Emergence of drawing devices for total and partial occlusion: a longitudinal study

The developmental emergence of two drawing devices was investigated in young children: the use of omission (ie not drawing any of a hidden object) to depict total occlusion and the use of hidden line elimination (HLE, ie deleting only that part of an object that is hidden from view) to depict partial occlusion in a three-dimensional scene. Three groups of school children (5, 6, and 7 years old) were tested individually with two tasks four times over a 2-year period. One task called for the omission device (to draw a cup with its handle not in view) and the other for the HLE device (to draw one ball behind and partially occluded by another). The stimuli in each task were presented in pairs, with one member of the pair showing the occluded scene and the other a canonical or not-occluded scene. Changes in the strategies used by the children to indicate the visual differences within the pairs were recorded over the four testing sessions. Children were found to use the omission device more readily with the cup task than the HLE device with the ball task. There was an age-related trend in every task in the use of the drawing device appropriate to that task. For those who did not use the drawing device appropriate for a perspective drawing, there was a tendency for each age group to favour a particular strategy for representation. The advantage of using a longitudinal design to chart the developmental trend of the emergence of these two drawing devices is discussed.