The relationship between the height dimension and numerical processing.

It is well documented that the ability to perceive numbers depends on perception of size. However, size consists of two different dimensions: height and width. In previous size-congruency experiments, the changes in the size dimension were confounded by changes in both the height and width dimensions. Hence, it is not clear if two digits that are equal in size but with different width and height produce a congruency effect and if so, which dimension (height or width) will be associated with quantity more prominently. In fact, different theories might predict different outcomes for the association of height versus width with numbers. To resolve this issue, this study included two experiments in which two equal-size digits that differed from each other in the height and width dimensions were presented and participants were asked to decide which digit is numerically larger. The results revealed a novel congruency effect in which larger numbers are associated more prominently with the height dimension when compared with the width dimension. This effect has important implications for understanding the relationship between number processing and the spatial perception system.