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This is my psychology homework.
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Piaget’s theory postulates that there are four major stages in cognitive development. The preoperational stage is the second stage that period from about two to seven years of age. In this period, they are learning language and start to use symbolic thought and memory skills. However they have not yet developed the conservation and reversibility. The conservation is the principle that properties such as mass, volume, and number remain the same despite changes in the forms of objects. (Textbook page:150) They are also egocentric; their view of the world is very self-centered.

During the weekend I visited my friend’s house. He has a three years and two months old girl named Jina. Before dinner served, I conducted one of Piaget’s conservation experiments. I picked out two identical clear glasses and filled with the same amount of water. Then I asked her, “Jina, do you see those two cups with water in it? Which cup has more water in it, or are they have same amount of water?” She said they have same amount of water in two glasses. After she answered my question, I brought a more narrow and tall glass. Then I poured all the water from one of two cups that I just saw it to her I asked her again. “Jina, which cup has more water in it, or are they have same amount of water?” she said the narrow and tall cup has more water in it than other cup even though they have the same amount.

Jina was not able to conserve because lack of conservation and reversibility. She focused only one dimension. She noticed change in level of water but did not notice that other aspects of the situation have changed simultaneously.