and more pupil dilation was associated with greater avoidance, suggesting elevated arousal to threat. Across all experiments, participants' behaviors correlated with the degree of sickness, as reported by the face donors, suggesting a nuanced, fine-tuned sensitivity. Together, these findings suggest that humans may detect subtle threats of contagion from sick faces, which may facilitate illness avoidance. By better understanding how humans naturally avoid illness in conspecifics, we may identify what information is used and ultimately improve public health.

Superior Detection of Faces in Male Infants at 2 Months.

Females generally attend more to social information than males; however, little is known about the early development of these sex differences. With eye tracking, 2-month olds' (N = 101; 44 females) social orienting to faces was measured within four-item image arrays. Infants were more likely to detect human faces compared to objects, suggesting a functional face detection system. Unexpectedly, males looked longer at human faces than females, and only males looked faster and longer at human faces compared to objects. Females, in contrast, looked less at human faces relative to animal faces and objects, appearing socially disinterested. Notably, this is the first report of a male face detection advantage at any age. These findings suggest a unique stage in early infant social development.

Face detection in 2- to 6-month-old infants is influenced by gaze direction and species.

Humans detect faces efficiently from a young age. Face detection is critical for infants to identify and learn from relevant social stimuli in their environments. Faces with eye contact are an especially salient stimulus, and attention to the eyes in infancy is linked to the emergence of later sociality. Despite the importance of both of these early social skills-attending to faces and attending to the eyes-surprisingly little is known about how they interact. We used eye tracking to explore whether eye contact influences infants' face detection. Longitudinally, we examined 2-, 4-, and 6-month-olds' (N = 65) visual scanning of complex image arrays with human and animal faces varying in eye contact and head orientation. Across all ages, infants displayed superior detection of faces with eye contact; however, this effect varied as a function of species and head orientation. Infants were more attentive to human than animal faces and were more sensitive to eye and head orientation for human faces compared to animal faces. Unexpectedly, human faces with both averted heads and eyes received the most attention. This pattern may reflect the early emergence of gaze following-the ability to look where another individual looks-which begins to develop around this age. Infants may be especially interested in averted gaze faces, providing early scaffolding for joint attention. This study represents the first investigation to document infants' attention patterns to faces systematically varying in their attentional states. Together, these findings suggest that infants develop early, specialized functional conspecific face detection.

Face detection in infants and adults: Effects of orientation and color.

Humans rapidly locate and recognize human faces, even in complex environments. In the current study, we explored some of the social and perceptual features of faces that may contribute to this ability. We measured infant and adult attention to complex, heterogeneous image arrays containing human and animal faces. Arrays were upright or inverted 180° and in color or grayscale. Infants, aged 3-5 months (n = 51) and 10-11 months (n = 34), viewed 6-item arrays (Experiment 1), whereas adults (n = 120) searched 64-item arrays (Experiment 2). We found that 3- to 5-month-olds already displayed strong own-species biases in face detection-in attention capture, attention holding, and overall detection-suggesting a surprisingly early specialization for human face detection. Furthermore, this remarkable ability was robust, evident even when color and orientation were disrupted, and grew stronger with age. Interestingly, infants' face detection was reduced by low-level manipulations in a species-specific way, negatively affecting only animal face detection but not affecting human face detection. In contrast, adults' face detection efficiency was equally reduced by low-level manipulations across species, suggesting potential age differences in own-species face detection. For infants, social relevance (species) may play a more important role than low-level perceptual features, ensuring that infants attend to, connect with, and learn from the people around them. Efficient human face detection during infancy may reflect the uniqueness of own-species faces as a category, perhaps due to their social relevance.

Face Detection and the Development of Own-Species Bias in Infant Macaques.

In visually complex environments, numerous items compete for attention. Infants may exhibit attentional efficiency-privileged detection, attention capture, and holding-for face-like stimuli. However, it remains unknown when these biases develop and what role, if any, experience plays in this emerging skill. Here, nursery-reared infant macaques' (Macaca mulatta; n = 10) attention to faces in 10-item arrays of nonfaces was measured using eye tracking. With limited face experience, 3-week-old monkeys were more likely to detect faces and looked longer at faces compared to nonfaces, suggesting a robust face detection system. By 3 months, after peer exposure, infants looked faster to conspecific faces but not heterospecific faces, suggesting an own-species bias in face attention capture, consistent with perceptual attunement.

Efficient human face detection in infancy.

Adults detect conspecific faces more efficiently than heterospecific faces; however, the development of this own-species bias (OSB) remains unexplored. We tested whether 6- and 11-month-olds exhibit OSB in their attention to human and animal faces in complex visual displays with high perceptual load (25 images competing for attention). Infants (n = 48) and adults (n = 43) passively viewed arrays containing a face among 24 non-face distractors while we measured their gaze with remote eye tracking. While OSB is typically not observed until about 9 months, we found that, already by 6 months, human faces were more likely to be detected, were detected more quickly (attention capture), and received longer looks (attention holding) than animal faces. These data suggest that 6-month-olds already exhibit OSB in face detection efficiency, consistent with perceptual attunement. This specialization may reflect the biological importance of detecting conspecific faces, a foundational ability for early social interactions.

The development of facial identity discrimination through learned attention.

Learned attention models of perceptual discrimination predict that with age, sensitivity will increase for dimensions of stimuli useful for discrimination. We tested this prediction by examining the face dimensions 4- to 6-month-olds (n = 77), 9- to 12-month-olds (n = 66), and adults (n = 73) use for discriminating human, monkey, and sheep faces systematically varying in outer features (contour), inner features (eyes, mouth), or configuration (feature spacing). We controlled interindividual variability across species by varying faces within natural ranges and measured stimulus variability using computational image similarity. We found the most improvement with age in human face discrimination, and older participants discriminated more species and used more facial properties for discrimination, consistent with learned attention models. Older infants and adults discriminated human, monkey, and sheep faces; however, they used different facial properties for primates and sheep. Learned attention models may provide insight into the mechanisms underlying perceptual narrowing.