Li et al (1999)
Piaget and Inhelder's (1956) study of conservation is a classic in developmental psychology. Part of their research required children to correctly predict the water surface orientation in half-filled bottles that were tilted. As you can see in the images below, the tilting of the bottle always results in a horizontal line. Piaget and Inhelder would argue that this was part of a child's cognitive maturation and that...