Visual and Haptic Size Perception of Stimulus Length, Area, and Volume

Visual and haptic size perception of length (1D), area (2D), and volume (3D) was investigated with the magnitude estimation method. In the visual condition, subjects viewed lines, outlined circles or shaded spheres presented on LCD monitor, and assigned numbers to the perceived length, area or volume of the stimuli. In the haptic condition, subjects grasped rectilinear, cylindrical or spherical blocks which were occluded from subjects' view and assigned numbers. For both conditions, the data were well described by power functions of length, area or volume of the stimuli, and exponents of the power functions became smaller with increasing dimensionality. For the visual (but not haptic) condition, when the data were described by power functions of length (for 1D) or diameter (for 2D and 3D), exponents were approximately constant at around1.0. This suggests that the determinant of the visual size perception for 2D and 3D stimuli may be length rather than area or volume. The critical role of 1D cue for the visual size perception may cause elongation bias, as termed by Holmberg (1975).