Fundamental measurement of perceived length and perceived area

Using the method of counting mental units the study explored whether judged lengths and area in right triangles, squares, and disks were consistent with the geometric relationships in these surfaces. Judgments were found to consist with these relationships supporting the idea that they were fundamental measures of perceived extents. Fundamental measures obtained by mental counting differ from corresponding measures obtained by magnitude estimation, rating, and nonmetric scaling. Reasons are suggested as to why these other methods may be biased.