In natural scenes, two adjacent surfaces may differ in mean luminance without any sharp change in luminance at their boundary, but rather due to different relative proportions of light and dark regions within each surface. We refer to such boundaries as luminance texture boundaries (LTBs), and in this study we investigate whether LTBs are segmented using different mechanisms than luminance step boundaries (LSBs). We develop a novel method to generate luminance texture boundaries from natural uniform textures, and using these natural LTB stimuli in a boundary segmentation task, we find that observers are much more sensitive to identical luminance differences which are defined by textures (LTBs) than by uniform luminance steps (LSBs), consistent with the possibility of different mechanisms. In a second and third set of experiments, we characterize observer performance segmenting natural LTBs in the presence of masking LSBs which observers are instructed to ignore. We show that although there may be some masking of LTB segmentation by LSBs, it is far less than that observed in a control experiment where both the masker and target are LSBs, and far less than that predicted by a model assuming identical mechanisms. Finally, we perform a fourth set of boundary segmentation experiments using artificial LTB stimuli comprised of differing proportions of white and black dots on opposite sides of the boundary. We find that these stimuli are also highly robust to masking by supra-threshold LSBs, consistent with our results using natural stimuli, and with our earlier studies using similar stimuli. Taken as a whole, these results suggest that the visual system contains mechanisms well suited to detecting surface boundaries that are robust to interference from luminance differences arising from luminance steps like those formed by cast shadows.

中文翻译：

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使用不同的机制分割亮度纹理边界和亮度步长边界

在自然场景中，两个相邻表面的平均亮度可能不同，而在它们的边界处亮度没有任何急剧变化，而是由于每个表面内明暗区域的相对比例不同。我们将此类边界称为亮度纹理边界(LTB)，在本研究中，我们研究了 LTB 是否使用与亮度步长边界不同的机制进行分割(LSB)。我们开发了一种从自然均匀纹理生成亮度纹理边界的新方法，并在边界分割任务中使用这些自然 LTB 刺激，我们发现观察者对由纹理 (LTB) 定义的相同亮度差异比均匀亮度差异更敏感亮度步长 (LSB)，与不同机制的可能性一致。在第二组和第三组实验中，我们描述了在指示观察者忽略的掩蔽 LSB 的情况下分割自然 LTB 的观察者性能。我们表明，虽然 LSB 可能对 LTB 分割进行了一些掩蔽，但它远低于在掩码和目标都是 LSB 的控制实验中观察到的情况，也远低于假设相同机制的模型预测的情况。最后，我们使用人工 LTB 刺激进行第四组边界分割实验，该刺激由边界两侧不同比例的白点和黑点组成。我们发现这些刺激对于超阈值 LSB 的掩蔽也非常稳健，这与我们使用自然刺激的结果以及我们早期使用类似刺激的研究一致。总的来说，这些结果表明，视觉系统包含非常适合检测表面边界的机制，这些机制对由亮度阶跃引起的亮度差异（如由投射阴影形成的亮度阶跃）产生的干扰具有鲁棒性。我们发现这些刺激对于超阈值 LSB 的掩蔽也非常稳健，这与我们使用自然刺激的结果以及我们早期使用类似刺激的研究一致。总的来说，这些结果表明视觉系统包含非常适合检测表面边界的机制，这些机制对由亮度阶跃引起的亮度差异（如由投射阴影形成的亮度阶跃）产生的干扰具有鲁棒性。我们发现这些刺激对于超阈值 LSB 的掩蔽也非常稳健，这与我们使用自然刺激的结果以及我们早期使用类似刺激的研究一致。总的来说，这些结果表明，视觉系统包含非常适合检测表面边界的机制，这些机制对由亮度阶跃引起的亮度差异（如由投射阴影形成的亮度阶跃）产生的干扰具有鲁棒性。