Visual size invariance does not apply to geometric angle and speed of rotation

The ability of humans to visually estimate geometric angle and speed of rotation was examined as a function of the spatial scale of the stimuli. Both properties are objectively invariant at different spatial scales, but the results of experiments show that the judgement of acute geometric angles as well as that of speed of rotation varies strongly and monotonically with the scale of presentation. If the image is magnified, the perceived geometric angle and the perceived speed of rotation increase. If the image is reduced in size, they decrease. This result imposes strong constraints on perceptual theories.