An psychophysical and computational study on the mechanism of early vision with respect to the phenomenon of perceptual filling-in/fading

本项目旨在通过对“知觉填充”或“知觉消退”错觉现象的心理物理和计算研究，了解早期视觉包括表面补全和感知的机制。项目主要成果如下：首先，研究者建立了一个新的心理物理实验环境，在这个环境中，视觉刺激可以在一个大的视野范围内独立地呈现给两只眼睛，并开发了能够高效执行实验的计算机软件。利用这一系统，研究者系统地进行了一系列心理物理实验，研究了各种刺激参数（或视觉特征）如何影响感知填充/消退。他们的主要成果可以概括为以下几点：感知填充所需的时间取决于在视野中的位置。总的来说，当目标以水平方向呈现时，时间会比以垂直方向呈现时延长。当对目标区域和周围区域施加光栅时，视觉刺激的对比度对填充时间有显著影响。在一定的刺激条件下，两个不同区域的知觉衰退可能以同步的方式发生，表明两个不同区域的神经活动可能相互作用。当在目标附近放置一个额外的刺激（侧标）时，目标在侧标消失后立即消失（相反，当侧标出现在目标附近时，很少感觉到褪色）。这种衰减效应比传统的要显著得多：即使目标具有较高的对比度，并且位于较低的偏心率，它也能被感知到。除了这些心理检查，研究者和同事建立了一个表面完成和感知的神经网络模型。该模型由多个神经单元组成，每个神经单元代表3D对象的局部元素（或特征）的方向。这些单元之间相互作用形成的动力系统带来了物体的全局表面表征。计算机模拟结果表明，该神经模型的行为与人类对虚幻表面的感知相吻合。综上所述，本项目提供了新的发现，表明早期视觉的感知动态与特征表征紧密耦合。少

The present research project aims to understand the mechanism of early vision including surface completion and perception, by means of psychophysical and computational studies on an illusory phenomenon called "perceptual filling-in" or "perceptual fading". Major results of the project are as follows.First, the investigator built a new environment for psychophysical experiment, where visual stimuli can be presented over a large visual field and independently to both eyes, and developed computer software enabling efficient experimental execution. Utilizing this system, the investigator systematically ran a number of psychophysical experiments and examined how various stimulus parameters (or visual features) affected the perceptual filling-in/fading. Their principal results can be summarized in the following points :1.The time required for perceptual filling-in depended on the position in the visual field. In general, the time was prolonged when the target was presented in the horizontal … More direction than when it was presented in the vertical direction.2.The time for filling-in was significantly affected by the contrast of the visual stimuli when grating patterns were given to the target and surrounding regions.3.Perceptual fading could occur in a synchronized manner at two distinct regions under certain stimulus conditions, suggesting that the neural activities for two distinct areas might interact with each other.4.When an additional stimulus (flanker) was placed near the target, the target faded immediately after the flanker disappeared (In contrast, fading was rarely perceived when the flanker appeared near the target). This fading effect was much more remarkable than the conventional one: It was perceived even when the target had a higher contrast and was located at a lower eccentricity.In addition to these psychological examinations, the investigator and co-worker built a neural network model for surface completion and perception. This model consists of a number of neural units, each which represents the orientation of local element (or feature) of a 3D object. The dynamical system formed by interaction among these units brings global surface representation of the object. The result of computer simulation showed that the behavior of the neural model well corresponded to human perception of illusory surfaces.In conclusion, the present project has provided new findings suggesting that the perceptual dynamics is tightly coupled with the feature representation in early vision. Less