An ERP study of emotional face processing in the adult and infant brain

To examine the ontogeny of emotional face processing, event-related potentials (ERPs) were recorded from adults and 7-month-old infants while viewing pictures of fearful, happy, and neutral faces. Face-sensitive ERPs at occipital-temporal scalp regions differentiated between fearful and neutral/happy faces in both adults (N170 was larger for fear) and infants (P400 was larger for fear). Behavioral measures showed no overt attentional bias toward fearful faces in adults, but in infants, the duration of the first fixation was longer for fearful than happy faces. Together, these results suggest that the neural systems underlying the differential processing of fearful and happy/neutral faces are functional early in life, and that affective factors may play an important role in modulating infants' face processing.     

Recognition of facial expressions by seven-month-old infants

3 experiments examined 7-month-old infants' ability to discriminate the facial expressions of happy vs. fear. Experiment 1 revealed that infants demonstrated discrimination of happy vs. fear expressions when posed by a single model but that this discrimination was affected by the order of stimulus presentation. In experiment 2 infants were shown 2 models posing the happing and fearful expressions and did not demonstrate generalization of the discrimination of happy versus fear across these models. The third and main experiment varied the test procedure. Here, infants demonstrated reliable generalized discrimination of the 2 expressions across different models. As in experiment 1, however, these results were constrained by the order in which the stimuli were presented. These consistent order effects were not due to the initial salience of the 2 expressions but, instead, appeared to reflect differential rates of habituation to happy vs. fear expressions.     

Intermodal Perception of Happy and Angry Expressive Behaviors by Seven-Month-Old Infants

2 studies were conducted to examine the roles of facial motion and temporal correspondences in the intermodal perception of happy and angry expressive events. 7-month-old infants saw 2 video facial expressions and heard a single vocal expression characteristic of one of the facial expressions. Infants saw either a normally lighted face (fully illuminated condition) or a moving dot display of a face (point light condition). In Study 1, one woman expressed the affects vocally, another woman expressed the affects facially, and what they said also differed. Infants in the point light condition showed a reliable preference for the affectively concordant displays, while infants in the fully illuminated condition showed no preference for the affectively concordant display. In a second study, the visual and vocal displays were produced by a single individual on one occasion and were presented to infants 5 sec out of synchrony. Infants in both conditions looked longer at the affectively concordant displays. The results of the 2 studies indicate that infants can discriminate happy and angry affective expressions on the basis of motion information, and that the temporal correspondences unifying these affective events may be affect-specific rhythms.     

Electrophysiological correlates of infant recognition memory

Event-Related Potentials were recorded from 6-month-old infants in order to examine the electrophysiological correlates of recognition memory. In 1 study, infants were shown 1 face briefly, followed by the same face presented with high probability, and a novel face presented with low probability. 2 components were observed that distinguished between the novel and familiar events. Differences between these components in latency, polarity, and scalp topography led to the suggestion that 2 processes were involved in recognizing the stimuli. In a second study infants were again presented with 1 face briefly, followed by the same face and a novel face presented with equal probability. 1 component at central scalp distinguished between the novel and familiar events. In a third study, infants were simply presented with 2 previously unseen faces equally often. Infants responded as if the faces were identical, suggesting that previous experience with 1 stimulus directs infants' attention to the novel stimulus during the test portion of the task. The extent to which the observed responses reflect the updating of working memory is discussed, as is the extent to which infants' electrophysiological response to stimulus novelty and uncertainty resembles the adult's.     

Generalized Discrimination of Positive Facial Expressions by Seven- and Ten-Month-Old Infants

The ability of 7- and 10-month-old infants to generalize their discrimination of facial expressions lacking featural consistency was investigated in a series of 4 experiments. Infants were habituated to models posing either prototypically positive displays (e.g., happy expressions) or positive expression blends (e.g., mock surprise). They were then tested for their ability to recognize a positive expression on the face of a novel model and to discriminate positive and negative facial expressions. Only in Experiment 1, in which infants were familiarized to a mix of happy and surprised facial expressions, did 10-month-olds demonstrate generalized discrimination of positive affect. When positive blends or happy expressions alone served as familiarization stimuli, both 7- and 10-month-old infants failed to dishabituate to a change in affective tone. 7-month-olds, in particular, showed consistent recovery of looking to the introduction of novel models. The pattern of results suggests that it is not until sometime after 7 months of age that dependence on the presence of expression-specific features for affect recognition and discrimination diminishes. By 10 months of age, however, infants are beginning to recognize the affective similarity of familiar positive facial expressions.     

