Testing detectability, attractivity, hedonic specificity, extractability, and robustness of colostrum odor-Toward an olfactory bioassay for human neonates.

Human milk odor is attractive and appetitive for human newborns. Here, we studied behavioral and heart-rate (HR) responses of 2-day-old neonates to the odor of human colostrum. To evaluate detection in two conditions of stimulus delivery, we first presented the odor of total colostrum against water. Second, the hedonic specificity of total colostrum odor was tested against vanilla odor. Third, we delivered only the fresh effluvium of colostrum separated from the colostrum matrix; the stability of this colostrum effluvium was then tested after deep congelation; finally, after sorptive extraction of fresh colostrum headspace, we assessed the activity of colostrum volatiles eluting from the gas chromatograph (GC). Regardless of the stimulus-delivery method, neonates displayed attraction reactions (HR decrease) as well as appetitive oral responses to the odor of total colostrum but not to vanilla odor. The effluvium separated from the fresh colostrum matrix remained appetitive but appeared labile under deep freezing. Finally, volatiles from fresh colostrum effluvium remained behaviorally active after GC elution, although at lower magnitude. In sum, fresh colostrum effluvium and its eluate elicited a consistent increase in newborns' oral activity (relative to water or vanilla), and they induced shallow HR decrease. Newborns' appetitive oral behavior was the most reproducible response criterion to the effluvium of colostrum. In conclusion, a set of unidentified volatile compounds from human colostrum is robust enough after extraction from the original matrix and chromatographic processing to continue eliciting appetitive responses in neonates, thus opening new directions to isolate and assay specific volatile molecules of colostrum.

Task-related modulation of facial expression processing: An FPVS-EEG study.

In the current study, we examined the role of task-related top-down mechanisms in the recognition of facial expressions. An expression of increasing intensity was displayed at a frequency of 1.5 Hz among the neutral faces of the same model that was displayed at a frequency of 12 Hz (i.e., 12 frames per second, with the expression occurring every eight frames). Twenty-two participants were asked either to recognize the emotion at the expression-specific frequency (1.5 Hz) or to perform an orthogonal task in separate blocks, while a scalp electroencephalogram (EEG) was recorded. A significant 1.5 Hz response emerged with the increase in expressive intensity over the medial occipital, right and left occipitotemporal, and centro-frontal regions. In these three regions, the magnitude of this response was greater when participants were involved in expression recognition, especially when the intensity of expression was low and ambiguous. Time-domain analysis revealed that engagement in the explicit recognition of facial expression caused a modulation of the response even before the onset of the expression over centro-frontal regions. The response was then amplified over the medial occipital and right and left occipitotemporal regions. Overall, the procedure developed in the present study allowed us to document different stages of the voluntary recognition of facial expressions, from detection to recognition, through the implementation of task-related top-down mechanisms that modulated the incoming information flow. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Horses discriminate human body odors between fear and joy contexts in a habituation-discrimination protocol.

Animals are widely believed to sense human emotions through smell. Chemoreception is the most primitive and ubiquitous sense, and brain regions responsible for processing smells are among the oldest structures in mammalian evolution. Thus, chemosignals might be involved in interspecies communication. The communication of emotions is essential for social interactions, but very few studies have clearly shown that animals can sense human emotions through smell. We used a habituation-discrimination protocol to test whether horses can discriminate between human odors produced while feeling fear vs. joy. Horses were presented with sweat odors of humans who reported feeling fear or joy while watching a horror movie or a comedy, respectively. A first odor was presented twice in successive trials (habituation), and then, the same odor and a novel odor were presented simultaneously (discrimination). The two odors were from the same human in the fear or joy condition; the experimenter and the observer were blinded to the condition. Horses sniffed the novel odor longer than the repeated odor, indicating they discriminated between human odors produced in fear and joy contexts. Moreover, differences in habituation speed and asymmetric nostril use according to odor suggest differences in the emotional processing of the two odors.

Asymmetrical responding to male versus female other-race categories in 9- to 12-month-old infants.

