The Size Distance Invariance Hypothesis and Binocular Size Perception

DOI: 10.5176/2251-1865_CBP15.34

Authors: Nam-Gyoon Kim

Abstract:

For too long, size perception research has been guided by the size distance invariance hypothesis (SDIH). Although research to validate this hypothesis has been largely inconclusive, the hypothesis has endured, perhaps in part because alternative information sources for size perception were lacking. Here, I present the results of an experiment in which participants viewed a virtual object stereoscopically then judged its size and distance. Importantly, the experiment explicitly manipulated participants’ interpupillary distance (IPD). Results showed that size and distance judgments were overestimated under a diminished IPD, but underestimated under an enlarged IPD. Significantly, size and distance judgments were affected differently by IPD manipulation, demonstrating that size and distance are independent, rather than interdependent percepts as the SDIH assumes.

Keywords: binocular size perception, distance perception, size distance invariance hypothesis interpupillary distance