北京师范大学认知神经科学与学习国家重点实验室李武老师及其博士生张恩二人在PNAS杂志上发表重要学术文章。李武老师及其博士生张恩二人在2010年9月7日出版的PNAS杂志上发表了重要学术文章。
视觉信息的加工在很大程度上依赖于视网膜坐标系，可是在表征外界刺激的空间位置时，视觉系统需要独立于视网膜坐标的编码机制，这对于多种感觉信息的整合以及感觉-运动整合至关重要；此外，眼动和头动会导致图像在视网膜上变动，而非网膜坐标系下的加工机制可以确保视知觉的稳定。因而，视觉信息的非网膜坐标表征一直是视觉研究的热点。但是，目前还没有研究者探讨过非网膜坐标下的视觉表征是否具有经验依赖性。然而，人的视觉检测和分辨能力会随着训练而逐渐提高。这种知觉学习现象通常特异于训练过的视网膜（或视野）位置，也即，学习的效果不能从训练过的位置迁移到没有训练过的位置。但是，传统的知觉学习研究往往是在眼睛注视方向不变的情况下进行，不能区分知觉学习是单纯视网膜位置特异的，还是依赖于刺激的非网膜位置。
李武与其合作者的最新研究通过巧妙的实验设计，独立改变刺激的视网膜和空间位置，探讨了知觉学习位置特异性的参考坐标系。研究发现，除网膜特异性之外，知觉学习也是空间坐标特异的，依赖于训练刺激在空间坐标系下的相对位置，但并不受限于刺激的绝对空间位置。这一发现表明，训练不仅能改变基于视网膜坐标的编码机制，而且能特异地改变基于非网膜坐标的信息加工。
这一研究大大加深了人类对知觉学习、视觉系统的可塑性、以及非网膜坐标系下动态视觉信息加工的理解和认识。
推荐英文摘要：
PNAS doi: 10.1073/pnas.1003547107
Perceptual learning beyond retinotopic reference frame
En Zhang and Wu Li1
Repetitive experience with the same visual stimulus and task can remarkably improve behavioral performance on the task. This well-known perceptual-learning phenomenon is usually specific to the trained retinal- or visual-field location, which is taken as an indication of plastic changes in retinotopic visual areas. In previous studies of perceptual learning, however, a change in stimulus location on the retina is accompanied by positional changes of the stimulus in nonretinotopic frames of reference, such as relative to the head and other objects. It is unclear, therefore, whether the putative location specificity is exclusively retinotopic or if it could also depend on nonretinotopic representation of the stimulus, which is particularly important for multisensory and sensorimotor integration as well as for maintenance of stable visual percepts. Here, by manipulating subjects’ gaze direction to control spatial and retinal locations of stimuli independently, we found that, when the stimulated retinal regions were held constant, the improvement with training in motion-direction discrimination of two successively displayed stimuli was restricted to the relative spatial position of the stimuli but independent of their absolute locations in head- and world-centered frame. These findings indicate location specificity of perceptual learning beyond retinotopic frame of reference, suggesting a pliable spatiotopic mechanism that can be specifically shaped by experience for better spatiotemporal integration of the learned stimuli.
