Abstract
Introduction The phenomenon of size-distance paradox has been poorly understood in terms of its factors. We investigated this issue with an optical tunnel, an apparatus for systematically controlling nested angular extents for size and distance perceptions. Manipulations in the tunnel were expected to differentially affect perceived size (S') and perceived distance (D') as suggested by the paradox. While size contrast and depth cues were controlled for, effects of optical tunnel's structural relations on S' and D' were examined. Method 28 participants were divided into two groups across which the density of the optical tunnel was manipulated: dense versus sparse. For any of the two, one of four differently sized 2-D discs stuck on the center of a white sheet was placed in the middle of the tunnel at one of four locations. Participants viewed it monocularly, and reproduced its size and distance by adjusting a size meter and a distance meter respectively. Results Both S' and D' were underestimated in the tunnel but with different trends. D' was underestimated more at further locations for both groups, F(3,78)=442.34, p< 0.001. S', however, was underestimated less at further locations for the sparse group, F(3,39)=3.32, p=0.030; that is, S' increased with increasing underestimation of D'. Further, S' showed a quadratic trend for the dense group, F(3,39)=12.30, p< 0.001; specifically, S' increased and then decreased with increasing underestimation of D'. Discussion/Conclusion The effect of location on S' and D' showed a size-distance paradox for both dense and sparse optical tunnel conditions in slightly different ways. Given that size contrast and depth cues were controlled for in each tunnel condition, the paradoxical effect may be attributable to the optical tunnel's structural variable, possibly the ratio of the frontal surface area embedding the stimulus disc to the length and density of the visible longitudinal tunnel structure.
Meeting abstract presented at VSS 2016