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2. Principles of mental imagery;Finke,1989
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4. The role of the meaning in the urban image;Harrison;Environment and Behavior,1972
5. Huitt, W., & Hummel, J (2003) Piaget's theory of cognitive development. Educational Psychology Interactive. Valdosta, GA: Valdosta State University. Retrieved [28 September 2010] from http://www. edpsycinteractive. org/topics/cogsys/piaget. html.