Biological bases of face preference in 6-week-old infants

Six-week-old infants (N =40) who started the experiment in either a calm or crying state, received sucrose from an experimenter, while in eye contact with her. Sucrose was delivered either by syringe or on a pacifier. After 3.5 min., the experimenter retired, the mother came into the test room and placed her infant over her shoulder en face with a video camera. The experimenter and a confederate, both dressed identically, sat in front of and slightly to either side of the infant and the infant could choose to look at either experimenter. To minimize position bias, experimenters switched sides every 30 sec. To maintain a stable level of infant attention, they simultaneously called the baby's name at 10 sec. intervals. When an infant looked at one or the other experimenters, she raised her thumb in camera view. Only crying infants who sucked a sweet pacifier showed a preference for their experimenter. As a group none of the other infants did so. However, there was a wide distribution of sucking times in calm week 6 infants. Choice was linearly related to sucking duration. Infants who sucked for substantial periods of time, showed a strong preference for the experimenter. Those who sucked for minimal periods of time strongly preferred the confederate. Based on these findings and ones from 9- and 12-week-old infants, a model is presented in which preference in this experimental paradigm is determined by idealized levels of central activation. These levels may be inferred from the normal crying function at a particular age.     

Depressed mothers' newborns show longer habituation and fail to show face/voice preference

Twenty neonates of depressed and nondepressed mothers failed to show an initial visual preference for their mother's versus a female stranger's face/voice. Subsequently, infants were habituated to their mother's face and voice. Infants of depressed mothers required 1/3 more trials and almost twice as long to habituate. A posthabituation test with their mother and a different female stranger revealed a preference for the stranger's face for 9 out of the 10 newborns of the nondepressed mothers. Again, the infants of depressed mothers displayed no visual preference. These findings reveal differences in depressed mothers newborns' speed of habituation and face/voice preferences. ©2002 Michigan Association for Infant Mental Health.     

Actors and actions: The role of agent behavior in infants' attribution of goals

Twelve-month-old infants attribute goals to both familiar, human agents and unfamiliar, non-human agents. They also attribute goal-directedness to both familiar actions and unfamiliar ones. Four conditions examined information 12-month-olds use to determine which actions of an unfamiliar agent are goal-directed. Infants who witnessed the agent interact contingently with a human confederate encoded the agent's actions as goal-directed; infants who saw a human confederate model an intentional stance toward the agent without the agent's participation, did not. Infants who witnessed the agent align itself with one of two potential targets before approaching that target encoded the approach as goal-directed; infants who did not observe the self-alignment did not encode the approach as goal-directed. A possible common underpinning of these two seemingly independent sources of information is discussed.     

Fine orientation discrimination and shape constancy in young infants

The present study aimed to investigate simultaneously fine orientation discrimination and shape constancy in young infants. The design employed two variants of the habituation paradigm. Infants in one group were habituated to a single orientation (5 or 15 degrees) of a single stimulus presented repeatedly, and they were then tested with the complementary orientation (15 or 5 degrees). Infants in a second group were habituated to several orientations (5, 10, and 15 degrees) of the same stimulus, and they were then tested with a familiar orientation of the stimulus, with two novel orientations of the same stimulus, and with a new stimulus. Between-groups comparison showed that infants habituated more efficiently to re-presentations of a single orientation than to multiple orientations of the same stimulus, providing evidence of fine orientation discrimination; posthabituation comparison within the single-orientation group confirmed that infants discriminated small orientation changes. Posthabituation comparison within the multiple-orientation group showed that infants generalized over novel orientation changes of the familiar stimulus though they discriminated change to a novel stimulus. Cumulatively, the results of this study demonstrate that under one set of conditions young infants show sensitivity to relatively fine variations in pattern orientation, but that under a different set of conditions young infants give evidence of shape constancy with the same patterns.     

Young infants' generalization of emotional expressions: effects of familiarity

From birth, infants are exposed to a wealth of emotional information in their interactions. Much research has been done to investigate the development of emotion perception, and factors influencing that development. The current study investigates the role of familiarity on 3.5-month-old infants' generalization of emotional expressions. Infants were assigned to one of two habituation sequences: in one sequence, infants were visually habituated to parental expressions of happy or sad. At test, infants viewed either a continuation of the habituation sequence, their mother depicting a novel expression, an unfamiliar female depicting the habituated expression, or an unfamiliar female depicting a novel expression. In the second sequence, a new sample of infants was matched to the infants in the first sequence. These infants viewed the same habituation and test sequences, but the actors were unfamiliar to them. Only those infants who viewed their own mothers and fathers during the habituation sequence increased looking. They dishabituated looking to maternal novel expressions, the unfamiliar female's novel expression, and the unfamiliar female depicting the habituated expression, especially when sad parental expressions were followed by an expression change to happy or to a change in person. Infants are guided in their recognition of emotional expressions by the familiarity of their parents, before generalizing to others.     

