Children's Perception of Proportion in Graphs

Children ranging in age from 9 to 13 years made judgments of proportion with a variety of graphical elements in 2 experiments. Younger children can be misled by irrelevant dimensions of objects used to portray magnitudes and proportions, but older children make their judgments like adults, ignoring or accommodating the extra dimensions. Although the psychophysical function for older children and adults is approximately linear, closer inspection reveals a complex pattern of bias that is not captured by traditional psychophysical models. A characteristic pattern of over- and underestimation was observed and also turns out to be present, but previously unnoticed, in judgments made by adults. The pattern of bias is consistent with the view that the visual system extracts real or virtual axes of symmetry and that subjects use these, in addition to the object boundaries, as points of reference when making their judgments. A model that assumes repulsion of judgments away from these reference points is described and fitted to the children's data. The model is motivated by both neurophysiological and cognitive considerations.