Affective Influences on Startle in Five-Month-Old Infants: Reactions to Facial Expressions of Emotion

Convergent methodologies from studies of fear-potentiated startle in animals and studies of affective modulation of reflex blinks in humans were adapted in order to investigate infants' sensitivity to affective information conveyed by facial expressions of emotion. While 5-month-old infants viewed photographic slides of faces posed in happy, neutral, or angry expressions, a brief acoustic noise burst was presented to elicit the blink component of human startle. Blink size was augmented during the viewing of angry expressions and reduced during happy expressions. Infants did not show marked changes in behavioral reactions to the positive, neutral, and negative slides, although motor activity was slightly reduced during negative slides. Results suggest that, by 5 months, infants react to affective information conveyed by unfamiliar human faces. Potential mechanisms mediating the influence of affective stimuli on reflex excitability are considered.     

The role of person familiarity in young infants' perception of emotional expressions

This research investigated the role of person familiarity in the ability of 3.5-month-old infants to recognize emotional expressions. Infants (N = 72) were presented simultaneously with two filmed facial expressions, happy and sad, accompanied by a single vocal expression that was concordant with one of the two facial expressions. Infants' looking preferences and facial expressions were coded. Results indicated that when the emotional expressions were portrayed by each infant's own mother, infants looked significantly longer toward the facial expressions that were accompanied by affectively matching vocal expressions. Infants who were presented with emotional expressions of an unfamiliar woman did not. Even when a brief delay was inserted between the presentation of facial and vocal expressions, infants who were presented with emotional expressions of their own mothers looked longer at the facial expression that was sound specified, indicating that some factor other than temporal synchrony guided their looking preferences. When infants viewed the films of their own mothers, they were more interactive and expressed more positive and less negative affect. Moreover, infants produced a greater number of full and bright smiles when the sound-specified emotion was "happy," and particularly when they viewed the happy expressions of their own mothers. The average duration of negative affect was significantly longer for infants who observed the unfamiliar woman than for those who observed their own mothers. These results show that when more contextual information-that is, person familiarity-was available, infants as young as 3.5 months of age recognized happy and sad expressions. These findings suggest that in the early stages of development, infants are sensitive to contextual information that potentially facilitates some of the meaning of others' emotional expressions.     

Parsing Items into Separate Categories: Developmental Change in Infant Categorization

Three experiments report developmental change in infants' tendency to parse exemplars into separate categories. In Experiment 1, a familiarization-novelty preference procedure was used. Fifty-four 4-, 7-, and 10-month-old infants were familiarized with members of two basic-level animal categories (cats and horses) and tested with novel members of the familiarized categories and with members of a third category (dogs). In Experiment 2, a habituation-dishabituation procedure was used. Forty-eight 7- and 10-month-old infants were habituated to examples of both male and female faces and tested with novel gender-typical and gender-ambiguous faces. In both experiments, 10-month-old infants appeared to form differentiated categories, whereas younger infants formed a single category to include the range of items presented during familiarization. Experiment 3 ruled out a priori stimulus preferences as an explanation for the 10-month findings in Experiment 2.     

Do infants see emotional expressions in static faces?

To determine whether young infants discriminate photographs of different emotions on an affect-relevant basis or on the basis of isolated features unrelated to emotion, groups of 17-, 23-, and 29-week-olds were habituated to slides of 8 women posing either Toothy Angry, Nontoothy Angry, or Nontoothy Smiling facial expressions and were then shown 2 new women in the familiarized expression and in a novel Toothy Smiling expression. At all 3 ages, recovery to the novel Toothy Smiling faces occurred only after habituation to Nontoothy faces (whether smiling or angry), not after habituation to Toothy Angry faces, indicating that infants had been responsive to nonspecific features of the photographs (presence or absence of bared teeth) rather than to affectively relevant configurations of features. In a second experiment, 2 older age groups (35 and 41 weeks) also proved to be insensitive to affect-related aspects of still faces, though more so for angry than for happy expressions. It is suggested that the young infant's difficulty in extracting emotional information from static stimuli may be attributable to the absence of the critical invariants (dynamic, multimodally specified) that characterize naturalistic expressions of emotion.     

Developmental changes in the scanning of faces by young infants.

