Infancy

Emotions pervade infants' daily lives in that they are the means by which infants accomplish their goals, as well as the primary medium through which communication occurs. Newborns display general patterns of distress and excitement. Later in the first year, other emotional expressions develop such as joy, surprise, sadness, disgust, anger, and fear. For example, infants begin to smile at others around six to eight weeks of age and begin to show wariness of strangers, as well as separation distress, between seven to nine months of age. More complex emotions, including embarrassment, pride, shame, and guilt, become evident in the last half of the second year.

Emotional expressions are displayed not only by the infant but also by the caregiver. Developmentalists have found that infants begin to detect adults' emotional displays (vocal and facial) by the age of two months. For example, young infants are able to distinguish between a smiling face and one that appears to be frowning. It is not until the middle of the first year that infants begin to understand the meaning of facial displays (i.e., understanding that the displays are emotional). Beginning around ten months of age, infants use the emotional displays of others to regulate their own behavior toward events they encounter in the world, a phenomenon called social referencing. For example, infants at the end of the first year will avoid ambiguous objects toward which their caregivers act disgusted, while they will approach and touch objects toward which their caregivers smile.

Individual differences in infants' socioemotional development have fascinated developmentalists for decades, particularly infants' attachment styles and temperamental differences. Attachment refers to an enduring emotional tie that one person forms to another. It is a tie in which the infant takes another (typically the caregiver) as a protective figure, finding increased security in their presence, missing them in their absence, seeking them in times of stress or alarm, and using them as a secure base from which to explore. According to John Bowlby, the tendency for infants to form attachments is evolutionarily based, being evident across cultures and in other mammalian species. All human infants, even those who have been mistreated and abused, form attachments to others.

The attachment behaviors that infants display change with development. The very young infant can only cry when distressed, look to the caregiver if he or she is nearby, and be attractive to adults. In time, however, infants take on an increasingly active role. Older infants can deliberately signal to the attachment figure by, perhaps, calling for the caregiver. Furthermore, infants acquire the ability to remain in close proximity to their attachment figure with the onset of crawling between seven and nine months.

While all infants form attachments, there are individual differences in infants' attachments that have enduring socioemotional consequences. Mary Ains-worth devised a laboratory procedure (called "strange situation") consisting of a series of maternal separations and reunions designed to categorize twelve-month-old infants' attachment styles to their caregivers. According to this research, infants can be categorized into three groups depending on the attachment behaviors they display: (1) "securely attached" infants seek comfort from the caregiver during reunions and, once comforted, play with toys; (2) "insecurely attached-avoidant" infants avoid their mothers during reunion and focus their attention on their play; and (3) "insecurely attached-resistant" infants are ambivalent during reunion, first approaching the caregiver and then pushing her away. Through subsequent research a fourth category of infants was identified in which infants in the Strange Situation display "disorganized-disorganizing" attachment behavior, characterized by contradictory behavior toward their mothers during reunion (e.g., walking to the mother and then abruptly falling to the floor and rocking).

Attachment researchers have found a consistent relation between infants' attachment behaviors in the Strange Situation and infants' history of interaction with their primary caregivers. Mothers of "securely" attached infants tend to be sensitive and responsive to their infants' emotional signals, whereas mothers of "insecure" infants tend to ignore or to respond inconsistently to their infants' emotional signals. Infants who are classified as "disorganized-disoriented" tend to have caregivers who are frightening to, or frightened of, their infants. In sum, infants' history of interaction influences their quality of attachment, which, in turn, is related to their socioemotional development later in life.

In contrast to the individual differences in attachment thought to arise because of varying interactional histories, temperament researchers study enduring differences in emotionality, and behavioral responses to stimuli, that are due to constitutional factors. Various researchers have identified various temperamental attributes, but most researchers agree that the following are important components of temperament:

• Activity level—the typical pace or vigor of one's activities
• Irritability/negative emotionality—how easily or intensely upset one becomes over negative events
• Soothability—the ease with which one calms after becoming upset
• Fearfulness—one's wariness of intense or highly unusual stimulation
• Sociability—one's receptiveness to social stimulation

Behavioral genetic studies comparing identical twins to fraternal twins indicate that the components of temperament are moderately heritable. In addition, infants' temperament, particularly activity level, irritability, sociability, and shyness, endures to some extent into childhood and adulthood. One important point, however, is that temperament does not determine personality in later life. The study of temperament thus highlights a significant principle that cuts across all developmental phenomena; biology dynamically interacts with environment in the development of humans.

When taken together, some of the key findings in infants' physical, perceptual, motor, cognitive, and socioemotional development indicate that infants are qualitatively different from adults; infants are not simply miniature adults. Furthermore, development is characterized by several reorganizations both within and between domains, thereby precipitating changes in infants' perceptions of the world, as well as the way in which they act upon it. The period of infancy is likely to continue to generate fundamental and important questions that challenge scientists.