Do as I do: 7-month-old infants selectively reproduce others' goals

In the current study, we tested whether 7-month-old infants would selectively imitate the goal-relevant aspects of an observed action. Infants saw an experimenter perform an action on one of two small toys and then were given the opportunity to act on the toys. Infants viewed actions that were either goal-directed or goal-ambiguous, and that represented either completed or uncompleted goals. Infants reproduced the goal of the experimenter only in those cases where the action was goal-directed, in both the complete and incomplete goal conditions. These results provide the first evidence that infants as young as 7 months of age selectively imitate actions based on their goal-directedness, and that they are able to analyze the goals of even uncompleted actions. Even during the first year of life, infants' sensitivity to goal-directed action is expressed not only in their responses in visual habituation procedures, but also in their overt actions.     

Evidence of a shift from featural to configural face processing in infancy

Two experiments examined whether 4-, 6-, and 10-month-old infants process natural looking faces by feature, i.e. processing internal facial features independently of the facial context or holistically by processing the features in conjunction with the facial context. Infants were habituated to two faces and looking time was measured. After habituation they were tested with a habituation face, a switch-face, or a novel face. In the switch-faces, the eyes and mouth of the habituation faces were switched. The results showed that the 4-month-olds processed eyes and mouth by feature, whereas the 10-month-olds processed both features holistically. The 6-month-olds were in a transitional stage where they processed the mouth holistically but the eyes still as a feature. Thus, the results demonstrated a shift from featural to holistic processing in the age range of 4 to 10 months.     

Infant categorization of containment,support and tight‐fit spatial relationships

Two experiments examined infant categorization of containment, support or tight‐fit spatial relationships. English‐learning infants of 10 months (Experiment 1) and 18 months (Experiment 2) were habituated to four pairs of objects in one of these relationships. They were then tested with one event from habituation, one with novel objects in the familiar relationship, one with familiar objects in a novel relationship and one with novel objects in a novel relationship. Infants at both ages generalized their habituation of the containment relationship to novel objects in this relationship. In the support and tight‐fit conditions, the younger infants responded only to the novel objects in the test while the older infants responded to the novel relationship, but only with familiar objects. The results indicate that infants learn to categorize containment prior to support or tight‐fit relationships and suggest that infants can recognize a relationship between familiar objects prior to novel objects.     

Number Versus Contour Length in Infants' Discrimination of Small Visual Sets

This study examined infants' use of contour length in number discrimination tasks. We systematically varied number and contour length in a visual habituation experiment in order to separate these two variables. Sixteen 6- to 8-month-old infants were habituated to displays of either two or three black squares on a page. They were then tested with alternating displays of either a familiar number of squares with a novel contour length or a novel number of squares with a familiar contour length. Infants dishabituated to the display that changed in contour length, but not to the display that changed in number. We conclude that infants base their discriminations on contour length or some other continuous variable that correlates with it, rather than on number.     

Infant sensitivity to audiovisually coherent events

Summary We examined 5-month-old infants' sensitivity to audiovisually coherent and incoherent events. A person speaking and an automobile with engine running were filmed approaching and receding with corresponding (coherent) soundtracks. Infants were tested with a habituation paradigm in which they observed coherent or incoherent films, involving, respectively, acoustical radial motion in the direction seen or opposite to the direction seen. Infants habituated to both person and car films, but coherent events uniformly yielded more rapid habituation than did incoherent ones. In addition, infants treated silent events more like audiovisual coherence than like incoherence. Infants habituated more to cars than to people, suggesting that a speaking person may especially maintain infant attention.     

Infant’s gaze in a teasing task with an experimenter or parent: A naturalistic approach

We assessed infant’s gaze in a teasing task in New York City public spaces. The task was administered to two different groups of 5- to 13-month-old infants. We used a between participants design across two studies. In Study 1 an experimenter administered the task to these infants (n = 79), whereas a parent did so in Study 2 (n = 79). The adult engaged the infant with a toy and then pulled it away to one side by counting to 7. A second trial to the other side was repeated. Infants passed the teasing task if they looked to the adult’s face within the first 5 seconds after removing the toy in at least one trial. In Study 1, we found that infants looked to the experimenter’s face after teasing by 7 months of age. In Study 2, infants did not show any significant gazes to the parent’s face after teasing at any age. Most trained parents successfully administered the teasing task to their infant. A teasing game played by an adult stranger (e.g., experimenter) may be optimal to elicit infant’s gaze in a naturalistic setting. Implications for developing cost-effective social-cognitive milestone measures in non-laboratory settings are discussed.     

