The use of prior assumptions in human visual processing.

当我们观察世界时，光线进入我们眼睛的复杂模式被用来恢复我们环境的三维结构。为了快速有效地做到这一点，我们的视觉系统做出了某些假设。例如，在没有其他信息的情况下，我们假设对象是从上方照明的(“来自上方的光”)。想象一下，一只鸡蛋坐在太阳下。底纹使鸡蛋的顶部明亮，底部更暗。在看不到光源的情况下，我们假设它在头顶上，并使用这个假设来帮助确定鸡蛋的形状，即凸起。相比之下，如果你举起一个打开的蛋盒，每个凹陷的顶部都会是暗的，底部会变得更亮，这有助于你看到它是凹陷的。来自上方的光线可以帮助我们根据物体的阴影模式来估计物体的形状：这个过程被称为从阴影到形状(SFS)。我们感兴趣的是，视觉假设(“先验”)是与生俱来的，还是在与环境的互动中习得的。鸡总是解读阴影图案，就好像光源在头顶上一样，即使在光线总是从下面出来的环境中饲养也是如此。相比之下，在光源总是偏向一侧的环境中接受训练的人类，会学习相应地解释物体。一系列实验将调查人类视觉系统的适应能力。观察者将通过一个“机械臂”观察和触摸虚拟物体，它允许我们操纵物体感觉是凸起还是凹陷。使用这种方法，我们将训练人们相信物体是从侧面或从下面照明的。我们将测量这种训练如何影响对其他新奇物体的解释，以及这种影响持续多久。因此，我们可以揭示人类视觉系统如何以及在什么时间尺度上适应其环境的变化。根据阴影图案的不同，很容易在许多凸起对象(例如按钮)中找到凹面对象(例如酒窝)。如果物体是从上面照亮的，那么这种凸凹式视觉搜索任务最容易完成，这与之前的“从上面照亮”是一致的。这提供了一种有用的方法来研究从上方照射的先验以及它如何与其他视觉场景信息相互作用。例如，关于“从上面来的光”是否会随着头部移动，证据是混杂的，如果你是颠倒的，你就会认为物体是从下面照亮的。我们可以通过让观察者用他们的头或身体在不同方向上执行视觉搜索任务来研究这一点。我们还可以问，SFS是否受到语境的影响。例如，如果周围的物体是从侧面清楚地照明的，那么视觉系统也可能会将中央对象解释为好像它们是从侧面照明的。当观察者主动移动光源时，视觉搜索性能也会发生变化。视觉搜索行为将与形状判断(凸面与凹面)以及对亮或暗物体外观的判断进行比较。所有这些任务都使用“自上而下”的方式，但可能会受到语境操纵的不同影响。例如，头部位置可能会影响形状判断，但不会影响视觉搜索。任务之间的差异将让我们了解涉及形状和阴影的各种判断背后的机制差异。这项工作与对视觉系统使用的假设感兴趣的科学家非常相关；很少有研究调查先验是如何获得的，它们有多普遍，以及它们如何受到上下文信息的影响。更广泛地说，任何使用远程呈现视觉或触摸信息(例如，虚拟现实、远程手术)的人都应该意识到观察者用来解释显示的假设。例如，显示方向和先前的经验可能会极大地影响3D感知，特别是在线索条件减弱的情况下。

The complex pattern of light entering our eyes as we view the world is used to recover the three-dimensional structure of our environment. To do this quickly and efficiently our visual system makes certain assumptions. For example, in the absence of other information, we assume that objects are illuminated from above ('light-from-above prior'). Imagine an egg sitting in the sun. Shading makes the egg bright on the top and darker underneath. Without seeing the light-source we assume that it is overhead and use this assumption to help determine the shape of the egg, i.e. convex. In contrast, if you held up an open egg-box, each depression would be dark at the top and brighter at the bottom, helping you to see it as concave. The 'light-from-above' prior helps us to estimate the shape of an object from its shading pattern: a process called 'shape-from-shading' (SFS). We are interested in whether visual assumptions ('priors') are innate or learnt in response to interactions with the environment. Chickens always interpret shading patterns as if the light source was overhead, even if raised in an environment where light always comes from below. In contrast, humans trained in an environment where the light-source is always to one side learn to interpret objects accordingly. A series of experiments will investigate just how adaptable the human visual system is. Observers will view and touch virtual objects via a 'robot arm' that allows us to manipulate whether the objects feel convex or concave. With this method we will train people to believe that objects are lit from the side or from below. We will measure how this training affects the interpretation of other, novel objects, and how long the effects last. We can thus uncover how and over what time-scale the human visual system adapts to changes in its environment.A concave object (e.g. dimple) is easy to find amongst many convex objects (e.g. buttons), based on differences in the shading patterns. This convex / concave visual search task is easiest if the objects are lit from above, consistent with the 'light-from-above' prior. This provides a useful method to investigate the 'light-from-above' prior and how it interacts with other visual scene information.The mechanisms for implementing the 'light-from-above' prior could be very simple or quite complex. For example, evidence is mixed on whether the 'light-from-above' prior moves with the head, such that if you were upside-down you would assume that objects were lit from below. We can investigate this by asking observers to perform visual search tasks with their head or body at different orientations. We can also ask whether SFS is affected by context. For example, if surrounding objects are clearly lit from the side, then the visual system might also interpret central objects as if they are lit from the side. Visual search performance may also change when observers actively move the light source.Visual search behaviour will be compared to shape judgements (convex vs. concave) and judgements about how light or dark objects appear. All of these tasks use the 'light-from-above' prior but may be differentially affected by contextual manipulations. For example, head position might affect shape judgements but not visual search. Differences between the tasks will inform us about the divergence of mechanisms behind various judgements involving shape and shading.This work is of great relevance to scientists interested in the assumptions that the visual system uses; little research has investigated how priors are learnt, how general they are and how they are affected by contextual information. More broadly, anyone using remote presentation of visual or touch information (e.g. virtual reality, remote surgery) should be aware of the assumptions that observers use to interpret displays. For example, display orientation and previous experience could dramatically affect 3D perception, especially under diminished cue conditions.