Chen Chien-Chung, Tyler Christopher William
Department of Psychology, National Taiwan University, Taipei, Taiwan; Center for Neurobiology and Cognitive Science, National Taiwan University, Taipei, Taiwan.
Smith-Kettlewell Eye Research Institute, San Francisco, California, United States of America; Division of Optometry and Visual Science, School of Health Sciences, City University, London, United Kingdom.
PLoS One. 2015 Aug 10;10(8):e0132658. doi: 10.1371/journal.pone.0132658. eCollection 2015.
Perceived depth is conveyed by multiple cues, including binocular disparity and luminance shading. Depth perception from luminance shading information depends on the perceptual assumption for the incident light, which has been shown to default to a diffuse illumination assumption. We focus on the case of sinusoidally corrugated surfaces to ask how shading and disparity cues combine defined by the joint luminance gradients and intrinsic disparity modulation that would occur in viewing the physical corrugation of a uniform surface under diffuse illumination. Such surfaces were simulated with a sinusoidal luminance modulation (0.26 or 1.8 cy/deg, contrast 20%-80%) modulated either in-phase or in opposite phase with a sinusoidal disparity of the same corrugation frequency, with disparity amplitudes ranging from 0'-20'. The observers' task was to adjust the binocular disparity of a comparison random-dot stereogram surface to match the perceived depth of the joint luminance/disparity-modulated corrugation target. Regardless of target spatial frequency, the perceived target depth increased with the luminance contrast and depended on luminance phase but was largely unaffected by the luminance disparity modulation. These results validate the idea that human observers can use the diffuse illumination assumption to perceive depth from luminance gradients alone without making an assumption of light direction. For depth judgments with combined cues, the observers gave much greater weighting to the luminance shading than to the disparity modulation of the targets. The results were not well-fit by a Bayesian cue-combination model weighted in proportion to the variance of the measurements for each cue in isolation. Instead, they suggest that the visual system uses disjunctive mechanisms to process these two types of information rather than combining them according to their likelihood ratios.
感知深度由多种线索传达，包括双眼视差和亮度阴影。基于亮度阴影信息的深度感知取决于对入射光的感知假设，研究表明该假设默认采用漫射照明假设。我们聚焦于正弦波纹表面的情况，以探讨在漫射照明下观察均匀表面的物理波纹时，由联合亮度梯度和固有视差调制所定义的阴影和视差线索如何结合。通过正弦亮度调制（0.26或1.8周/度，对比度20%-80%）模拟此类表面，该调制与相同波纹频率的正弦视差同相或反相调制，视差幅度范围为0'-20'。观察者的任务是调整比较随机点立体图表面的双眼视差，以匹配联合亮度/视差调制的波纹目标的感知深度。无论目标空间频率如何，感知到的目标深度都随亮度对比度增加而增加，并取决于亮度相位，但在很大程度上不受亮度视差调制的影响。这些结果验证了这样一种观点，即人类观察者可以利用漫射照明假设仅从亮度梯度感知深度，而无需对光的方向做出假设。对于联合线索的深度判断，观察者对亮度阴影的权重远大于对目标视差调制的权重。结果与根据每个线索单独测量的方差按比例加权的贝叶斯线索组合模型不太相符。相反，它们表明视觉系统使用分离机制来处理这两种类型的信息，而不是根据它们的似然比进行组合。
