朝向和对比度同时快速变化条件下的分辨能力

在自然的视觉中，投射到视网膜上的视觉图像总是在不停地变化，而人类的感知系统依然可以准确高效地识别物体.因此，人类的感知系统有相应的快速处理机制以应对这种动态变化．然而，前人的实验都是在相对稳定的刺激条件下研究人类被试的感知系统对一个刺激参数的反应，比如在固定对比度下测试朝向分辨能力，或在固定朝向测定对比度分辨能力，而朝向和对比度同时变化时，人类对这两个参数的分辨能力仍然缺乏研究．因此，在本实验中，我们使用朝向和对比度同时变化的刺激,研究了人类被试对朝向和对比度的分辨能力．结果表明，在这种动态变化的条件下，被试对朝向和对比度的分辨阈值都有显著性的降低．而且，朝向分辨阈值降低的幅度与在固定对比度参数条件下的分辨阈值成负相关，即在固定对比度条件下朝向分辨阈值较高的被试，在朝向和对比度同时变化条件下，其朝向分辨阈值降低的幅度相对要大，朝向分辨能力也就相对地提高更大．对比度分辨能力也呈现同样的规律．这些结果说明，朝向和对比度的同时变化提高了被试对朝向和对比度的分辨能力，一个参数变化时其分辨能力越低的被试，两个参数变化时其分辨能力提高的幅度就越大．揭示了视觉系统处理这种多刺激参量信息变化的能力和机制，对人类视觉系统在真实的视觉过程中如何处理朝向和对比度信息提供了认识．

Contrast and Orientation Discrimination in Simultaneous Orientation and Contrast Changes

In natural vision, due to object, body, head, and eye movements, the contrast and orientation information received by our eyes change simultaneously and rapidly, yet our visual system can efficiently and accurately distinguish the contrasts and orientations under the dynamical conditions. The visual processes responsible for discriminating orientations and contrasts occurred at this very short time scale, however, are poorly understood. In the current experiments, we investigated the ability of human subjects to discriminate orientations or contrasts using the briefly presented stimuli in which orientations and contrasts were changing simultaneously in comparison with the stimuli in which orientation changes were discriminated when contrast remained constant or contrast changes were discriminated when orientation was constant. We show that the discrimination threshold for orientation or contrast when both contrast and orientation were varying was significantly lower than that for orientation when contrast was fixed or than that for contrast when orientation was fixed. Moreover, the decreased magnitude of discrimination thresholds to orientation or contrast was negatively correlated to the discrimination threshold to orientation or contrast when only orientation or only contrast was varied. These results indicate that the simultaneous changes in orientation and contrast enhanced the discriminability of subjects to contrast and orientation. The subjects who had lower discriminability to orientation or contrast when only orientation or contrast was changing had a relatively larger enhancement in their ability to discriminate contrasts and orientations when both orientation and contrast were changing simultaneously. We suggest that human visual system is more efficient at discriminating orientation and contrast when both parameters are changing which often occurs in natural environments. Our study sheds light on the underlying visual processes.