Infants' understanding of object-directed action

When and in what ways do infants recognize humans as intentional actors? An important aspect of this larger question concerns when infants recognize specific human actions (e.g. a reach) as object-directed (i.e. as acting toward goal-objects). In two studies using a visual habituation technique, 12-month-old infants were tested to assess their recognition that an adult's reach is directed toward its target object. Infants in the experimental condition were habituated to a display in which an actor reached over a wall-like barrier with an arcing arm movement, to pick up a ball. After habituation infants saw two test displays, for which the barrier was removed. In the direct test event the actor reached directly for the ball, the arm tracing a visually new path, but the action consistent with attempting to reach for the object as directly as possible. In the indirect test event the actor traced the old path, reaching over in an arc, even though the wall was no longer present. This arm movement was identical to that in habituation but no longer displayed a reach going directly to its object. In a control condition infants saw the same movements but in a situation with no goal-object. In the experimental conditions, with a goal object present, infants looked longer at the indirect test event in comparison to the direct test event. In the control conditions infants looked equally at both indirect and direct test events. We conclude that sensitivity to human object-directed action is established by 12-month-olds and compare these results to recent findings by [Gergely, G., Nadasdy, Z., Csibra, G., & Biro S. (1995). Taking the intentional stance at 12 months of age. Cognition, 56, 165-193] and [Woodward, A. (1998). Infants selectively encode the goal object of an actor's reach. Cognition, 69, 1-34].     

Infants' sensitivity to differential luminance as information about depth

To what degree are young infants able to perceive differential shadowing and to what degree are they able to utilize this stimulus parameter as information about depth? Two habituation experiments were performed. In Experiment 1, a group of 5-month-old infants were habituated to a low frequency, vertical, and approximately sinusoidal luminance grating superimposed on a flat colored surface. This display induced stable 3-D perception in adult subjects. After habituation, the infants viewed two test displays at alternating trials. One was made up of real half cylinders matching the light distribution of the habituation display and the other was made up of a square wave grating of the same spatial frequency as in the habituation one. Adults perceived the latter display as flat. Results showed that both test displays were treated as new ones by the infants habituated to the sinusoidal grating. Experiment 2 was identical to Experiment 1, except that the subjects were 3 1/2-month-old. These infants treated the half cylinders as familiar and the square wave grating as new. The results indicate that infants at both age levels (3 1/2 and 5 months of age) were sensitive to the difference between sharp and gradual change in luminance which is a prerequisite for perceiving form from luminance. However, neither age group seemed to utilize gradual change in luminance as information about space.     

Infants' discrimination of happy and sad music

Infants can detect information specifying affect in infant- and adult-directed speech, familiar and unfamiliar facial expressions, and in point-light displays of facial expressions. We examined 3-, 5-, 7-, and 9-month-olds' discrimination of musical excerpts judged by adults and preschoolers as happy and sad. In Experiment 1, using an infant-controlled habituation procedure, 3-, 5-, 7-, and 9-month-olds heard three musical excerpts that were rated as either happy or sad. Following habituation, infants were presented with two new musical excerpts from the other affect group. Nine-month-olds discriminated the musical excerpts rated as affectively different. Five- and seven-month-olds discriminated the happy and sad excerpts when they were habituated to sad excerpts but not when they were habituated to happy excerpts. Three-month-olds showed no evidence of discriminating the sad and happy excerpts. In Experiment 2, 5-, 7-, and 9-month-olds were presented with two new musical excerpts from the same affective group as the habituation excerpts. At no age did infants discriminate these novel, yet affectively similar, musical excerpts. In Experiment 3, we examined 5-, 7-, and 9-month-olds' discrimination of individual excerpts rated as affectively similar. Only the 9-month-olds discriminated the affectively similar individual excerpts. Results are discussed in terms of infants' ability to discriminate affect across a variety of events and its relevance for later social-communicative development.     

Pre-verbal infants perceive emotional facial expressions categorically

Adults perceive emotional expressions categorically, with discrimination being faster and more accurate between expressions from different emotion categories (i.e. blends with two different predominant emotions) than between two stimuli from the same category (i.e. blends with the same predominant emotion). The current study sought to test whether facial expressions of happiness and fear are perceived categorically by pre-verbal infants, using a new stimulus set that was shown to yield categorical perception in adult observers (Experiments 1 and 2). These stimuli were then used with 7-month-old infants (N = 34) using a habituation and visual preference paradigm (Experiment 3). Infants were first habituated to an expression of one emotion, then presented with the same expression paired with a novel expression either from the same emotion category or from a different emotion category. After habituation to fear, infants displayed a novelty preference for pairs of between-category expressions, but not within-category ones, showing categorical perception. However, infants showed no novelty preference when they were habituated to happiness. Our findings provide evidence for categorical perception of emotional expressions in pre-verbal infants, while the asymmetrical effect challenges the notion of a bias towards negative information in this age group.     

