Ooi Teng Leng, Wu Bing, He Zijiang J
Department of Basic Sciences, Pennsylvania College of Optometry, 8360 Old York Road, Elkins Park, PA 19027, USA.
Perception. 2006;35(5):605-24. doi: 10.1068/p5492.
Correct judgment of egocentric/absolute distance in the intermediate distance range requires both the angular declination below the horizon and ground-surface information being represented accurately. This requirement can be met in the light environment but not in the dark, where the ground surface is invisible and hence cannot be represented accurately. We previously showed that a target in the dark is judged at the intersection of the projection line from the eye to the target that defines the angular declination below the horizon and an implicit surface. The implicit surface can be approximated as a slant surface with its far end slanted toward the frontoparallel plane. We hypothesize that the implicit slant surface reflects the intrinsic bias of the visual system and helps to define the perceptual space. Accordingly, we conducted two experiments in the dark to further elucidate the characteristics of the implicit slant surface. In the first experiment we measured the egocentric location of a dimly lit target on, or above, the ground, using the blind-walking-gesturing paradigm. Our results reveal that the judged target locations could be fitted by a line (surface), which indicates an intrinsic bias with a geographical slant of about 12.4 degrees. In the second experiment, with an exocentric/relative-distance task, we measured the judged ratio of aspect ratio of a fluorescent L-shaped target. Using trigonometric analysis, we found that the judged ratio of aspect ratio can be accounted for by assuming that the L-shaped target was perceived on an implicit slant surface with an average geographical slant of 14.4 degrees. That the data from the two experiments with different tasks can be fitted by implicit slant surfaces suggests that the intrinsic bias has a role in determining perceived space in the dark. The possible contribution of the intrinsic bias to representing the ground surface and its impact on space perception in the light environment are also discussed.
在中等距离范围内正确判断自我中心/绝对距离，需要准确呈现地平线以下的角度偏斜和地面信息。这一要求在明亮环境中可以满足，但在黑暗中则无法满足，因为在黑暗中地面不可见，因此无法准确呈现。我们之前表明，黑暗中的目标是在从眼睛到目标的投影线与一个隐式表面的交点处被判断的，该投影线定义了地平线以下的角度偏斜。隐式表面可以近似为一个倾斜表面，其远端朝着正平行平面倾斜。我们假设隐式倾斜表面反映了视觉系统的内在偏差，并有助于定义感知空间。因此，我们在黑暗中进行了两项实验，以进一步阐明隐式倾斜表面的特征。在第一个实验中，我们使用盲人行走手势范式测量了地面上或地面上方昏暗照明目标的自我中心位置。我们的结果表明，判断出的目标位置可以用一条线（表面）拟合，这表明存在约12.4度地理倾斜的内在偏差。在第二个实验中，通过一个外中心/相对距离任务，我们测量了荧光L形目标的判断长宽比。使用三角分析，我们发现判断出的长宽比可以通过假设L形目标是在平均地理倾斜为14.4度的隐式倾斜表面上被感知来解释。来自两项不同任务实验的数据都可以用隐式倾斜表面拟合，这表明内在偏差在黑暗中确定感知空间方面发挥了作用。我们还讨论了内在偏差对呈现地面的可能贡献及其在明亮环境中对空间感知的影响。
