Infant psychology focuses on the earliest stages of human development, from conception to the age of 2 years old approximately, which are characterized by rapid growth and lasting consequences on physical and mental health. During this period infants develop neurologically and that shapes their emotions, responses to life situations, future relationships, mature personality, mood and learning abilities. Psychologists explore the main components of human development such as cognitive growth, motor development, language abilities, social and emotional capacities. Environmental, social and attachment experiences during infancy significantly affect the person's later stages of development. Neglect, abuse or traumatic experiences during early age shape the child as a person because this period is viewed by psychologists as the most important phase of human development.
Primitive automotive movements known as reflexes are innate and they develop early in the uterus, however, motor development as a whole depends on brain formation after birth. Those reflexes help the fetus leave the womb during delivery and are a basis for future learned behaviors like standing and walking. Some examples would be the crawl, standing and step reflexes as well as the Moro reflex which makes the infant stretch out its arms and legs to reach out for objects and people.
The first stage of cognitive development, the sensori-motor stage, is when infants learn to coordinate their automotive movements with sensory activity. Jean Piaget (1896 to 1980) put forward a theory of cognitive development which describes the development of human intelligence and the infant's capacities for reasoning and understanding. In order to adapt to their environment, children learn to grasp information and use it through the processes of assimilation and accommodation. According to Piaget the assimilation process enables the infant to acquire new facts about the world and adapt it to the already acquired information so that they can make sense of it. Accommodation, on the other hand, is the process of altering the acquired information and forming new concepts and frameworks. Research shows that children actively use sensory stimuli to develop their mental activity.
From the five human senses the one that is the most developed in newborns is touch; the least developed is sight. At first the infant discovers and interacts with the surrounding environment through smell, sound and touch. Newborns' hearing is developed to an extent that they can recognize their parents' voice, though they seem to prefer the mother's voice. The sense of smell is also highly developed at birth so that babies can recognize the odor of the mother's breast pads and that of other important people in their lives. The sense of touch is the most important of all senses because it serves as a means of communication between the infant and the mother, and deepens the feeling of attachment. Mothers respond to the infant's needs by holding, cuddling or patting them which creates in them a sense of security and comfort. According to John Bowlby, the father of attachment theory, this is how the infant and the mother interact and reactions like crying, grasping, suckling or smiling represent the child's need for his mother and show the level of attachment to her.
If the mother is unresponsive to the needs of the child and neglects it, the infant realizes how helpless and powerless it is without the cares of another individual. Such stress also has lasting effects on the infant's mental health because it is directly connected with its survival and safety. One of the most stressful experiences for every infant is the separation from the mother which visibly increases the levels of cortisol, known as "the stress hormone," in the child. Research shows that high levels of cortisol in infants lead to emotional problems later in life such as depression, anxiety and suicidal tendencies, or in other cases result in alcoholism or eating disorders.
If the early relationships are strong and secure, the individual will develop both his psychological and physiological capacities. Therefore, the infant learns how to control his emotions and look for help when needed as a result of his mother's reliability and responsiveness to his early needs. Emotionally deprived individuals usually have low self-esteem and lack confidence and that seriously affects their social development and diminishes their capacity to deal with life's challenges.