Orger Michael B, Baier Herwig
Department of Physiology, Program in Neuroscience, University of California--San Francisco, 94143, USA.
Vis Neurosci. 2005 May-Jun;22(3):275-81. doi: 10.1017/S0952523805223039.
Visual systems break scenes down into individual features, processed in distinct channels, and then selectively recombine those features according to the demands of particular behavioral tasks. In primates, for example, there are distinct pathways for motion and form processing. While form vision utilizes color information, motion pathways receive input from only a subset of cone photoreceptors and are generally colorblind. To explore the link between early channeling of visual information and behavioral output across vertebrate species, we measured the chromatic inputs to the optomotor response of larval zebrafish. Using cone-isolating gratings, we found that there is a strong input from both red and green cones but not short-wavelength cones, which nevertheless do contribute to another behavior, phototaxis. Using a motion-nulling method, we measured precisely the input strength of gratings that stimulated cones in combination. The fish do not respond to gratings that stimulate different cone types out of phase, but have an enhanced response when the cones are stimulated together. This shows that red and green cone signals are pooled at a stage before motion detection. Since the two cone inputs are combined into a single 'luminance' channel, the response to sinusoidal gratings is colorblind. However, we also find that the relative contributions of the two cones at isoluminance varies with spatial frequency. Therefore, natural stimuli, which contain a mixture of spatial frequencies, are likely to be visible regardless of their chromatic composition.
视觉系统将场景分解为各个特征，在不同通道中进行处理，然后根据特定行为任务的需求有选择地重新组合这些特征。例如，在灵长类动物中，存在用于运动和形状处理的不同通路。形状视觉利用颜色信息，而运动通路仅从一部分视锥光感受器接收输入，并且通常是色盲的。为了探究脊椎动物物种中视觉信息的早期通道化与行为输出之间的联系，我们测量了斑马鱼幼体视动反应的色觉输入。使用分离视锥的光栅，我们发现红色和绿色视锥都有很强的输入，但短波长视锥没有，不过短波长视锥确实对另一种行为——趋光性有贡献。使用运动抵消方法，我们精确测量了组合刺激视锥的光栅的输入强度。斑马鱼对异相刺激不同视锥类型的光栅没有反应，但当视锥一起受到刺激时反应增强。这表明红色和绿色视锥信号在运动检测之前的一个阶段合并。由于两个视锥输入被组合成一个单一的“亮度”通道，对正弦光栅的反应是色盲的。然而，我们还发现，在等亮度条件下，两个视锥的相对贡献随空间频率而变化。因此，包含多种空间频率混合的自然刺激，无论其颜色组成如何，都可能是可见的。
