Perceptual Learning in Motion Processing

视觉感知被认为是一个被动和简单的事件。这种观点可能是基于视觉信息从视网膜到大脑高级区域的单向传递的假设。朝这个方向流动的处理称为“自底向上处理”。然而，最近的解剖学和生理学研究结果表明，大脑中存在大量的反馈通路，信息沿着这些高水平的大脑区域被传递回低水平的大脑区域，包括处理视觉信息的区域。沿着这些路径发生的处理被称为“自上而下的处理”。不幸的是，人们对自上而下的处理在大脑视觉信息处理中所起的作用知之甚少。与此同时，最近的生理学研究指出，即使是成人大脑中处理原始视觉信息的部分也比以前认为的具有更高的可塑性。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，可以通过反复试验而得到改善。因此，出现了一个有趣的问题。自上而下加工是否影响运动加工早期阶段的知觉学习？如果是这样，自上而下的处理是什么角色？本研究将探讨知觉学习过程中自上而下加工的性质和作用及其与自下而上加工的相互作用。一系列的实验将在几个人身上进行。他们将观看一种被称为随机点电影的刺激，它由在一定范围内随机移动的小点组成。在每一个刺激中，一个整体的流动被认为是向一个方向移动，就像河流的流动一样。这表明早期动作处理至少有两个阶段；第一个是局部运动阶段，第二个是全局运动阶段。我们将首先检查从全局运动处理阶段自上而下的信号影响较低阶段的程度。初步实验结果表明，在全局运动学习过程中，较低阶段可能受到自上而下信号的强烈影响。我们将进行实验，更系统地对此进行检验。其次，我们将研究自上而下和自下而上加工之间的相互作用在感知学习中的作用。我们实验的关键是一个“自下而上缺席”的随机点电影图，它不包括任何在接近全局运动方向的方向上移动的点，这样预期的全局运动方向的激活就不能归因于自下而上的信号。使用这种自下而上的缺席刺激，我们将检查位置特异性以及涉及学习的阶段，并将结果与使用传统的“自下而上的在场”刺激的结果进行比较。两种刺激结果的差异表明自下而上的激活作用以及自下而上和自上而下加工之间的相互作用。

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.