Babies are not only growing physically during the first 2 years of life, but also cognitively (mentally). Every day while they interact with and learn about their environment they are creating new connections and pathways between nerve cells both within their brains, and between their brains and bodies. While physical growth and change is easily observed and measured in precise terms such as in inches and pounds, cognitive change and development is a little harder to determine as clearly. Therefore, much about what experts know about mental and cognitive development is based on the careful observation of developmental theorists and their theories, such as Piaget's theory of cognitive development and Erickson's psychosocial stages. Bronfenbrenner's ecological model also helps explain infant mental growth to some extent.
According to Piaget, newborns interact with their environment entirely through reflexive behaviors. They do not think about what they're going to do, but rather follow their instincts and involuntary reactions to get what they need: food, air, and attention. Piaget believed that as babies begin to grow and learn about their environment through their senses, they begin to engage in intentional, goal-directed behaviors. In other words, they begin to think about what they want to accomplish, how to accomplish it, and then they do it. This is also when infants develop object permanence, which is the ability to understand that something still exists even if it can't be seen. These two milestones, goal-directed behavior and object permanence, are the highlights and major accomplishments of infant cognitive development.
Piaget separated infancy into six sub-stages, which have been adjusted somewhat over the years as new research and discoveries have occurred The sub-stages include: reflexive activity, primary circular reactions, secondary circular reactions, coordination of secondary schemes, tertiary circular reactions, and beginning or representational thought. While these sub-stages sound highly confusing and complicated, they will be explained in more detail in the next paragraphs in order to simplify them and highlight the important aspects of each.
The first sub-stage is reflexive activity, which lasts from birth to approximately 1 month. According to Piaget, while babies are engaging in reflexive actions such as sucking when offered a bottle or the breast, or other reflexes covered earlier in this article, they are learning about their environment and how they can interact with it. Babies don't think about behaving reflexively; they simply act out those reflexes automatically.
The second sub-stage is primary circular reactions, which spans the ages of 1 to 4 months. During this time, babies intentionally repeat actions that bring them pleasure and desired outcomes. In other words, they do things on purpose because it feels good or it gets them what they want. For example, a small infant may suck on her fist because it feels good to her and it soothes her. Researchers believe that babies of this age may also develop expectancy about cause and effect situations. Babies will begin to see that a pattern of events is connected, and begin to expect the second event after they experience the first event. For example, a baby of this age may learn that when they see a bottle, they expect they will soon be fed. Babies' expectancies about the predictability of their environment form the foundation of Erickson's observation that young infants learn to either trust or mistrust their environment. If a baby learns the pattern that they have a need, such as hunger or discomfort, and that need is regularly addressed, they learn to expect their needs to be met and they learn to trust. On the other hand, if babies learn a pattern that they have needs and those needs are not regularly addressed, they will learn to expect that their needs will not be met and they learn to mistrust the world around them.