6 1-month-old infants and 6 2-month-old infants each viewed 3 faces (his mother's, a strange woman's, and a strange man's) while his eye movements were recorded by corneal photography. The 1-month-olds fixated away from the faces most of the time, and they looked at their mothers even less often than at the strangers. When they did fixate a face, they usually chose a limited portion of the perimeter. By constrast, 2-month-olds fixated the faces most of the time, looked at more features, and were more likely to look at internal features, especially the eyes. This scanning resembles that reported previously for 2-dimensional shapes, although in some respects it appears unique to faces.     

Intermodal Perception of Adult and Child Faces and Voices by Infants

This research investigated the ability of 4- and 7-month-old infants to match unfamiliar, dynamic faces and voices on the basis of age or maturity. In Experiment 1, infants received videotaped trials of an adult and a child of the same gender, side by side, speaking a nursery rhyme in synchrony with one another. The voice to one and then the other face was played in synchrony with the movements of both faces in a random order across 12 trials. On one block of 6 trials a man and a boy were presented, and on the other block a woman and a girl. Results indicated significant matching of the faces and voices at both ages, and the infant's prior experience with children appeared to facilitate matching at 7 months. Further, a visual preference for the children's faces was found. Experiment 2 assessed matching to the same events by 7-month-olds, only with the faces inverted. Results indicated no evidence of matching; however, the visual preference for the children's faces was replicated. Together, the findings suggest that infants are able to detect invariant intermodal relations specifying the age or maturity of a person's face and voice. This matching was most likely based on information that was degraded by inverting the faces, including invariant relations between the sound of the voice and configurational aspects of the face, or between temporal aspects of the voice and the relative motion of facial features.     

Infants' perception of dynamic affective expressions: do infants distinguish specific expressions?

Seven-month-old infants' perception of positive (happy, interested) and negative (angry, sad) affective expressions was investigated using a preferential looking procedure (n = 20 in each of 6 conditions). The infants saw two videotaped facial expressions and heard a single vocal expression concordant with one of the facial expressions. The voice on the soundtrack was played 5 s out of synchrony with the ongoing affective visual display. Infants participated in one of six conditions (all possible pairs of the four expressive events). Infants' visual fixations to the affectively concordant and affectively discordant displays were recorded. Infants looked longer at the affectively concordant displays than at the affectively discordant displays in all conditions except the happy/sad and interested/sad conditions. For these two comparisons, facial discrimination was demonstrated by the infants' preferential looking at happy and interested expressions compared to the sad expression. Thus, 7-month-old infants discriminate among happy, interested, angry, and sad expressions, demonstrating differentiation among specific, dynamic expressions. The results are discussed in terms of the information specifying facial and vocal affect and the possible role of familiarity in learning to differentiate among affective expressions during infancy.     

Object Permanence in Young Infants: Further Evidence

Recent evidence suggests that 4.5- and even 3.5-month-old infants realize that objects continue to exist when hidden. The goal of the present experiments was to obtain converging evidence of object permanence in young infants. Experiments were conducted using paradigms previously used to demonstrate object permanence in 5.5-month-old infants and 6.5-month-old infants. In one experiment, 3.5-month-old infants watched a short or a tall carrot slide along a track. The track's center was hidden by a screen with a large window in its upper half. The short carrot was shorter than the window's lower edge and so did not appear in the window when passing behind the screen; the tall carrot was taller than the window's lower edge and hence should have appeared in the window but did not. The infants looked reliably longer at the tall than at the short carrot event, suggesting that they (a) represented the existence, height, and trajectory of each carrot behind the screen and (b) expected the tall carrot to appear in the screen window and were surprised that it did not. Control trials supported this interpretation. In another experiment, 4.0-month-old infants saw a toy car roll along a track that was partly hidden by a screen. A large toy mouse was placed behind the screen, either on top or in back of the track. The female infants looked reliably longer when the mouse stood on top as opposed to in back of the track, suggesting that they (a) represented the existence and trajectory of the car behind the screen, (b) represented the existence and location of the mouse behind the screen, and (c) were surprised to see the car reappear from behind the screen when the mouse stood in its path. A second experiment supported this interpretation. The results of these experiments provide further evidence that infants aged 3.5 months and older are able to represent and to reason about hidden objects.     