Faces can be categorized along various dimensions including gender or race, an ability developing in infancy. Infant categorization studies have focused on facial attributes in isolation, but the interaction between these attributes remains poorly understood. Experiment 1 examined gender categorization of other-race faces in 9- and 12-month-old White infants. Nine- and 12-month-olds were familiarized with Asian male or female faces, and tested with a novel exemplar from the familiarized category paired with a novel exemplar from a novel category. Both age groups showed novel category preferences for novel Asian female faces after familiarization with Asian male faces, but showed no novel category preference for novel Asian male faces after familiarization with Asian female faces. This categorization asymmetry was not due to a spontaneous preference hindering novel category reaction (Experiment 2), and both age groups displayed difficulty discriminating among male, but not female, other-race faces (Experiment 3). These results indicate that category formation for male other-race faces is mediated by categorical perception. Overall, the findings suggest that even by 12 months of age, infants are not fully able to form gender category representations of other-race faces, responding categorically to male, but not female, other-race faces.

A neural marker of rapid discrimination of facial expression in 3.5- and 7-month-old infants.

Infants' ability to discriminate facial expressions has been widely explored, but little is known about the rapid and automatic ability to discriminate a given expression against many others in a single experiment. Here we investigated the development of facial expression discrimination in infancy with fast periodic visual stimulation coupled with scalp electroencephalography (EEG). EEG was recorded in eighteen 3.5- and eighteen 7-month-old infants presented with a female face expressing disgust, happiness, or a neutral emotion (in different stimulation sequences) at a base stimulation frequency of 6 Hz. Pictures of the same individual expressing other emotions (either anger, disgust, fear, happiness, sadness, or neutrality, randomly and excluding the expression presented at the base frequency) were introduced every six stimuli (at 1 Hz). Frequency-domain analysis revealed an objective (i.e., at the predefined 1-Hz frequency and harmonics) expression-change brain response in both 3.5- and 7-month-olds, indicating the visual discrimination of various expressions from disgust, happiness and neutrality from these early ages. At 3.5 months, the responses to the discrimination from disgust and happiness expressions were located mainly on medial occipital sites, whereas a more lateral topography was found for the response to the discrimination from neutrality, suggesting that expression discrimination from an emotionally neutral face relies on distinct visual cues than discrimination from a disgust or happy face. Finally, expression discrimination from happiness was associated with a reduced activity over posterior areas and an additional response over central frontal scalp regions at 7 months as compared to 3.5 months. This result suggests developmental changes in the processing of happiness expressions as compared to negative/neutral ones within this age range.

Olfaction in the Multisensory Processing of Faces: A Narrative Review of the Influence of Human Body Odors.

A recent body of research has emerged regarding the interactions between olfaction and other sensory channels to process social information. The current review examines the influence of body odors on face perception, a core component of human social cognition. First, we review studies reporting how body odors interact with the perception of invariant facial information (i.e., identity, sex, attractiveness, trustworthiness, and dominance). Although we mainly focus on the influence of body odors based on axillary odor, we also review findings about specific steroids present in axillary sweat (i.e., androstenone, androstenol, androstadienone, and estratetraenol). We next survey the literature showing body odor influences on the perception of transient face properties, notably in discussing the role of body odors in facilitating or hindering the perception of emotional facial expression, in relation to competing frameworks of emotions. Finally, we discuss the developmental origins of these olfaction-to-vision influences, as an emerging literature indicates that odor cues strongly influence face perception in infants. Body odors with a high social relevance such as the odor emanating from the mother have a widespread influence on various aspects of face perception in infancy, including categorization of faces among other objects, face scanning behavior, or facial expression perception. We conclude by suggesting that the weight of olfaction might be especially strong in infancy, shaping social perception, especially in slow-maturing senses such as vision, and that this early tutoring function of olfaction spans all developmental stages to disambiguate a complex social environment by conveying key information for social interactions until adulthood.

When novelty prevails on familiarity: Visual biases for child versus infant faces in 3.5- to 12-month-olds.

The current study examined the influence of everyday perceptual experience with infant and child faces on the shaping of visual biases for faces in 3.5-, 6-, 9-, and 12-month-old infants. In Experiment 1, infants were presented with pairs of photographs of unfamiliar child and infant faces. Four groups with differential experience with infant and child faces were composed from parents' reports of daily exposure with infants and children (no experience, infant face experience, child face experience, and both infant and child face experience) to assess influence of experience on face preferences. Results showed that infants from all age groups displayed a bias for the novel category of faces in relation to their previous exposure to infant and child faces. In Experiment 2, this pattern of visual attention was reversed in infants presented with pictures of personally familiar child faces (i.e., older siblings) compared with unfamiliar infant faces, especially in older infants. These results suggest that allocation of attention for novelty can supersede familiarity biases for faces depending on experience and highlight that multiple factors drive infant visual behavior in responding to the social world.

