Spectral circuits for figure-ground segmentation in motion vision

我们将阐明“颜色”信息在支持运动视觉中的作用。眼睛的这两种基本能力通常被单独考虑。然而，无论是从光如何在水中传播的基本物理，还是从视觉的进化来看，这两者肯定是从根本上交织在一起的。视觉最先是在水中进化的。首先是光敏感度，这是由大约8亿年前视蛋白的进化实现的。不久之后，可能出现了一种基本的“色觉”，这是由于视蛋白的多样化，形成了对不同波长(“颜色”)光敏感的变体。原始动物很可能已经能够使用这种新发现的感觉来辨别周围环境的“颜色”，尽管不知道它的空间结构--毕竟，成像视觉还没有进化出来，这需要光感受器、屏幕色素和眼睛光学的有序阵列。然而，即使没有空间知识，颜色本身也是有用的。例如，它可以告知水的深度：来自太阳的光以一种“颜色相关”的方式穿透水：蓝光和紫外光迅速消失，而绿光和红光穿透得更深。因此，如果环境是蓝色/紫外线丰富的，你很有可能接近地表。还需要大约2.5亿年的时间，早期的“色觉”系统才会进化成完全飞行的眼睛。这一关键步骤可能发生在大约5.4亿年前的寒武纪大爆发期间，当时人们认为，新发现的“成像视觉”意识集中促成了我们今天所知的神经复杂动物生命的出现。突然间，动物可以用眼睛更有效地导航周围环境，稳定身体，并在视觉上发现潜在的猎物和捕食者。这些新发现的能力是由我们早期祖先眼睛和大脑中计算视觉场景中复杂类型信息的新神经电路实现的。也许最关键的是感知运动的能力。背景的运动将告诉动物它们自己是如何在环境中移动的，而前景的运动将突出潜在的附近对象以进行交互。动物必须能够区分这两者。这通常被认为是通过相对复杂且远未被理解的视网膜和大脑回路实现的，这些回路不断比较视觉空间不同部分随着时间的亮度变化。然而，回过头来看，我们最早的祖先是如何简单地根据周围环境的“颜色”来判断水深的，同样的基本物理学原理也应该同样适用于判断水中物体的距离。换句话说，一个物体的“颜色”本身就应该告诉动物它是近是远。更重要的是，由于“颜色”视觉几乎肯定早于运动视觉，因此实现运动视觉的回路必然要在已有的色彩回路的基础上进化。如果颜色信息没有从根本上嵌入提取视觉运动的电路中，那将是非常令人惊讶的，包括在今天仍然活着的动物中。目标。我们将致力于实验中的可听从的幼虫斑马鱼，这种斑马鱼可以不受限制地通过光学接触到活动物的眼睛和大脑的任何部分，这些斑马鱼生活在与视觉最初进化的世界没有太大区别的浅水淡水中。我们将结合来自野外的视频数据、行为观察、视网膜电路的遗传操作以及一次1,000个单个神经细胞的最先进的神经生理学记录来询问斑马鱼是否以及如何使用颜色信息来进行运动视觉。了解颜色和运动视觉系统的真正进化起源和可能的相互作用，将从非常普遍的意义上了解“视觉”是如何工作的，包括在我们自己的眼睛中。

We will elucidate the role of "colour" information in supporting motion vision. These two fundamental abilities of eyes are usually considered in isolation. However, both from basic physics of how light travels in the water, and from looking at the evolution of vision, the two must be fundamentally entwined.Background. Vision evolved first in the water. First came light sensitivity, enabled by the evolution of opsins some 800 million years ago. Soon after probably came a rudimentary sense of "colour vision", enabled by the diversification of opsins into variants that were sensitive to different wavelengths ("colours") of light. Primitive animals likely would have been able to use this newfound sense to tell the "colour" of their surroundings, albeit without knowing its spatial structure - after all, image forming vision, requiring ordered arrays of photoreceptors, screening pigment and eye optics had not yet evolved. Nevertheless, even without knowledge of space, colour alone can be useful. For example, it can inform about water depth: Light from the sun penetrates water in a "colour-dependent" manner: Blue and UV light is rapidly lost, while green and red light penetrates much deeper. Accordingly, if the environment is blue/UV-rich, chances are you are near the surface.It would take another ~250 or so million years before early "colour-vision" systems would evolve into full-flown eyes. This critical step probably happened some 540 million years ago during the Cambrian explosion, when a newly found sense of "image forming vision" is thought to have centrally enabled the emergence of neurally complex animal life as we know it today. Suddenly, animals could use their eyes to navigate their surroundings much more efficiently, stabilise their bodies, and visually spot potential prey and predators. These newfound abilities were made possible by new neural circuits within the eyes and brains of our early ancestors that computed complex types of information in the visual scene. Perhaps most critical of all was the ability to sense motion. Motion of the background would tell animals how they themselves were moving through the environment, while motion of the foreground would highlight potential nearby objects to interact with. Animals must be able to be able to tell the two apart. This is generally thought to be achieved by relatively complex and far from understood circuits of the retina and brain that constantly compare brightness changes over time across different parts of visual space. However, looking back at how our very earliest ancestors might have told water depth simply based on the "colour" of their surroundings, the very same principle of basic physics should serve equally well to tell the distance of objects in the water. In other words, the "colour" of an object alone should tell animals if it is near, or far. What is more, since "colour" vision almost certainly predates motion vision, circuits enabling the latter would have necessarily had to evolve on top of pre-existing colour circuits. It would then be very surprising indeed if colour information were not fundamentally inbuilt into circuits that extract visual motion, including in animals that are alive today. Objectives. We will work on the experimentally amenable larval zebrafish which allow unrestricted optical access to any part of the eyes and brains in the live animal, and which inhabit shallow freshwaters not too dissimilar from the world where vision first evolved. We will combine videography data from the field, behavioural observations, genetic manipulations of retinal circuits, and state-of-the-art neurophysiological recordings of 1,000s of individual nerve cells at a time to ask if and how zebrafish use colour information for motion vision.Impact. Understanding the true evolutionary origins and possible interplay of colour and motion vision systems will inform how "vision" works in a very general sense, including in our own eyes.