Viewing an object from above: The role of height in the visual field and object contour in the perception of 3-D shape

In many instances, 3-D shape from binocular disparity is systematically misperceived, consistent with the overestimation of near distances and the underestimation of far distances (Johnston, 1991 Vision Research 31 1351 - 1360). Generally, the experimental stimuli in these situations have been presented at eye height, but in most natural tasks where binocular vision may be important, such as prehension, objects are viewed from above. This provides improved information in the form of (i) additional distance information from height in the visual field (Watt and Bradshaw, 2002 Spatial Vision 15 253 - 254), and (ii) a view of the upper surface of the object and contour, which provides a disparity discontinuity across the edge of the object, that may be particularly useful in judging 3-D object shape. Here, we investigated the contribution of these cues in a standard apparently circular cylinder task. A view of the upper surface of the object and contour improved disparity scaling compared to when the only additional cue was height in the visual field; this, together with other research, suggests that the visual system uses both sources of information when scaling disparity.