Non-canonical binocular pathways in human vision

人类大脑将来自许多来源的信息结合在一起，包括我们两个向前的眼睛与重叠的视野。这导致外部世界的单一图像，并为我们提供立体（3D）视觉。但大脑也会出于其他几个原因将眼睛中的信息组合起来。一个例子是我们的瞳孔对光线水平变化的反应-大脑必须使用双眼的光线水平来决定瞳孔放大或收缩的程度。这发生在一个完全不同的大脑区域网络中，与那些参与感知的区域不同。另外，对动物的研究发现了一条通往大脑运动敏感区域的直接途径，这可能会控制快速移动物体的自动眼球运动。虽然我们知道这些其他双眼通路的解剖结构，但我们对它们的确切功能了解得很少。本项目旨在理解所涉及的计算，并将其与感知路径中的计算进行比较，后者更容易理解，并且已经存在数学模型。为了实现这一目标，我们将在人类志愿者中进行实验。我们的第一项研究将集中在控制瞳孔直径的途径上。我们可以用眼动仪来测量瞳孔在闪烁的灯光下如何收缩和扩张。这些反应可以与大脑感知部分的反应进行比较，我们同时使用EEG（一种记录头皮脑电活动的技术）进行测量。我们的视觉系统涉及多个“颜色通道”，这些通道由眼睛中对不同波长的光做出反应的细胞提供。其中一些对于决定瞳孔响应似乎比其他更重要，因此我们将比较不同通道的双目组合的特性。我们还将研究通道是否在眼睛之间相互作用，例如，如果我们向左眼和右眼显示不同波长的光，那么不同颜色通道中的活动如何相互作用？接下来，我们将研究控制眼球对运动物体自动运动的通路的运作。所涉及的解剖学途径可以被特定波长的光（蓝色光，激活S-锥途径）直接激活。通过测量响应于呈现给一只或两只眼睛的快速移动刺激的眼球运动，针对特定的颜色路径，我们可以直接评估不同通道在该计算中的贡献。我们还将直接测量大脑活动，再次使用EEG，以帮助我们了解支配双眼运动规划的神经操作的时间过程。我们还将在弱视患者中重复上述实验，弱视是一种双眼视觉障碍，其中一只眼睛对视觉的贡献远远低于另一只眼睛。虽然我们对弱视对知觉的影响了解很多，但可能其他双眼通路不受影响。了解这一点将有助于未来开发这种疾病的治疗方法。最终的研究将使用最先进的大脑扫描仪（MRI和MEG）来测量大脑对使用3D投影仪向一只或两只眼睛显示的图像的反应。在大脑的感知区域，双眼睁开时增加的反应被双眼之间的抑制过程所平衡。这意味着，无论是一只眼睛还是两只眼睛看到刺激，大脑活动都是相同的，这与我们日常观察的结果一致，即当两只眼睛睁开时，世界的外观与一只眼睛相比并没有变化。但我们怀疑，在其他双眼通路中，当两只眼睛都受到刺激时，可能会有更大的增加。因此，我们将寻找对双眼刺激比单眼刺激反应更大的大脑区域。我们将针对一系列不同的刺激来做这件事，这些刺激旨在针对特定的通路（例如运动通路）。

The human brain combines information from many sources, including across our two forward-facing eyes with overlapping visual fields. This results in a single image of the external world, and provides us with stereo (3D) vision. But the brain also combines information across the eyes for several other reasons. One example is the response of our pupils to changes in light levels - the brain must use light levels from both eyes to decide how much to dilate or constrict the pupils. This happens in a completely different network of brain regions to those involved in perception. Separately, studies in animals have found a direct pathway to motion-sensitive regions of the brain, that may govern automatic eye movements to fast moving objects. Although we know about the anatomy of these other binocular pathways, we understand much less about precisely what they are doing. This project aims to understand the computations involved, and to compare them to those in the perceptual pathway, which are better understood, and for which mathematical models already exist.To achieve this, we will perform experiments in human volunteers. Our first study will focus on the pathway that governs pupil diameter. We can measure how the pupils constrict and dilate in response to flickering lights by using an eye-tracker. These responses can be compared to the responses of the perceptual parts of the brain, which we measure at the same time using EEG (a technique that records electrical brain activity at the scalp). Our visual system involves multiple 'colour channels', that are fed by cells in the eye that respond to different wavelengths of light. Some of these appear to be more important than others for deciding the pupil response, so we will compare the characteristics of binocular combination across the different channels. We will also look at whether the channels interact across the eyes, e.g. if we show light of different wavelengths to the left and right eyes, how does activity in the different colour channels interact?Next, we will investigate the operation of the pathway that governs automatic eye movements to moving objects. The anatomical pathways involved may be directly activated by specific wavelengths of light (blue coloured light, that activates the S-cone pathway). By measuring eye movements in response to fast moving stimuli presented to one or both eyes, targeted towards a particular colour pathway, we can directly assess the contribution of different channels in this calculation. We will also measure brain activity directly, again using EEG, to help us understand the timecourse of the neural operations that govern binocular eye movement planning. We will also repeat some of the above experiments in patients with amblyopia, a disorder of binocular vision in which one eye contributes much less to vision than the other. Although we know much about the consequences of amblyopia for perception, it may be that other binocular pathways remain unaffected. Understanding this will aid the development of treatments for this condition in the future.A final study will use state-of-the art brain scanners (MRI and MEG) to measure the response of the brain to images shown to either one or two eyes, using a 3D projector. In the perceptual regions of the brain, the increased response when both eyes are open is balanced by a process of suppression between the eyes. This means that the brain activity is about the same whether one or both eyes see the stimulus, consistent with our everyday observation that the world does not change in appearance when two eyes are open compared to one. But we suspect that in the other binocular pathways, there might be a much bigger increase when both eyes are stimulated. So, we will look for brain regions that give a larger response to binocular stimulation than to monocular stimulation. We will do this for a range of different stimuli that are designed to target specific pathways (e.g. the motion pathway).