Evidence for good recovery of lengths of real objects seen with natural stereo viewing

Six experiments are described in which good performance of the task of matching the lengths of two stationary real objects, gnarled wooden sticks, under a variety of binocular viewing conditions, including variations in viewing distances was demonstrated. Relatively poor matching performance was observed when the sticks were viewed monocularly in oscillatory motion, or monocularly and stationary. The results suggest that stereo can support good representations of metric scene structure when length judgments of natural objects are required under (quasi-)natural viewing. The implications of these results for theories of structure from stereo and structure from motion are discussed.