1a) The sensorimotor stage occurs when an infant is just born and lasts until their second year of life. During this stage of cognitive development, children get knowledge and learn about the world through sensory experience such as sucking, looking, listening, biting, etc. 1b) «Object permanence» is the term used to describe a child’s ability to understand and realize that certain objects continue to exist even after you can no longer see them. Piaget would explain the absence of object permanence in young infants with the reason of the weak memory that the children have which prevent them from learning the object permanence at such an early age. According to Piaget, object permanence starts developing around the period of 8 months as an infant’s memory improves and begin to functionalize better. 1c) After the object permanence’s development children soon tend to experience stranger anxiety which is a specific fear of people that they are unfamiliar with. According to Piaget, stranger anxiety starts developing around the same age as the object permanence does – 8 months. However, object permanence and stranger anxiety can emerge at the same time because children are able remember and build schemas for the new things or people. 1d) McCrink and Wynn outline the theory of cognitive competency that differs from Piaget’s one. McCrink and Wynn suppose that infants can understand numerosity and perform the basic mathematical operations with numbers such as addition and substruction. Before their theory was examined, everyone thought that infants used object tracking processes to help with addition and substruction which only works with small numbers.