Computational Perception Laboratory, Florida Gulf Coast University, Fort Myers, FL 33965-6565, USA; Department of Psychology, Florida Gulf Coast University, Fort Myers, FL 33965-6565, USA.
Vision Res. 2022 Jan;190:107968. doi: 10.1016/j.visres.2021.107968. Epub 2021 Nov 15.
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 there is very little effect of masking LSBs on LTB segmentation performance. Furthermore, any masking effects we find are far less than those observed in a control experiment where both the masker and target are LSBs, and far less than those 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.
在自然场景中，两个相邻的表面可能在亮度上存在差异，但其边界处的亮度没有明显变化，而是由于每个表面内的亮区和暗区的相对比例不同。我们将这种边界称为亮度纹理边界（LTB），在本研究中，我们研究了 LTB 是否使用与亮度阶跃边界（LSB）不同的机制进行分割。我们开发了一种从自然均匀纹理中生成亮度纹理边界的新方法，并使用这些自然 LTB 刺激在边界分割任务中，我们发现观察者对由纹理（LTB）定义的相同亮度差异比由均匀亮度阶跃（LSB）定义的亮度差异更为敏感，这与使用不同机制的可能性一致。在第二组和第三组实验中，我们在存在掩蔽 LSB 的情况下对观察者被指示忽略的自然 LTB 进行分割，描述了观察者的表现。我们表明，掩蔽 LSB 对 LTB 分割性能的影响非常小。此外，我们发现的任何掩蔽效应都远小于在控制实验中观察到的掩蔽效应，在该控制实验中，掩蔽和目标都是 LSB，也远小于假设使用相同机制的模型所预测的掩蔽效应。最后，我们使用由边界两侧的白点和黑点组成的不同比例的人工 LTB 刺激进行了第四组边界分割实验。我们发现这些刺激对超过阈值的 LSB 的掩蔽也非常稳健，这与我们使用自然刺激的结果一致，也与我们之前使用类似刺激的研究一致。总的来说，这些结果表明，视觉系统包含了很好的机制，可以检测到表面边界，这些边界对来自亮度阶跃（如投射阴影形成的亮度阶跃）引起的亮度差异的干扰具有鲁棒性。
