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Encoding of natural images by retinal ganglion cells.

机译：视网膜神经节细胞对自然图像的编码。

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摘要

Natural scenes have many special statistical properties that have shaped our visual system through natural evolution. It may thus be necessary to use natural images directly to examine retinal-ganglion-cells' (RGCs) properties, rather than to extrapolate their properties from artificial stimuli. In this study, we first inspected what the most important visual property determining the responses of an RGC to natural images is. A new method was developed to estimate with natural images the sizes of the receptive-field (RF) center and surround. We showed that the center sizes estimated with our method were similar to those obtained with standard artificial stimuli. Furthermore, the temporal mean contrast of the center of the RFstrongly dominated the RGC's responses, while surround contrast mostly showed a weak and division-like (as opposed to subtractive) inhibition. We then asked whether the RGCs' responses also depend on the local visual textures of natural images, or the luminance variation from the mean. We observed that RGCs responded asymmetrically between the transition from homogeneous backgrounds to natural images (onset), and the reverse transition (offset), even if both transitions had the same local temporal mean contrast. Furthermore, the negative of the natural images inverted this asymmetry, and their histogram equalization eliminated it. Hence, the response asymmetry arose from the asymmetric intensity distribution in the natural images. We further developed a method, spike-triggered contrast histogram (STCH), to demonstrate that a natural image with strong visual texture tended to elicit larger responses than one with weak texture. To account for these results, a nonlinear-linear model was developed. It included multiple subunits of nonlinear inputs, each covering a sub-region of the RF. Finally, we investigated whether the RGCs' responses adapt to the spatial and temporal contrasts of natural images. We found that RGCs displayed a variety of contrast-adaptation types across the population when responding to a step mean-contrast change of natural images, and that their contrast adaptation depended on the natural-image contrast difference. Thus, multiple biophysical mechanisms might be involved in RGCs' contrast adaptation, and different RGC types might use a distinct subset of these mechanisms for different visual tasks.
机译：自然场景具有许多特殊的统计属性，这些属性通过自然演化塑造了我们的视觉系统。因此，可能有必要直接使用自然图像来检查视网膜神经节细胞（RGC）的特性，而不是从人工刺激中推断其特性。在这项研究中，我们首先检查了确定RGC对自然图像的响应的最重要的视觉属性是什么。开发了一种新方法来估计具有自然图像的接收场（RF）中心和周围区域的大小。我们表明，用我们的方法估算的中心大小与使用标准人工刺激获得的中心大小相似。此外，RF中心的时间平均对比度在RGC的响应中占主导地位，而周围对比度则大多表现出微弱的分裂状（与减法相反）抑制。然后，我们询问RGC的响应是否还取决于自然图像的局部视觉纹理，还是取决于平均值的亮度变化。我们观察到，即使两个过渡具有相同的局部时域平均对比度，RGC在从均质背景到自然图像的过渡（起始）和反向过渡（偏移）之间也存在不对称响应。此外，自然图像的负片使这种不对称性反过来，并且它们的直方图均衡消除了它。因此，响应不对称是由自然图像中的不对称强度分布引起的。我们进一步开发了一种方法，即尖峰触发对比度直方图（STCH），以证明具有强视觉纹理的自然图像比具有弱纹理的图像倾向于引起更大的响应。为了说明这些结果，开发了非线性线性模型。它包括非线性输入的多个子单元，每个子单元覆盖RF的一个子区域。最后，我们研究了RGC的响应是否适应自然图像的时空对比。我们发现，RGC在响应自然图像的阶跃平均对比度变化时会在人群中显示多种对比度适应类型，并且它们的对比度适应性取决于自然图像的对比度差异。因此，RGC的对比度适应可能涉及多种生物物理机制，并且不同的RGC类型可能将这些机制的不同子集用于不同的视觉任务。

著录项

  • 作者

    Cao, Xiwu.;

  • 作者单位

    University of Southern California.;

  • 授予单位 University of Southern California.;
  • 学科 Biology Neuroscience.;Engineering Biomedical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 125 p.
  • 总页数 125
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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