Odor-driven face-like categorization in the human infant brain.

Understanding how the young infant brain starts to categorize the flurry of ambiguous sensory inputs coming in from its complex environment is of primary scientific interest. Here, we test the hypothesis that senses other than vision play a key role in initiating complex visual categorizations in 20 4-mo-old infants exposed either to a baseline odor or to their mother's odor while their electroencephalogram (EEG) is recorded. Various natural images of objects are presented at a 6-Hz rate (six images/second), with face-like object configurations of the same object categories (i.e., eliciting face pareidolia in adults) interleaved every sixth stimulus (i.e., 1 Hz). In the baseline odor context, a weak neural categorization response to face-like stimuli appears at 1 Hz in the EEG frequency spectrum over bilateral occipitotemporal regions. Critically, this face-like-selective response is magnified and becomes right lateralized in the presence of maternal body odor. This reveals that nonvisual cues systematically associated with human faces in the infant's experience shape the interpretation of face-like configurations as faces in the right hemisphere, dominant for face categorization. At the individual level, this intersensory influence is particularly effective when there is no trace of face-like categorization in the baseline odor context. These observations provide evidence for the early tuning of face-(like)-selective activity from multisensory inputs in the developing brain, suggesting that perceptual development integrates information across the senses for efficient category acquisition, with early maturing systems such as olfaction driving the acquisition of categories in later-developing systems such as vision.

Odor-evoked hedonic contexts influence the discrimination of facial expressions in the human brain.

The influence of odor valence on expressive-face perception remains unclear. Here, three "valenced" odor contexts (pleasant, unpleasant, control) were diffused while scalp electroencephalogram (EEG) was recorded in 18 participants presented with expressive faces alternating at a 6-Hz rate. One facial expression (happiness, disgust or neutrality) repeatedly arose every 6 face pictures to isolate its discrimination from other expressions at 1 Hz and harmonics in the EEG spectrum. The amplitude of the brain response to neutrality was larger in the pleasant vs. control odor context, and fewer electrodes responded in the unpleasant odor context. The number of responding electrodes was reduced for disgust in both odor contexts. The response to happiness was unchanged between odor conditions. Overall, these observations suggest that valenced odors influence the neural discrimination of facial expressions depending on both face and odor hedonic valence, especially for the emotionally ambiguous neutral expression.

Human neonates prefer colostrum to mature milk: Evidence for an olfactory bias toward the "initial milk"?

OBJECTIVES: Colostrum is the initial milk secretion which ingestion by neonates warrants their adaptive start in life. Colostrum is accordingly expected to be attractive to newborns. The present study aims to assess whether colostrum is olfactorily attractive for 2-day-old newborns when presented against mature milk or a control. METHODS: The head-orientation of waking newborns was videotaped in three experiments pairing the odors of: (a) colostrum (sampled on postpartum day 2, not from own mother) and mature milk (sampled on average on postpartum day 32, not from own mother) (n tested newborns = 15); (b) Colostrum and control (water; n = 9); and (c) Mature milk and control (n = 13). RESULTS: When facing the odors of colostrum and mature milk, the infants turned their nose significantly longer toward former (32.8 vs 17.7% of a 120-s test). When exposed to colostrum against the control, they responded in favor of colostrum (32.9 vs 16.6%). Finally, when the odor of mature milk was presented against the control, their response appeared undifferentiated (26.7 vs 28.6%). CONCLUSIONS: These results indicate that human newborns can olfactorily differentiate conspecific lacteal fluids sampled at different lactation stages. They prefer the odor of the mammary secretion - colostrum - collected at the lactation stage that best matches the postpartum age of their own mother. These results are discussed in the context of the earliest mother-infant chemo-communication. Coinciding maternal emission and offspring reception of chemosignals conveyed in colostrum may be part of the sensory precursors of attunement between mothers and infants.

Expertise for conspecific face individuation in the human brain.

