Non-canonical binocular pathways in human vision

人类的大脑将来自许多来源的信息结合在一起，包括我们的两只视野重叠、面向前方的眼睛。这导致了外部世界的单一图像，并为我们提供了立体（3D）视觉。但是，大脑还会因为其他几个原因将眼睛间的信息结合起来。一个例子是我们的瞳孔对光线水平变化的反应——大脑必须使用来自两只眼睛的光线水平来决定瞳孔放大或缩小的程度。这发生在一个与感知完全不同的大脑区域网络中。另外，对动物的研究发现了通往大脑运动敏感区域的直接途径，该区域可能控制着眼球对快速移动物体的自动运动。虽然我们知道这些其他双目通道的解剖结构，但我们对它们的确切作用知之甚少。该项目旨在了解所涉及的计算，并将其与感知途径中的计算进行比较，这些计算已经得到了更好的理解，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身上进行实验。我们的第一个研究将集中在控制瞳孔直径的途径上。我们可以用眼动仪测量瞳孔在闪烁的灯光下是如何收缩和扩张的。这些反应可以与大脑感知部分的反应进行比较，我们同时使用脑电图（EEG，一种记录头皮脑电活动的技术）来测量感知部分。我们的视觉系统包括多个“颜色通道”，这些通道由眼睛中的细胞提供，这些细胞对不同波长的光做出反应。在决定瞳孔反应时，其中一些似乎比其他更重要，因此我们将比较不同通道的双眼组合的特征。我们还将观察这些通道是否在眼睛之间相互作用，例如，如果我们向左右眼显示不同波长的光，不同颜色通道的活动是如何相互作用的？接下来，我们将研究控制自动眼球运动到移动物体的路径的操作。相关的解剖通路可能被特定波长的光（蓝色光，激活s锥通路）直接激活。通过测量眼睛对快速移动刺激的反应，我们可以直接评估不同通道在这一计算中的作用。我们还将直接测量大脑活动，再次使用脑电图，以帮助我们了解控制双眼眼球运动计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一些实验，弱视是一种双眼视力障碍，其中一只眼睛的视力比另一只眼睛的视力要小得多。尽管我们对弱视对感知的影响了解甚多，但可能其他双目通路并未受到影响。了解这一点将有助于未来治疗这种疾病的发展。最后一项研究将使用最先进的脑部扫描仪（MRI和MEG），使用3D投影仪测量大脑对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两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，大脑的活动都是一样的，这与我们的日常观察一致，即两只眼睛睁开时，世界的外观不会发生变化。但我们怀疑，在其他双眼通道中，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。我们将对一系列不同的刺激进行这样的处理，这些刺激是针对特定的通路设计的（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).