Infants’ developing understanding of the link between looker and object

Three studies investigated infants’ understanding that gaze involves a relation between a person and the object of his or her gaze. Infants were habituated to an event in which an actor turned and looked at one of two toys. Then, infants saw test events in which (1) the actor turned to the same side as during habituation to look at a different toy, or (2) the actor turned to the other side to look at the same toy as during habituation. The first of these involved a change in the relation between actor and object. The second involved a new physical motion on the part of the actor but no change in the relation between actor and object. Seven‐ and 9‐month‐old infants did not respond to the change in relation between actor and object, although infants at both ages followed the actor's gaze to the toys. In contrast, 12‐month‐old infants responded to the change in the actor–object relation. Control conditions verified that the paradigm was a sensitive index of the younger infants’ representations of action: 7‐ and 9‐month‐olds responded to a change in the actor–object relation when the actor's gaze was accompanied by a grasp. Taken together, these findings indicate that gaze‐following does not initially go hand in hand with understanding the relation between a person who looks and the object of his or her gaze, and that infants begin to understand this relation between 9 and 12 months.     

The effects of adults' affective expression and direction of visual gaze on 12‐month‐olds' visual preferences for an object following a 5‐minute, 1‐day,or 1‐month delay

Between 12‐ and 14 months of age infants begin to use another's direction of gaze and affective expression in learning about various objects and events. What is not well understood is how long infants' behaviour towards a previously unfamiliar object continues to be influenced following their participation in circumstances of social referencing. In this experiment, we examined infants' sensitivity to an adult's direction of gaze and their visual preference for one of two objects following a 5‐min, 1‐day, or 1‐month delay. Ninety‐six 12‐month‐olds participated. For half of the infants during habituation (i.e., familiarization), the adults' direction of gaze was directed towards an unfamiliar object (look condition). For the remaining half of the infants during habituation, the adults' direction of gaze was directed away from the unfamiliar object (look‐away condition). All infants were habituated to two events. One event consisted of an adult looking towards (look condition) or away from (look‐away condition) an object while facially and vocally conveying a positive affective expression. The second event consisted of the same adult looking towards or away from a different object while conveying a disgusted affective expression. Following the habituation phase and a 5‐min, 1‐day, or 1‐month delay, infants' visual preference was assessed. During the visual preference phase, infants saw the two objects side by side where the adult conveying the affective expression was not visible. Results of the visual preference phase indicate that infants in the look condition showed a significant preference for object previously paired with the positive affect following a 5‐min and 1‐day delay. No significant visual preference was found in the look condition following a 1‐month delay. No significant preferences were found at any retention interval in the look‐away condition. Results are discussed in terms of early learning, social referencing, and early memory.     

Visual habituation in human infants: development and rearing circumstances

Summary Habituation is a type of learning that reflects changing responsiveness to repeated information. In two longitudinal studies, we examined individual differences, stability, and developmental change in the ontogeny of visual habituation in human infants across the middle of the first year of life. To study this phenomenon in breadth, we tested infants from two social classes within the same culture and infants from two different cultures. Infants demonstrated significant, but comparable, individual differences in habituation across socioeconomic and cultural variations in rearing circumstances; they showed significant, if moderate, stability in habituation; and they habituated significantly more quickly with age. These results are interpreted in terms of developing human beings' increasing efficiency in processing visual information near the beginning of extrauterine life.     

Do infants discriminate non-linguistic vocal expressions of positive emotions?

Adults are highly proficient in understanding emotional signals from both facial and vocal cues, including when communicating across cultural boundaries. However, the developmental origin of this ability is poorly understood, and in particular, little is known about the ontogeny of differentiation of signals with the same valence. The studies reported here employed a habituation paradigm to test whether preverbal infants discriminate between non-linguistic vocal expressions of relief and triumph. Infants as young as 6 months who had habituated to relief or triumph showed significant discrimination of relief and triumph tokens at test (i.e. greater recovery to the unhabituated stimulus type), when exposed to tokens from a single individual (Study 1). Infants habituated to expressions from multiple individuals showed less consistent discrimination in that consistent discrimination was only found when infants were habituated to relief tokens (Study 2). Further, infants tested with tokens from individuals from different cultures showed dishabituation only when habituated to relief tokens and only at 10–12 months (Study 3). These findings suggest that discrimination between positive emotional expressions develops early and is modulated by learning. Further, infants' categorical representations of emotional expressions, like those of speech sounds, are influenced by speaker-specific information.     

Influence of vocal cues on learning about objects in joint attention contexts

An experimenter taught infants about a novel toy in two joint attention conditions, one with and one without vocal cues. In test trials, infants viewed the familiar toy and a novel toy. Infants in the Joint Attention plus Voice condition looked significantly longer to the novel toy.