Wallis Thomas S A, Bex Peter J
Schepens Eye Research Institute, Massachusetts Eye and Ear Infirmary, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA.
J Vis. 2012 Jul 13;12(7):6. doi: 10.1167/12.7.6.
Visual crowding is the inability to identify visible features when they are surrounded by other structure in the peripheral field. Since natural environments are replete with structure and most of our visual field is peripheral, crowding represents the primary limit on vision in the real world. However, little is known about the characteristics of crowding under natural conditions. Here we examine where crowding occurs in natural images. Observers were required to identify which of four locations contained a patch of "dead leaves'' (synthetic, naturalistic contour structure) embedded into natural images. Threshold size for the dead leaves patch scaled with eccentricity in a manner consistent with crowding. Reverse correlation at multiple scales was used to determine local image statistics that correlated with task performance. Stepwise model selection revealed that local RMS contrast and edge density at the site of the dead leaves patch were of primary importance in predicting the occurrence of crowding once patch size and eccentricity had been considered. The absolute magnitudes of the regression weights for RMS contrast at different spatial scales varied in a manner consistent with receptive field sizes measured in striate cortex of primate brains. Our results are consistent with crowding models that are based on spatial averaging of features in the early stages of the visual system, and allow the prediction of where crowding is likely to occur in natural images.
视觉拥挤是指当视野周边的可见特征被其他结构包围时，无法识别这些特征。由于自然环境中充满了各种结构，且我们大部分视野都位于周边区域，因此拥挤现象是现实世界中视觉的主要限制因素。然而，对于自然条件下拥挤现象的特征，我们所知甚少。在此，我们研究了自然图像中拥挤现象发生的位置。要求观察者识别自然图像中四个位置中的哪一个包含嵌入的一片“枯叶”（合成的、具有自然主义轮廓的结构）。枯叶斑块的阈值大小随偏心率变化，其方式与拥挤现象一致。我们使用多尺度反向相关来确定与任务表现相关的局部图像统计量。逐步模型选择表明，一旦考虑了斑块大小和偏心率，枯叶斑块位置的局部均方根对比度和边缘密度在预测拥挤现象的发生方面最为重要。不同空间尺度下均方根对比度回归权重的绝对值变化方式与在灵长类动物大脑纹状皮层中测量的感受野大小一致。我们的结果与基于视觉系统早期阶段特征空间平均的拥挤模型一致，并能够预测自然图像中可能发生拥挤现象的位置。
