Distance perception for points at equiconvergence and equidistance loci

Subjects viewed luminescent targets placed at an equidistance (ED) locus or on a comparable equiconvergence locus, the Vieth-Müller circle (VMC). In darkness, subjects moved the index finger to the apparent distance of the visible target. This was repeated at leftward eccentricities of 0 degrees (straight ahead), 15 degrees, 22.5 degrees, 30 degrees, 37.5 degrees, and 45 degrees. Contrary to theoretical expectations, apparent distance to points on the VMC did not describe an equidistance locus, but diminished significantly with increasing eccentricity, whereas ED settings increased slightly but significantly. Binocular and monocular groups performed equivalently. Veridicality of results appears to be the outcome of an accommodation-convergence conflict with a dominant role for accommodation.