Perceptual Learning in Motion Processing

视觉感知被认为是一种被动而简单的事件。这一观点可能建立在这样的假设之上，即视觉信息只能单向地从视网膜传到大脑的高级区域。沿着这个方向流动的处理称为“自下而上的处理”。然而，最近的解剖学和生理学发现表明，大脑中有大量的反馈路径，沿着这些路径，信息从这些较高级别的大脑区域返回到低级别区域，包括那些参与处理视觉信息的区域。沿着这些途径进行的处理称为“自上而下的处理”。不幸的是，自上而下的加工在大脑的视觉信息处理中扮演了什么角色，目前还知之甚少。与此同时，最近的生理学研究指出，即使是成年人大脑中处理原始视觉信息的部分，其可塑性也比之前认为的要高得多。这种可塑性的行为表现是，非常原始的视觉功能，如对运动方向和线条方向的辨别，可以因为重复的试验而得到改善。因此，一个有趣的问题出现了。在运动加工的早期阶段，自上而下的加工会影响知觉学习吗？如果是，自上而下处理的作用是什么？这项研究将考察自上而下加工的性质和作用，以及它在知觉学习过程中与自下而上加工的相互作用。将使用几个人体受试者进行一系列实验。他们将观看一种被称为随机点电影的刺激，它由在一定方向范围内随机移动的小点组成。在每个刺激中，全球流动被认为是朝着一个方向移动，就像河流的流动一样。这表明在早期的运动加工中至少存在两个阶段：第一个局部运动阶段和第二个全局运动阶段。我们将首先检查来自全局运动处理阶段的自上而下信号对较低阶段的影响程度。初步实验结果表明，在学习全局运动的过程中，较低的阶段可能会受到自上而下信号的强烈影响。我们将进行实验，以更系统地检验这一点。其次，我们将考察自上而下和自下而上加工之间的交互作用在知觉学习中的作用。对于我们的实验来说，基本的是一种“自下而上不存在”的随机点电影图像，它不包括在接近全局运动方向的方向上移动的任何点，使得预期的全局运动方向的激活不能归因于自下而上的信号。使用这种自下而上的无刺激，我们将检查位置特异性以及学习过程中涉及的阶段，并将结果与使用传统的“自下而上-呈现”刺激的结果进行比较。这两种类型的刺激结果的不同表明自下而上的激活以及自下而上和自上而下的加工之间的交互作用。

Visual perception is thought of as a passive and simple event. This view may stand on the assumption that visual information goes from the retina to higher-level areas in the brain only in a one-way direction. Processing that flows in this direction is called "bottom-up processing." However, recent anatomical and physiological findings indicate that there are massive feedback pathways in the brain along which information is carried from these higher-level brain areas back to low-level areas, including those involved in processing visual information. Processing that occurs along these pathways is called "top-down processing." Unfortunately, it is poorly known what role top-down processing play in visual information processing in the brain. In the meantime, recent physiological studies have pointed out that even the parts of the adult brain which process primitive visual information have much higher plasticity than had been previously thought. The behavioral manifestation of this plasticity is that very primitive visual functions such as discrimination of motion direction and orientation of lines can be improved as a result of repetitive trials. Thus, an interesting question arises. Does top-down processing influence perceptual learning in the early stages of motion processing? If so, what is the role of top-down processing? The proposed study will examine the nature and role of top-down processing and its interaction with bottom-up processing during perceptual learning. A series of experiments will be conducted using several human subjects. They will watch a stimulus called random-dot cinematogram which consists of small dots moving randomly within a certain range of directions. In each stimulus, a global flow is perceived to move in one direction just like a flow of a river. This indicates that there are at least two stages in early motion processing; the first, local motion stage and the second, global motion stages. We will first examine the extent to which top-down signals from the stage of global motion processing affect lower stages. The results of preliminary experiments suggest that during the learning of global motion lower stages may be strongly affected by top-down signals. We will conduct experiments to examine this more systematically. Second, we will examine the role of the interaction between top-down and bottom-up processing in perceptual learning. Essential to our experiments is a "bottom-up-absent" random-dot cinematogram which does not include any dots moving in directions close to the global motion direction such that activation of the intended global motion direction can not be attributed to bottom-up signals. Using this bottom-up-absent stimulus, we will examine location specificity as well as the stages involved in learning and compare the results with those using the conventional "bottom-up-present" stimulus. A difference in results between the two types of stimuli would suggest roles for bottom-up activation and the interaction between bottom-up and top-down processing.