Size constancy in Virtual Reality

Size constancy enables us to have a stable size representation of an object despite changing retinal angular size at different viewing distances. However, it is unknown whether size constancy is maintained in virtual reality (VR), in which ample depth cues are available as in the real world. In the present study, we aimed to test size constancy in VR by assessing whether the size estimation of an object is affected by viewing distance. In our experiment, naïve observers (n=22) viewed a standard sphere (diameter of 40 cm) at 2 m and a test sphere at various viewing distances (2-12 m) simultaneously. They adjusted the size of the test sphere presented with a random diameter so that it looked equal to the physical size of the standard sphere. The results showed that at a near distance (~8 m), size constancy was preserved: the estimated size of the test sphere was not different from the size of the standard sphere. However, size constancy was progressively impaired as the distance increased above 8 m and our observers’ PSEs were systematically reduced (10 m: 36.28 cm, p = 0.012, 12 m: 33.23 cm, p < 0.001), which means that they overestimated the size of the test sphere. Our finding suggests that size constancy in VR might be affected by the well-known underestimation of distance in VR.