Is this a real 3D shape? An investigation of construct validity and item difficulty in the PSVT:R

The Purdue Test of Spatial Visualization (PSVT:R) is a widely used measure of spatial ability. Though the PSVT:R is considered to be a mental rotation test, degree of angular disparity between shapes does not correspond with degree of item difficulty. In the present study, we investigate the possibility that drawings that do not naturally look like 3D shapes could affect item difficulty in the Revised PSVT:R. We conducted a shape sorting task in which participants (N = 588) were asked whether shapes from the Revised PSVT:R looked like real 3D solid shapes or not. We also made a modified version of the Revised PSVT:R in which we changed which answer was correct and compared with performance on the Revised PSVT:R (N = 807). Some questions that should have been easier based on the degree of rotation instead became harder. Our results suggest that some of the isometric drawings in the PSVT:R may not clearly look like 3D shapes and that this fact may explain why item difficulty does not correspond to degree of rotation. Our findings raise questions about whether the PSVT:R can be considered to measure mental rotation as traditionally understood.