Neural pathways underlying human 3D motion perception

我们用眼睛和大脑在周围环境中自信地移动，而不会撞到东西，识别危险或有吸引力的物体，并分析面部表情的细微变化。视觉是一个极其复杂的过程，它使用了大脑的大量资源，并涉及到能量效率、速度和准确性之间的不断权衡。这是如何实现的？回答这个问题的线索来自基础生物学。在解剖学上，令人惊讶的是，视觉系统中有多条通路，不同视觉区域和通路中的神经元似乎对某些类型的视觉信息不同地敏感，如颜色或运动。很明显，一些视觉大脑区域和通路在不同的时间和不同的功能下进化。为不同的功能指定不同的路径可能是降低处理问题复杂性的一种方式--允许大脑并行计算独立的属性。在这里，我们感兴趣的是一组特殊的通路，它们似乎表现出很强的独立性：那些涉及三维空间中运动感知的通路。尽管运动对背侧通路的位置功能至关重要，但很少有人关注双目运动信息是如何处理的，也没有什么通路进行这种处理。在这个项目中，我们探索了关于深度运动(MID)的双目视觉信息是如何通过几种不同的视觉路径来处理和携带的。已经提出了两种利用双目信息进行MID的计算过程，并且有证据表明，每一种方法都对人类视觉有用。这些信号是沿着大脑中不同的基本路径处理的吗？为什么问这个问题很有趣？(1)因为这两种途径都没有被完全理解：以两种方式处理MID所涉及的计算的地点和性质还没有确定。更耐人寻味的是，虽然其中一条路径已经被大量研究，但另一条路径几乎没有被探索，人们对它的了解非常少，而且从进化的角度来看，它可能是古老的。(2)这两条通路可能执行不同的功能，我们提出了一系列的研究来具体探索这些功能可能是什么。我们的项目范围非常广泛，我们从解剖水平上探索了可能的通路的性质，使用功能磁共振成像(FMRI)来定位功能，并使用源成像脑电(EEG)来理解视觉加工的时间动力学。我们将使用心理物理行为研究来研究中间知觉过程中发生的计算过程，使用正常人群来探索正常功能，以及一组临床受试者(斜视性弱视)，我们知道这些受试者使用一种特定的路径损害了中间知觉。此外，使用经颅磁刺激(TMS)来降低特定视觉区域的信息，我们将测试fMRI和EEG确定的中间反应区域的因果相关性。最后，我们还将使用眼球跟踪方法来了解MID信息的特定来源对哪些有用。使用所有这些技术将使我们能够全面了解MID背后的过程。要做到这一点，我们需要三个机构的专业知识，我们将需要主办两个RA，一个具有视觉行为和眼睛跟踪技能，另一个拥有成像证书。这个项目建议的工作主要是核心视觉神经科学。然而，它对人类健康有影响。我们的技术之一将利用这样一个事实，即斜视(斜视性弱视)的人无法使用中间信息的核心来源，即双眼视差。有迹象表明，这组人可能能够使用其他来源的MID。我们小组将是第一个全面探索这一问题的人。

We use our eyes and brain to move confidently within our surroundings without bumping into things, identifying objects as dangerous or attractive and parsing subtle changes in facial expression. Vision is a hugely complex process that uses much of the brain's resources and involves a constant trade-off between energetic efficiency, speed and accuracy. How is this achieved? Clues to answer this question come from fundamental biology. Anatomically, it is striking that there are multiple pathways in the visual system and neurons in different visual areas and pathways appear differentially sensitive to certain types of visual information, such as colour or motion. It is clear that some visual brain areas and pathways have evolved at different times and for different functions. Dedicating different pathways to different functions can be a way of reducing the complexity of the processing problem - allowing the brain to compute independent properties in parallel. Here, we are interested in a specific set of pathways that seem to show strong independence of this type: those involved in the perception of motion in three dimensional space.Whilst motion is known to be critical for the 'where' functions of the dorsal pathway, very little attention has been placed on how binocular information for motion is processed, nor what pathways carry out that processing. In this project we explore how binocular visual information about motion-in-depth (MID) is processed and carried by several different visual pathways. Two computational processes have been proposed for using binocular information for MID, and there is evidence for each of them being useful for human vision. Are these signals processed along different fundamental pathways in the brain? Why is it interesting to ask this question? (1) Because neither pathway is fully understood: the sites and natures of the computations involved in processing MID in two ways have not been identified. Even more intriguingly, while one pathway, has been much studied, the other is barely explored, very poorly understood and potentially ancient, in an evolutionary sense. (2) The two pathways might perform different functions, and we propose a series of studies to specifically explore what those functions might be.Our project has very broad scope, we explore the nature of the putative pathways at the anatomical level, using functional magnetic resonance imaging (fMRI) to localize function, and source-imaged electroencephalography (EEG), which can be used to understand the temporal dynamics of visual processing. We will use psychophysical behavioural studies to study what computational processes take place during MID perception, using both a normal population to explore normal function, and a clinical group of subjects (strabismic amblyopes) that we know have compromised MID processing using one specific pathway. Additionally using Transcranial Magnetic Stimulation (TMS) to degrade information in a particular visual area we will test the causal relevance of MID-responsive regions identified with fMRI and EEG. Finally, we will also employ eye-tracking methods to understand what specific sources of MID information are useful for. Using all these techniques will allow us to get a full picture of the processes underlying MID. To achieve this we require the expertise of three institutions, and we will need to host two RA's, one with visual behavioural and eye tracking skills, the other with imaging credentials.The work proposed in this project is primarily core visual neuroscience. However, it has implications for human health. One of our techniques will exploit the fact that a person with a squint (strabismic amblyopes) is unable to use a core source of MID information, namely binocular disparity. There are hints that this group may be able to use other sources of MID. Our group will be the first to explore this issue comprehensively.