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

大多数动物看世界的方式与我们非常不同，它们看细节、运动和颜色的能力也不同。这项研究将探讨视觉的一个方面，超越这些熟悉的视觉特性，一个完全陌生的我们：看到偏振光的能力。偏振描述了光波振荡的方向，尽管人类没有意识到这一点，但我们周围的光是极化的。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探测和解码光的偏振。这为它们提供了额外的视觉信息，用于诸如物体识别、通信和伪装探测等任务。它还为其他感官能力增加了额外的维度，比如用于导航的嗅觉或磁感，并有可能在光线散射的环境中增强对比度，尤其是在水下。在本研究中，我们将以鱼类为模式生物，研究脊椎动物的偏振视觉。研究表明，有几种鱼类能够将眼睛发出的光的偏振信息传递给大脑。然而，人们对眼睛探测光线偏振的方式以及鱼类如何利用这种方式进行行为知之甚少。我们的实验建立在PI的工作基础上，PI最近首次表明，当脊椎动物视网膜中特定类型的光敏细胞（称为视锥细胞）像在眼睛中一样被照射时，它们会在不同程度上吸收不同方向的线偏振光。我们的测量将通过微分光光度法和微光谱偏振法进行，这两种技术测量了偏振光如何被吸收和通过显微镜大小的样品传输。我们将使用两种显微分光光度计技术：(i)使用传统仪器，其中单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，该仪器将允许同时测量视网膜中的许多细胞。随着新的微光谱偏振测量，通过适应2-D显微分光光度计，我们将确定如何物种已知有不同的视网膜解剖结构（例如，正方形或线性排列的视锥细胞在他们的视网膜）和不同的视锥光感受器类型的补充（例如，那些有和没有紫外线敏感的视锥细胞）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，量化锥体细胞外段蛋白质和脂质的组织，我们认为这可能是使单个光感受器对不同偏振光敏感的机制。锥细胞吸收光的部分已经被证明具有无法解释的组织子结构，但这种结构对光感受器功能的意义尚未得到证实。最后，我们将使用行为测试来筛选各种鱼类的极化视觉行为演示，这是任何感官能力的重要终点。鱼很容易学会视觉任务，从而获得奖励，如食物，我们将使用这一属性来测试偏振敏感性。通过采用一种新颖的方法，结合向列液晶细胞的装置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我们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：脊椎动物是如何看到偏振光的？

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?