Humans exhibit a marked specialization to process the most experienced facial morphologies. In particular, nonhuman primate faces are poorly discriminated compared to human faces in behavioral tasks. So far however, a clear and consistent marker that quantifies our expertise in human over monkey face discrimination directly from brain activity is lacking. Here, using scalp electroencephalography (EEG), we isolate a direct signature of individuation abilities for human and nonhuman (i.e., macaque faces) primate faces. Human or monkey faces were rapidly presented at a base rate of 12 Hz in upright or inverted orientations while participants performed an orthogonal behavioral task. In each stimulation sequence, eight face images of one individual were used as base stimuli, while images of other individuals were briefly introduced every 9th stimulus to quantify an identity-change response at 1.33 Hz and harmonics (i.e., integer multiples) in the EEG frequency spectrum. The brain response to upright human faces was twice as large as to monkey faces, and reduced following picture-plane inversion for human faces only. This reflects the disruption of high-level face identity discrimination developed for the canonical upright human face. No difference was observed between upright monkey faces and inverted human faces, suggesting non-expert visual processes for those two face formats associated with little experience. In addition, the size of the inversion effect for human, but not monkey faces, was predictive of the expertise effect (i.e., difference between upright human and monkey faces) at the individual level. This result suggests a selective ability to discriminate human faces that does not contribute to the individuation of other unexperienced face morphologies such as monkey faces. Overall, these findings indicate that human expertise for conspecific face discrimination can be isolated and quantified in individual human brains.

Preference for attractive faces is species-specific.

Studies on facial attractiveness in human adults, infants, and newborns have consistently reported a visual preference for faces rated as attractive compared with faces rated as unattractive. Biological accounts of facial attractiveness have typically presented such preferences as arising from adaptations for mate choice or as by-products of general sensory bias. In this cross-species study, we examined whether explicit ratings of attractiveness made by human judges would predict implicit visual preferences in other humans and also in rhesus macaques and, if they do, whether such preferences would extend beyond conspecific faces. Results showed that human ratings of attractiveness can predict implicit preferences in nonhuman primates (macaque monkeys; Macaca mulatta). However, we also found a species-specific effect of face attractiveness in which humans showed a visual preference for human faces (but not macaque faces) rated as attractive, and macaques displayed a visual preference for macaque faces (but not human faces) rated as attractive. Overall, the findings suggest that attentional bias toward attractive faces arises neither from an exclusive operation of mate choice adaptation mechanisms nor from the sole influence of a general sensory bias, but rather reflects their interaction. The influence of a general sensory bias may be modulated by the categorization of a face as conspecific or heterospecific, leading to species-specific preference for attractive faces. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Development of Preferences for Differently Aged Faces of Different Races.

Children's experiences with differently aged faces changes in the course of development. During infancy, most faces encountered are adult, however as children mature, exposure to child faces becomes more extensive. Does this change in experience influence preference for differently aged faces? The preferences of children for adult versus child, and adult versus infant faces were investigated. Caucasian 3- to 6-year-olds and adults were presented with adult/child and adult/infant face pairs which were either Caucasian or Asian (race consistent within pairs). Younger children (3 to 4 years) preferred adults over children, whereas older children (5 to 6 years) preferred children over adults. This preference was only detected for Caucasian faces. These data support a "here and now" model of the development of face age processing from infancy to childhood. In particular, the findings suggest that growing experience with peers influences age preferences and that race impacts on these preferences. In contrast, adults preferred infants and children over adults when the faces were Caucasian or Asian, suggesting an increasing influence of a baby schema, and a decreasing influence of race. The different preferences of younger children, older children, and adults also suggest discontinuity and the possibility of different mechanisms at work during different developmental periods.

An adult face bias in infants that is modulated by face race.

The visual preferences of infants for adult versus infant faces were investigated. Caucasian 3.5- and 6-month-olds were presented with Caucasian adult versus infant face pairs and Asian adult versus infant face pairs, in both upright and inverted orientations. Both age groups showed a visual preference for upright adult over infant faces when the faces were Caucasian, but not when they were Asian. The preference is unlikely to have arisen because of low-level perceptual features because: (1) no preference was observed for the inverted stimuli, (2) no differences were observed in adult similarity ratings of the upright infant-adult face pairs from the two races, and (3) no differences between the infant and adult faces were observed across races in an image-based analysis of salience. The findings are discussed in terms of the social attributes of faces that are learned from experience and what this implies for developmental accounts of a recognition advantage for adult faces in particular and models of face processing more generally.

