Element density and the efficiency of binocular matching

Constraints on binocular matching were investigated by comparing the thresholds for interocular correlation in random element displays for human and model observers, with element density manipulated as a parameter. The models consisted of ideal decision rules operating on the entire stimulus, only on the edges in the stimulus, or only on the sparse minority elements in the stimulus. The results indicate that the human visual system selectively attends to the stimulus edges or to the sparse elements under most circumstances. Efficiencies (human or model) were highest at very low element densities (approximately 20%) and decreased with increasing element density with a log-log slope of -0.5, indicating that dynamic random element stereograms at the traditional 50% element density are vastly undersampled.