The representation and processing of contour and surface in the human brain

在过去的二十年里，视觉脑已经被功能性磁共振成像（fMRI）询问，提供了对其组织的重要见解。较早的处理发生在后部，“较低级别”的视觉大脑区域，其中包含明确的视野地图。这些区域是通过使用系统地移动通过视野的视觉刺激来“映射”的，同时记录大脑的反应。技术的进步使得越来越多的视觉大脑可以以这种方式进行映射。另一种绘制视觉大脑组织的方法是测试刺激的选择性，通常是通过对比大脑对两个或更多离散刺激类别的反应。这种方法已经确定了“更高级别”的类别选择区域，例如被称为外侧枕叶复合体的形状选择区域。最初认为类别选择区域很少或没有明确的视野映射。然而，随着更多的视野地图被发现，一些被发现与类别选择区域重叠，这意味着这两个组织并不相互排斥。我们将把这些重叠区域称为“中级”视野图。这两个组织原则的交叉给了我们一个机会来理解视觉大脑是如何从低级处理过渡到高级处理的。这样的过渡点应该产生有价值的见解表示的“抽象”的信息在更高级别的areages.Despite其潜在的重要性，对这些中级区域的研究很少存在。我们的目标是解决这个问题，重点是了解的角色“中级”视觉区发挥。我们已经发表的证据表明，中级区域可以代表抽象信息，但在这个级别所代表的信息的性质和表征本身的性质仍然未知。因此，我们的首要目标是找出哪些视觉信息是被处理的，以及这些信息是如何在视觉系统的中间层被呈现出来的，我们将重点关注的中间层视觉区域集中在外侧枕叶皮层。同时，我们也将评估位于枕叶皮层背侧和腹侧的视野图，以验证我们测量的任何影响都是不可分离的。令人欣慰的是，使用这种策略，我们已经发现，某些抽象表征存在于外侧，而不是腹侧或背侧的中层区域。因此，我们预计，我们的工作将再次表现出可分离的影响，在中层areas.Our工作意味着，枕外侧区的过程方面的轮廓曲率，我们的目标是进一步完善我们的理解，这些表示。我们已经有了等高线处理某些方面的试验数据，因此相信所提议的工作有很大的成功机会。然而，与此同时，我们希望探索3D表面曲率的处理和表示，以确定这些属性是否具有共享或独特的神经基础。这项工作的风险更高，但它的回报可能是巨大的，因为它代表了第一次有机会将轮廓和表面的研究结合起来，并了解它们对我们对物体的感知的相对贡献是如何在人脑中实现的。我们将联合收割机结合感知测量和功能磁共振成像，以揭示人脑如何处理和表示轮廓和表面曲率。知觉实验将揭示我们的刺激操作是如何被感知的;确定在神经成像实验期间将呈现哪些刺激。这两种方法都将利用我们在刺激控制方面的专业知识，这是基于可以从轮廓到表面进行概括的计算方法。此外，我们已经证明，我们可以用感知和物理指标来描述我们的刺激，这些指标可以解释中级视觉区域的反应模式，这种方法将在拟议的工作中得到扩展。

The visual brain has been interrogated with functional magnetic resonance imaging (fMRI) over the last twenty years, providing significant insight into its organisation. Earlier processing occurs in posterior, 'lower-level' visual brain areas, which contain explicit visual field maps. Such areas are 'mapped' by using visual stimuli that systematically move through the visual field, whilst recording the brain responses. Improvements in techniques have allowed an increasing extent of the visual brain to be mapped in this manner. An alternative method to chart the visual brain's organisation is to test for stimulus selectivity, typically by contrasting the brain's responses to two or more discrete stimulus categories. This approach has identified 'higher-level' category selective areas, for example a shape-selective region referred to as the lateral occipital complex.It was first thought that category selective regions had little or no explicit mapping of the visual field. However, as more visual field maps were discovered some were found to overlap with category selective regions, implying that the two organizations are not mutually exclusive. We will refer to these overlapping regions as 'mid-level' visual field maps. The fact that the two organizing principles intersect gives us an opportunity to understand how the visual brain transitions from low-to-high level processing. Such transitional points should yield valuable insights into the representation of 'abstract' information in higher-level areas.Despite their potential importance, little research on these mid-level regions exists. We aim to address this by focusing on understanding the roles 'mid-level' visual areas play. We have published evidence that mid-level areas can represent abstract information, but the nature of the information represented at this level and the nature of the representations themselves remain unknown. Our overarching aim, therefore, is to find out what visual information is processed and how it represented at this mid-level of the visual system.The mid-level visual areas we will focus on cluster in lateral occipital cortex. At the same time we will also assess visual field maps that lie in dorsal and ventral occipital cortex, to verify that any effects we measure are dissociable. Reassuringly, using this strategy we have already found that certain abstract representations are found in lateral, but not ventral or dorsal mid-level areas. We anticipate therefore that our work will again exhibit dissociable effects in mid-level areas.Our work implies that lateral occipital areas process aspects of contour curvature; we aim to further refine our understanding of these representations. We already have pilot data on some aspects of contour processing and believe therefore that much of the proposed work has a high chance of success. At the same time however we want to explore the processing and representation of 3D surface curvature, to determine whether such properties have shared or unique neural underpinnings. This work is higher risk, but its return could be large as it represents the first opportunity to bring together the study of contour and surface and learn how their relative contributions to our perception of objects is achieved in the human brain.We will combine perceptual measurements and fMRI to reveal how the human brain processes and represents contour and surface curvature. The perceptual experiments will reveal how our stimulus manipulations are perceived; determining which stimuli will be presented during neuroimaging experiments. Both approaches will leverage our expertise in stimulus control, which is grounded in computational methods that can generalize from contour to surface. Further, we have demonstrated that we can characterize our stimuli with perceptual and physical metrics that explain patterns of response in mid-level visual areas and this approach will be extended in the proposed work.