Seeing the world in a different light - discovering how vertebrates see polarized light

大多数动物看待世界的方式与我们截然不同，它们看清细节、运动和颜色的能力也不同。这项研究将研究视觉的一个方面，除了这些熟悉的视觉特性之外，还有一个我们完全陌生的方面：看到偏振光的能力。偏振描述了一波光振荡的方向，尽管人类没有意识到这一点，但我们周围的光是偏振的。偏振视觉通常被认为是昆虫等无脊椎动物的特征，但许多脊椎动物也可以检测和解码光的偏振。这为它们提供了额外的视觉信息，用于执行目标识别、通信和伪装检测等任务。它还增加了其他感官能力的额外维度，如用于导航的嗅觉或磁接收，并有可能在光线散射的环境中增强对比度，特别是在水下。在这项拟议的研究中，我们将以鱼类为模式生物，研究脊椎动物的偏振视觉。有几种鱼被展示了将光的偏振信息从眼睛传递到大脑。然而，对于眼睛检测光的偏振的方式，或者鱼如何利用它的行为，我们知之甚少。我们的实验建立在PI最近的工作基础上，他最近也是第一次表明，当脊椎动物视网膜中特定类型的光敏细胞(称为视锥细胞)在眼睛内被端面照射时，它们会不同程度地吸收不同方向的线偏振光。我们的测量将通过显微分光光度法和显微光谱偏振法进行-这两种技术测量偏振光如何被吸收并通过微观大小的样品。我们将使用两种显微分光光度技术：(I)使用传统仪器，其中单个细胞以侧面方向测量，以验证来自(Ii)创新和专门构建的二维成像仪器的数据，该仪器将允许同时测量视网膜中的许多细胞。随着新的显微光谱偏振测量，通过采用2-D显微分光光度计，我们将确定已知具有不同视网膜解剖结构(例如，视网膜中视锥的方形或线性排列)和视锥感光类型的不同互补(例如，具有和不具有紫外线敏感视锥的物种)如何吸收偏振光。我们将把这些光谱测量与电子显微镜研究结合起来，以量化锥细胞外节中蛋白质和脂类的组织，我们认为这很可能是使单个光感受器对不同偏振光敏感的机制。锥体吸收光的部分已经被证明具有未知的组织亚结构，但这种结构对光感受器功能的意义尚未被证明。最后，我们将使用行为测试来筛选不同种类的鱼，以进行极化视觉的行为演示，这是任何感官能力的重要终点。鱼很容易学习产生奖励的视觉任务，比如食物，我们将利用这一属性来测试偏振敏感性。通过使用一种新的方法，基于结合向列液晶单元的设备来控制鱼在实验中看到的刺激的偏振，我们将研究它们区分水平和垂直偏振的能力；紫外光在偏振视觉中的重要性；以及可以看到偏振变化的频率或速度。最终，这项研究将回答视觉生物学中最重要的悬而未决的问题之一：脊椎动物如何看到偏振光？

Most animals see the world in a very different way from us and differ in their ability to see detail, movement and colour. This study will investigate an aspect of vision beyond these familiar visual properties, and one that is totally alien to us: the ability to see polarized light. Polarization describes the direction in which a wave of light oscillates and, although humans are unaware of this, light around us is polarized. Polarization vision is often considered a characteristic of invertebrates such as insects, but many vertebrates can also detect and decode the polarization of light. This gives them extra visual information for tasks such as object recognition, communication and camouflage detection. It also adds an extra dimension to other sensory abilities, such as smell or magnetoreception for use in navigation and has potential to enhance contrasts in environments where light is scattered, particularly underwater. In this proposed research, we will investigate polarization vision in vertebrates, using fish as model organisms. Several species of fish have been shown relay information about the polarization of light from the eye to the brain. However, very little is known about either the way the eye detects the polarization of light, or how fish use it in their behaviour. Our experiments build on the work of the PI who recently, and for the first time, showed that when particular types of light sensitive cells in vertebrate retina (called cones) were illuminated end on, as they are in the eye, they absorb differently-orientated linear polarized light to different degrees. Our measurements will be made by microspectrophotometry and microspectropolarimetry - techniques that measure how polarized light is absorbed and transmitted through microscopic-sized samples. We will use two techniques for microspectrophotometry: (i) using a conventional instrument in which single cells are measured in a side-on orientation to validate data from (ii) an innovative and specifically constructed 2-dimensional imaging instrument that will allow the simultaneous measurement of many cells in a retina. Along with novel microspectropolarimetric measurements, made by adapting the 2-D microspectrophotometer, we will determine how species known to have different retinal anatomies (e.g. square or linear arrangements of cones in their retinas) and different complements of cone photoreceptor types (e.g. those with and without UV-sensitive cones) absorb polarized light. We will ally these spectral measurements with electron microscopy studies to quantify the organization of proteins and lipids in cone cell outer segments which we suggest may well be the mechanism that enables individual photoreceptors to be sensitive to differently polarized light. The part of cones that absorb light have already been shown to have unexplained organizational sub-structure, but the significance of such structures for photoreceptor function has yet to be demonstrated. Finally, we will use behavioural tests to screen various species of fish for behavioural demonstration of polarization vision, this being the important end point of any sensory capability. Fish readily learn visual tasks that result in a reward such as food and we will use this attribute to test for polarization sensitivity. By using a novel method based on apparatus incorporating nematic liquid crystal cells to control the polarization of the stimulus that the fish see in the experiments, we will investigate their ability to discriminate horizontal from vertical polarization; the importance of ultraviolet light in polarization vision; and the frequency, or speed, with which changes in polarization can be seen. Ultimately this research will answer one of the most significant unanswered questions in vision biology: How do vertebrates see polarized light?