Predictive position coding

这个项目研究的是我们如何知道事物的位置，特别是大脑如何编码我们眼前物体的位置。物体的位置是由视觉系统中对其做出反应的细胞明确表示的，因为每个细胞只对视觉世界的一个小区域做出反应，将其位置与眼睛后部视网膜上的一个位置联系起来。然而，这种明确的编码不能解释当眼睛或目标在运动时产生的感知位置的许多戏剧性偏差。在这里，我将建立一个建议，即定位不仅仅是一个简单的注册视网膜的位置补偿头部和眼睛的运动，而是一个复杂的，预测系统，构建可能的目标位置基于各种输入，包括最重要的，目标的当前运动。我们已经展示了这种高级位置编码的两种不同的处理流，一种是基于感知的，另一种与眼球运动有关。为此，我们使用了两种强大的错觉：双重漂移（Lisi & Cavanagh, 2015）和闪光抓取（Cavanagh & Anstis, 2013）。第一种错觉在与目标运动正交的感知位置上产生非常大的位移。值得注意的是，眼球运动不受这种错觉的影响，它们仍然停留在物理位置而不是感知位置上。我们在脑成像方面的初步结果令人惊讶地表明，这种感知错觉出现在大脑的额叶区域，这提高了视觉感知本身是在这个非常高的水平上构建的可能性，而不是在较低的水平上，特别是视觉区域。第二个刺激是在移动的背景上出现的闪光，闪光在运动的方向上被看到。对于这种刺激，眼球运动表现出与感知相同的错觉，这表明闪电抓取刺激可以隔离目标运动的纠正，补偿神经传递的延迟。这种对现在的预测在眼动系统中使用，然后在感知系统中反映出来。这两种刺激产生的位置偏差为研究位置的神经表征提供了一个新的窗口。我建议使用这些刺激来检查感知和运动系统使用的位置代码的基础。许多研究已经解决了空间导航的位置编码问题，这项工作最近获得了诺贝尔奖（O'Keefe, Moser, & Moser, 2014）。相比之下，我们对位置的即时编码知之甚少，而位置编码是这个导航系统的主要输入，至少对人类来说是这样。本研究的目的是研究这种视觉定位编码的机制。这将有助于在临床领域解决影响空间导航和寻路的一般定位障碍，并为构建人工和假体视觉系统的生物医学应用提供指导。

This project addresses how we know where things are, specifically the how the brain codes the positions of objects that we see in front of us. The location of an object is explicitly represented by the cells in the visual system that respond to it, as each cell responds to only one small region of the visual world, linking its position to a location on the retina at the back of the eye. However, this explicit coding cannot explain the many dramatic deviations of perceived location that arise when the eyes or the target are in motion. Here I will build on the proposal that location is not just a simple registration of retinal location with compensation for head and eye movement but is instead a sophisticated, predictive system that constructs probable target locations based a variety of inputs, including most importantly, the target's current motion. We have demonstrated two distinct processing streams for this high-level location coding, one that is perception-based and one that is linked to eye movements. To do so, we have used two powerful illusions: the double-drift (Lisi & Cavanagh, 2015) and the flash-grab (Cavanagh & Anstis, 2013). The first illusion produces a very large displacement in perceived position orthogonal to the motion of the target. Remarkably, eye movements are unaffected by this illusion, they still land on the physical rather than perceived position. Our pilot results in brain imaging suggest surprisingly that this perceptual illusion emerges in the frontal areas of the brain, raising the possibility that visual perception itself is constructed at this very high level rather than in lower level, specifically visual areas. The second stimulus is a flash presented on a moving background where the flash is seen displaced in the direction of motion. For this stimulus, eye movements show the same illusion as perception, suggesting that the flash-grab stimulus can isolate a correction for target motion, compensating for the delays in neural transmission. This prediction of the present is used in the eye movement system and then mirrored in the perceptual system. The position deviations created by these two stimuli offer a new window into the neural representation of location. I propose to use these stimuli to examine the bases of the position code used by perceptual and motoric systems. Numerous studies have addressed the position coding underlying spatial navigation, work that recently won a Nobel prize (O'Keefe, Moser, & Moser, 2014). In contrast, much less is known about the immediate coding of position that is the main input into this navigational system, at least for humans. The goal of the proposed research is to work out the mechanisms of this visual location coding. This will help in the clinical area to address general location disorders affecting spatial navigation and wayfinding as well as providing guidance for biomedical applications in constructing artificial and prosthetic vision systems.