The correct answer is: Humans are the only ones who experience this period.
The critical period of development is an important time of development in humans and animals. During this period of development both humans and animals are learning different and crucial abilities, emotions, life skills, coping mechanisms and so forth in order to grow and develop for means of survival essentially. This period is when we are all sensitive to what is going on around us in our environment. Parents need to be aware of what they are subjecting their infants too as what we learn from that age molds and shapes us in a very large way into who we become as adults.