Glennerster A, Rogers B J, Bradshaw M F
Department of Experimental Psychology, University of Oxford, UK.
Perception. 1998;27(11):1357-65. doi: 10.1068/p271357.
A veridical estimate of viewing distance is required in order to determine the metric structure of objects from binocular stereopsis. One example of a judgment of metric structure, which we used in our experiment, is the apparently circular cylinder task (E B Johnston, 1991 Vision Research 31 1351-1360). Most studies report underconstancy in this task when the stimulus is defined purely by binocular disparities. We examined the effect of two factors on performance: (i) the richness of the cues to viewing distance (using either a naturalistic setting with many cues to viewing distance or a condition in which the room and the monitors were obscured from view), and (ii) the range of stimulus disparities (cylinder depths) presented during an experimental run. We tested both experienced subjects (who had performed the task many times before under full-cue conditions) and naïve subjects. Depth constancy was reduced for the naïve subjects (from 62% to 46%) when the position of the monitors was obscured. Under similar conditions, the experienced subjects showed no reduction in constancy. In a second experiment, using a forced-choice method of constant stimuli, we found that depth constancy was reduced from 64% to 23% in naïve subjects and from 77% to 55% in experienced subjects when the same set of images was presented at all viewing distances rather than using a set of stimulus disparities proportional to the correct setting. One possible explanation of these results is that, under reduced-cue conditions, the range of disparities presented is used by the visual system as a cue to viewing distance.
为了从双眼视差中确定物体的度量结构，需要对视距进行准确估计。我们在实验中使用的一种度量结构判断示例是视圆柱任务（E B 约翰斯顿，1991年《视觉研究》31卷 1351 - 1360页）。大多数研究报告称，当刺激仅由双眼视差定义时，在该任务中存在恒常性不足的情况。我们研究了两个因素对表现的影响：（i）视距线索的丰富程度（使用具有许多视距线索的自然场景或遮挡房间和显示器使其不可见的条件），以及（ii）实验过程中呈现的刺激视差范围（圆柱深度）。我们测试了有经验的受试者（他们之前在全线索条件下多次执行该任务）和新手受试者。当显示器位置被遮挡时，新手受试者的深度恒常性降低（从62%降至46%）。在类似条件下，有经验的受试者的恒常性没有降低。在第二个实验中，使用恒定刺激的强制选择方法，我们发现当在所有视距呈现同一组图像而不是使用与正确设置成比例的一组刺激视差时，新手受试者的深度恒常性从64%降至23%，有经验的受试者从77%降至55%。这些结果的一种可能解释是，在线索减少的条件下，视觉系统将呈现的视差范围用作视距线索。
