Changes in visual computations across the visual field: depth and crowding

我们视野的中心(中心凹)具有最高的分辨细微细节的能力(敏锐度)，如果我们注意到周围有感兴趣的东西，我们会移动眼睛，使物体的图像落在中心凹，而不是视网膜的外围部分。我们这样做是因为我们的视觉系统在远离中心凹的地方视力不佳。通常令人惊讶的是，当一页上的字母与中心凹的距离(偏心率)增加时，我们能够识别出的字母是如此之少。 多年来，视觉科学家一直在研究周边视觉，并证实随着刺激的出现，视力会随着偏心程度的增加而下降。这可以通过让观察者盯着电脑显示器上的某个点，然后在外围闪烁刺激信号来实现，这样他们就没有时间移动眼睛直视它。然而，人们已经发现，在许多情况下，当外围呈现的刺激足够大时(相对于中心凹标准放大)，观察者可以像对呈现给中心凹的标准刺激一样准确地判断放大的刺激。 多年来，这类实验中使用的刺激一直是简单的几何形式(线条和字母)，很少有人注意到刺激放大是否可以让我们检测物体的三维形状、人走的方向，甚至步行者的身份。这里提出的研究的很大一部分正是针对这类问题。具体地说，我们询问刺激放大是否允许我们对周边的3D形状做出与我们在中心凹所能做出的判断一样准确的判断。我们询问这种能力对于孤立在视野中的刺激，或者被不同距离的侧翼物品包围的刺激，因为众所周知，在拥挤的背景中识别刺激在外围要比在注视下困难得多。虽然我们的兴趣是理论上的，但从长远来看，更好地了解周边视力的能力将使我们处于更有利的地位，帮助那些因黄斑变性等疾病而失去中心凹视力的人。

The centre of our visual field (the fovea) has the highest ability to resolve fine details (acuity), and if we notice something of interest in our surroundings we will move our eyes so that the image of the object falls on the fovea, rather than some peripheral part of our retinas. We do this because our visual systems have low acuity away from the fovea. If is often surprising how few letters on a page we are able to identify as their distance from the fovea (eccentricity) increases. For many years vision scientists have studied peripheral vision and verified that visual acuity falls off as stimuli are presented at increasing eccentricities. This can be done by having observers fixate at a point on computer monitor, and then flashing a stimulus in the periphery so that they don't have time to move their eyes to look directly at it. It has been found, however, that in many cases, when peripherally presented stimuli are made sufficiently large (magnified relative to a foveal standard), observers can be as accurate at making judgments about the magnified stimuli as they are about the standard stimuli presented to the fovea. For many years the stimuli used in experiments of this sort have been simple geometric forms (lines and letters) and little attention has been paid to whether stimulus magnification allows us to detect small differences the the three-dimensional shapes of objects, the direction that person is walking or even the identity of walkers. A large portion of the research proposed here deals with exactly this kind of question. Specifically, we asked whether stimulus magnification permits us to make judgements about 3D shapes in the periphery that are as accurate as those we can make at the fovea. We ask about this ability both for stimuli isolated in the visual field, or surrounded by flanking items at varying distances, because it is well know that identifying stimuli in a crowded background is much harder in the periphery than at fixation. Although our interests are theoretical, in the long run a better understanding of the abilities of peripheral vision will put us in a better position to help those who have lost foveal vision because of diseases like macular degeneration.