Preference for facial averageness: Evidence for a common mechanism in human and macaque infants.

Human adults and infants show a preference for average faces, which could stem from a general processing mechanism and may be shared among primates. However, little is known about preference for facial averageness in monkeys. We used a comparative developmental approach and eye-tracking methodology to assess visual attention in human and macaque infants to faces naturally varying in their distance from a prototypical face. In Experiment 1, we examined the preference for faces relatively close to or far from the prototype in 12-month-old human infants with human adult female faces. Infants preferred faces closer to the average than faces farther from it. In Experiment 2, we measured the looking time of 3-month-old rhesus macaques (Macaca mulatta) viewing macaque faces varying in their distance from the prototype. Like human infants, macaque infants looked longer to faces closer to the average. In Experiments 3 and 4, both species were presented with unfamiliar categories of faces (i.e., macaque infants tested with adult macaque faces; human infants and adults tested with infant macaque faces) and showed no prototype preferences, suggesting that the prototypicality effect is experience-dependent. Overall, the findings suggest a common processing mechanism across species, leading to averageness preferences in primates.

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.

Development of category formation for faces differing by age in 9- to 12-month-olds: An effect of experience with infant faces.

We examined category formation for faces differing in age in 9- and 12-month-olds, and the influence of exposure to infant faces on such ability. Infants were familiarized with adult or infant faces, and then tested with a novel exemplar from the familiarized category paired with a novel exemplar from a novel category (Experiment 1). Both age groups formed discrete categories of adult and infant faces, but exposure to infant faces in everyday life did not modulate performance. The same task was conducted with child versus infant faces (Experiment 2). Whereas 9-month-olds preferred infant faces after familiarization with child faces, but not child faces after familiarization with infant faces, 12-month-olds formed discrete categories of child and infant faces. Moreover, more exposure to infant faces correlated with higher novel category preference scores when infants were familiarized with infant faces in 12-month-olds, but not 9-month-olds. The 9-month-old asymmetry did not reflect spontaneous preference for infant over child faces (Experiment 3). These findings indicate that 9- and 12-month-olds can form age-based categories of faces. The ability of 12-month-olds to form separate child and infant categories suggests that they have a more exclusive representation of face age, one that may be influenced by prior experience with infant faces.

Can human eyes prevent perceptual narrowing for monkey faces in human infants?

Perceptual narrowing has been observed in human infants for monkey faces: 6-month-olds can discriminate between them, whereas older infants from 9 months of age display difficulty discriminating between them. The difficulty infants from 9 months have processing monkey faces has not been clearly identified. It could be due to the structural characteristics of monkey faces, particularly the key facial features that differ from human faces. The current study aimed to investigate whether the information conveyed by the eyes is of importance. We examined whether the presence of Caucasian human eyes in monkey faces allows recognition to be maintained in 6-month-olds and facilitates recognition in 9- and 12-month-olds. Our results revealed that the presence of human eyes in monkey faces maintains recognition for those faces at 6 months of age and partially facilitates recognition of those faces at 9 months of age, but not at 12 months of age. The findings are interpreted in the context of perceptual narrowing and suggest that the attenuation of processing of other-species faces is not reversed by the presence of human eyes.

The eye-size illusion: psychophysical characteristics, generality, and relation to holistic face processing.

Rakover [(2011). In Y. H. Zhang (Ed.), Advances in face image analysis: Techniques and technologies (pp. 316-333). Hershey, PA: IGI Global] observed a novel eye-size illusion: when increasing the size of a face but keeping the size of its eyes unchanged, the eyes are perceived to be smaller than in the original face. Here, we systematically manipulated the face size and found that the magnitude of this illusion linearly changed as a function of the face frame size (experiment 1). Additionally, the same magnitude of an illusion was observed for the perception of the size of the mouth when we changed the face frame but kept the mouth size constant (experiment 2). Further, when the faces and eyes were presented upside down, the magnitude of the illusion was significantly reduced in both Chinese participants (experiment 3) and Caucasian participants (experiment 4). The results suggest that the perception of eye or mouth size occurs in the relational context of the whole face; and when the face is inverted, thereby disrupting holistic processing, the magnitude of the illusion is reduced. We therefore suggest that holistic processing is involved in producing the illusion.