Hemispheric asymmetry in a face discrimination task in infants

A right-hemisphere advantage in a mother's face recognition task in infants aged between 4 and 10 months was found to exist by de Schonen, Gil de Diaz, and Mathivet. The present study was designed to test (a) whether the right-hemisphere advantage would still prevail if the task requirements were different from those in the previous study, and (b) whether any information was communicated from one hemisphere to the other. 18-42-week-old infants were presented with an operant conditioning situation where they had to discriminate between their mother's and a stranger's face within one visual hemifield. Transfer of learning from one visual hemifield to the other was also measured. The results confirm the existence of a right-hemisphere advantage in discriminating between face stimuli. This advantage was weaker in the female than in the male population. No hemispheric transfer of learning was observed to occur.     

Developmental change in the ERP responses to familiar faces in toddlers with autism spectrum disorders versus typical development

Individuals with autism spectrum disorder (ASD) show differences in face processing abilities from early in development. To examine whether these differences reflect an atypical versus delayed developmental trajectory, neural responses to familiar and unfamiliar faces in twenty-four 18- to 47-month-old children with ASD were compared with responses of thirty-two 12- to 30-month-old typically developing children. Results of 2 experiments revealed that neural responses to faces in children with ASD resembled those observed in younger typically developing children, suggesting delayed development. Electrophysiological responses to faces were also related to parent report of adaptive social behaviors for both children with ASD and typical development. Slower development of the face processing system in ASD may be related to reduced self-directed "expected" experience with faces in early development.     

Neural Processing of Eye Gaze and Threat‐Related Emotional Facial Expressions in Infancy

Combined with emotional expressions, eye gaze can provide essential information to indicate threat in the environment. The current study assessed the effects of eye gaze direction on infants’ neural processing of fearful and angry faces. Event‐related potentials were recorded from thirteen 7‐month‐old infants. Two face‐sensitive posterior components, the N290 and P400, as well as a frontocentral negative component (Nc), indicating attentional arousal, were sensitive to eye gaze direction and emotion. A larger Nc was observed for angry faces with direct compared to averted eye gaze. Fearful faces elicited a larger N290 than angry faces, whereas angry faces elicited a more prominent P400 regardless of eye gaze direction. The findings are discussed in terms of early social cognitive and neural development.     

The Effects of Parental Behavior on Infants' Neural Processing of Emotion Expressions

Infants become sensitive to emotion expressions early in the 1st year and such sensitivity is likely crucial for social development and adaptation. Social interactions with primary caregivers may play a key role in the development of this complex ability. This study aimed to investigate how variations in parenting behavior affect infants' neural responses to emotional faces. Event‐related potentials (ERPs) to emotional faces were recorded from 40 healthy 7‐month‐old infants (24 males). Parental behavior was assessed and coded using the Emotional Availability Scales during free‐play interaction. Sensitive parenting was associated with increased amplitudes to positive facial expressions on the face‐sensitive ERP component, the negative central. Findings are discussed in relation to the interactive mechanisms influencing how infants neurally encode positive emotions.     

Developmental Change in Infant Categorization: The Perception of Correlations among Facial Features

Previous studies indicated that the ability to detect correlations among attributes emerges between 7 and 10 months of age. In the present study, the generality of this developmental transition was examined. Using an infant-control habituation procedure, 48 7- and 10-month-old infants were tested for the perception of correlations among basic facial features. The developmental effects were replicated. Only the 10-month-old infants demonstrated their sensitivity to the pattern of correlation by generalizing to a novel face that preserved the experienced pattern of correlation, while showing increased attention to a face in which the pattern of correlation was violated. 7-month-old infants generalized to both test stimuli containing familiar features, regardless of the status of the correlation. Implications for face perception and the processing of categorical information are discussed.     

Infants' Perception of Emotion From Body Movements

Adults recognize emotions conveyed by bodies with comparable accuracy to facial emotions. However, no prior study has explored infants' perception of body emotions. In Experiment 1, 6.5‐month‐olds (n = 32) preferred happy over neutral actions of actors with covered faces in upright but not inverted silent videos. In Experiment 2, infants (n = 32) matched happy and angry videos to corresponding vocalizations when the videos were upright but not when they were inverted. Experiment 3 (n = 16) demonstrated that infants' performance in Experiment 2 was not driven by information from the covered face and head. Thus, young infants are sensitive to emotions conveyed by bodies and match them to affective vocalizations, indicating sophisticated emotion processing capabilities early in life.