Object, face, body and scene representations in the human brain

这项研究的目的是了解我们如何看到我们所看到的：大脑如何分析落在眼睛视网膜上的光线，以编码一个充满物体，人和事物的世界？ 在过去的一年里，我们专注于1）大脑中自下而上（感觉驱动）和自上而下（内部驱动）处理之间的关系，重点是从记忆中检索信息，以及2）复杂视觉刺激的感知，最近关注视觉场景。 1)自下而上与自上而下处理（方案93-M-0170，NCT 00001360） 我们的视觉感知是自下而上的感官信息和自上而下的内部生成信号之间相互作用的产物，这些信号引导对输入的解释并反映我们的先验知识和意图。 我们之前已经证明，在视觉心理意象过程中，在视觉皮层中观察到的反应模式可以用来解码一个人正在想象的对象。此外，这些模式类似于在感知相同物体时观察到的模式。在过去的一年里，我们一直在研究皮层中视觉活动的重演是否取决于提取是来自短期记忆还是长期记忆以及海马体的参与。 我们向参与者展示日常物品的图像（例如头盔，灯，沙发），并要求他们尽可能生动地记住这些物品。在30分钟（短期）或一天（长期）的延迟后，我们使用MRI测量了参与者的大脑活动，因为参与者被提示想象他们学到的特定对象。 首先，复制我们之前的工作，我们发现在视觉皮层中，经过短暂的延迟，我们可以解码参与者想象的特定物体。 在延迟一天后也是如此，这表明活动的重演并不是从短期记忆中提取的特有现象。第二，在海马体中，我们发现反应模式也可以用来解码正在检索的对象，但只有在一天之后，而不是在短暂的延迟之后。后一个结果表明，海马体中特定信息的表达依赖于一个耗时的过程。 2)感知真实的世界场景（方案93-M-0170，NCT 00001360） 现实世界的场景是非常复杂和异构的，但我们能够毫不费力地识别和分类它们。虽然先前的研究已经确定了几个似乎专门用于场景处理的大脑区域，但仍然不清楚这些不同区域的确切作用。 在我们最近提出的视觉处理的一般框架的基础上，我们一直在研究外侧和腹侧枕颞皮层上的两个主要场景选择区域显示不同视网膜定位特性的程度，这反映了视觉皮层的大规模结构（Silson等人，2015）。通过将场景片段呈现给视野的特定部分，我们已经证明了横向场景选择区域偏向于较低的视野，而腹侧场景选择区域偏向于较高的视野。这些结果突出了海拔作为一个组织原则，在高层次的视觉皮层的重要性，并建议这两个场景区域可能反映单独的类别选择性表示的不同部分的视野，而不是单独的阶段，在一个串行的，层次化的途径。 阐明大脑如何使我们能够识别物体，场景，面孔和身体，为我们对周围世界的内部表征的本质提供了重要的见解。理解这些表征对于试图确定许多精神健康和神经系统疾病的潜在缺陷至关重要。

The goal of this research is to understand how we see what we see: how does the brain analyze the light falling on the retina of the eye to encode a world full of objects, people and things? During the past year we have focused on 1) the relationship between bottom up (sensory driven) and top-down (internally driven) processing in the brain, focusing on the retrieval of information from memory, and 2) perception of complex visual stimuli, focusing most recently on visual scenes. 1) Bottom up versus top down processing (Protocol 93-M-0170, NCT00001360) Our visual perception is the product of an interaction between bottom-up sensory information and top-down, internally generated signals guiding interpretation of the input and reflecting our prior knowledge and intent. We have previously demonstrated that during visual mental imagery, the patterns of response observed in visual cortex can be used to decode what object a person is imagining. Further, those patterns are similar to those observed during perception of the same objects. Over the past year we have been investigating whether such recapitulation of visual activity in cortex is dependent on whether the retrieval is from short- or long-term memory and the involvement of the hippocampus. We presented participants with images of every day objects (e.g. helmet, lamp, couch) and asked them to remember those items as vividly as possible. After a delay of either 30 minutes (short-term) or one day (long-term), we measured brain activity using MRI as participants were cued to imagine specific objects they had learned. First, replicating our prior work, we found that in visual cortex after short delays, we could decode the specific object participants were imagining. The same was true after a delay of one day suggesting that the recapitulation of activity is not specific to retrieval from short-term memory. Second, in hippocampus, we found that the patterns of response could also be used to decode the object being retrieved, but only after one day and not after a short delay. This latter result suggests that the representation of specific information in hippocampus is dependent on a time-consuming process. 2) Perception of real world scenes (Protocol 93-M-0170, NCT00001360) Real-world scenes are incredibly complex and heterogeneous, yet we are able to identify and categorize them effortlessly. While prior studies have identified several brain regions that appear to be specialized for scene processing, it remains unclear exactly what the precise roles of these different regions are. Building on a general framework for visual processing we proposed recently, we have been investigating the extent to which the two major scene-selective regions on lateral and ventral occipitotemporal cortex show different retinotopic properties reflecting a large-scale architecture of visual cortex (Silson et al., 2015). By presenting fragments of scenes to specific portions of the visual field we have demonstrated that the lateral scene-selective region is biased towards the lower visual field while the ventral scene-selective region is biased towards the upper visual field. These results highlight the importance of elevation as an organizing principle in high-level visual cortex and suggest that these two scene regions may reflect separate category-selective representations of distinct portions of the visual field rather then separate stages in a serial, hierarchical pathway. Elucidating how the brain enables us to recognize objects, scenes, faces and bodies provides important insights into the nature of our internal representations of the world around us. Understanding these representations is vital in trying to determine the underlying deficits in many mental health and neurological disorders.