初级视皮层在运动错觉和大范围运动信息整合中的作用机制

It is the general consensus that the primary visual cortex (V1) is to process the directions of local motion components of a moving object, while the mechanisms responsible for processing the global direction of the object are thought to occur in the higher stages of the visual cortex. We observed a phenomenon of motion illusion in which as a large object is moving horizontally and a small object is superposed on the large one and is moving vertically, human subjects perceive that the small object contains the horizontal motion signal. In principle, the horizontal motion signal that the small object does not originally carry is induced by the horizontal motion of the large object. The motion illusion induced by the surround motion, to our knowledge, has not been reported before. We have explored the neural mechanisms underlying the novel illusion phenomenon by skillfully designing visual stimuli. The preliminary results showed that the selective activity of a portion of neurons in cat V1 to motion direction is correlated to this motion illusion. Since the motion signals of the large object only derived from its surround borders that are moving in the regions distanced far away from the small object, the results suggest that at the primary stage of the visual information processing, V1 cells represent the motion illusion induced by the surround motion and integrate motion information in a large visual field. We have also successfully trained monkeys to perform the behavioral tasks designed according to the surround motion-induced illusion. The measured psychometric functions illustrate that monkeys can perceive the motion illusion. By applying the psychophysical and electrophysiological methods, we intend to further investigate the psychophysics and the correlation between the perception for the surround motion-induced illusion and direction-selective activity of monkey V1 cells in order to understand the mechanisms underlying the motion illusion and the integration of the global direction from the component directions of local motion of a moving large object. It is important to understand the roles of V1 in motion illusion and global integration of motion information and to further elucidate the contribution of V1 to motion information processing because all previous studies believe that the higher visual cortex represents motion illusion and integrates motion signals over a large field and that V1 only represents local motion components. The study will provide the evidences for the roles of V1 in the high order visual functions, such as illusion.

普遍认为初级视皮层（V1）只处理局部运动信号，而物体整体运动信息的整合和运动错觉的机制发生在高级视皮层。我们观察到一种运动错觉现象。当一大物体在水平方向左右运动，一个小物体叠加其上并在垂直上下运动时，这个小物体也会被知觉到带有水平方向的运动信息。我们探讨了这一知觉现象的神经机制。初步结果提示猫V1部分细胞对运动方向的选择性活动与这一外周诱导的运动错觉相关，在感觉信息加工的初级阶段，V1细胞就整合了大范围的运动信息，并已表征了运动错觉。经训练,猕猴已能完成根据这一错觉现象设计的行为任务，测量的心理物理曲线说明猴也能知觉到这一运动错觉。在此基础上，我们计划研究感知这一运动错觉的心理物理性质，结合电生理技术分析猴V1细胞的方向选择性活动与这种错觉的相关性的性质和规律，研究V1在运动错觉和大范围运动信息整合中的作用，更全面地阐明V1处理运动信息的机制，为认识V1在高级视觉功能中的作用提供证据。

基于我们观察到一种外周运动诱导的运动错觉现象，我们精巧地设计了视觉刺激，采用单细胞电极记录方法，在麻醉家猫的初级视皮层（V1），记录到部分神经元对运动方向的选择性活动与这一外周运动诱导的运动错觉相关，提示在感觉信息加工的初级阶段，V1神经元就参与整合大范围的运动信息和表征运动错觉。我们试图在非人灵长类猕猴的V1深入研究这一运动错觉现象的神经机制，把V1神经元的活动直接与灵长类的知觉关联起来。在行为训练中测量的心理物理曲线揭示猕猴能感知这种由外周运动诱导的运动错觉现象。为了能够在清醒猕猴V1定量地研究神经元的活动与灵长类对这种运动错觉感知的相关性和机制，需要提高猕猴完成任务的成功率，即提高代表不同任务条件、反映认知能力的心理物理曲线的分辨率。当用更严格的实验参数设计的视觉任务来训练猕猴时，我们的分析提示猕猴可能采用了不是我们能够控制或希望的行为策略来完成对这种运动错觉任务的知觉报告，猕猴对运动错觉的知觉与报告结果的奖赏行为之间存在悖论。面对这样无解的困局，我们只能改变研究路线，在麻醉猕猴上研究V1神经元的活动与这种运动错觉的相关性和编码机制，已获得初步结果，研究仍在进行中。通过研究灵长类V1在运动错觉和大范围运动信息整合中的作用，能更全面地阐明V1处理运动信息的机制，为认识V1在高级视觉功能中的作用提供证据，因为传统观点认为V1只处理物体的局部运动信号，而物体整体运动信息的整合和负责运动错觉的机制发生在高级视皮层。另外，由于受到上述悖论的困扰，导致本项目进展滞后，为了弥补这样的不足，我们开展了早期视觉通路处理其它视觉信息机制的研究。在V1神经元编码对比度的时间特性，外膝体神经元处理亮度分布的机制，早期视觉通路的视网膜、外膝体和V1神经元加工快速变化的亮度和对比度信息的机制等方面取得了进展和结果，部分结果已发表或投稿，这些结果揭示了早期视觉通路信息处理的神经回路和机制，弥补了本项目研究进展滞后的不足。