Size Constancy and Angular Size Matching in Size Perception of Near Objects

Accurate judgment of the relative sizes of near objects at various distances is important for a variety of occupational visual tasks. This study involved matching the apparent size of each of a series of standard targets, placed at distances between 0.2 and 3 m and all subtending 2 degrees at the eye, with a comparison target of similar geometry, but at a fixed distance of 2 m. Natural binocular viewing of the targets demanded exercise of accommodation and convergence in an environment rich in cues to target size and distance. As the available cues were reduced, judgements of the lateral dimensions of the targets were found to change gradually from those predominantly based on size constancy to those mainly based on angular size matching. These results are qualitatively very similar to those observed in past studies with more distant objects and emphasize the need to maintain adequate cues if linear size is to be judged accurately.