From SNARC to SQUARC: Universal Mental Quantity Line?

Numbers are represented spatially. Evidence for this comes from the SNARC effect (Spatial-Numerical Association of Response Codes). Small numerals are accessed faster on the left and large ones on the right. The effect assumes a mental number line. However, in A Theory of Magnitude (ATOM), both numerical (discrete) and non-numerical (continuous) quantities share a common processing mechanism. Thus, the SNARC effect may be an instance of a general SQUARC effect (Spatial-Quantity Association of Response Codes). We devised two experiments to test this hypothesis. First, 85 Japanese students bisected a quantity of water. They showed bisection bias by overestimating the right cup and underestimating the left one. In the second experiment, small continuous magnitudes shifted covert visual attention leftward, with larger ones shifting it rightward. Our data suggest that SNARC may be part of SQUARC, and the mental number line may be in fact a mental quantity line.