Data from: Mechanism for analogous illusory motion perception in flies and humans.

Visual motion detection is one of the most important computations performed by visual circuits. Yet, we perceive vivid illusory motion in stationary, periodic luminance gradients that contain no true motion. This illusion is shared by diverse vertebrate species, but theories proposed to explain this illusion have remained difficult to test. Here, we demonstrate that in the fruit fly Drosophila, the illusory motion percept is generated by unbalanced contributions of direction-selective neurons’ responses to stationary edges. First, we found that flies, like humans, perceive sustained motion in the stationary gradients. The percept was abolished when the elementary motion detector neurons, T4 and T5, were silenced. In vivo calcium imaging revealed that T4 and T5 neurons encode the location and polarity of stationary edges. Furthermore, our proposed mechanistic model allowed us to predictably manipulate both the magnitude and direction of the fly’s illusory percept by selectively silencing either T4 or T5 neurons. Interestingly, human brains possess the same mechanistic ingredients that drive our model in flies. When we adapted human observers to moving light edges or dark edges, we could manipulate the magnitude and direction of their percepts as well, suggesting that mechanisms similar to the fly’s may also underlie this illusion in humans. By taking a comparative approach that exploits Drosophila neurogenetics, our results provide a causal, mechanistic account for a long-known visual illusion. These results argue that this illusion arises from architectures for motion detection that are shared across phyla.

视觉运动检测是视觉神经环路所执行的最为关键的计算任务之一。然而，我们会在不含真实运动的静态周期性亮度梯度中感知到生动的错觉运动。这类视觉错觉在多种脊椎动物中均存在，但目前用以解释该错觉的理论始终难以得到验证。本研究以黑腹果蝇（Drosophila）为模型，证实这类错觉运动感知源于方向选择性神经元对静态边缘的响应贡献失衡。首先，研究团队发现果蝇与人类一样，会在静态亮度梯度中感知到持续性运动；当初级运动检测神经元T4与T5被沉默后，该感知会被完全消除。体内钙成像实验结果显示，T4与T5神经元能够编码静态边缘的位置与极性信息。此外，我们提出的机制模型可通过选择性沉默T4或T5神经元，可控地调控果蝇错觉感知的强度与方向。值得注意的是，人类大脑同样具备驱动果蝇模型的同类机制组分：当我们让人类受试者适应运动的亮边缘或暗边缘后，同样可以调控其感知的强度与方向，这表明人类的这类视觉错觉可能同样由与果蝇相似的机制所介导。本研究借助利用黑腹果蝇神经遗传学的比较研究方法，为这一长期被观测到的视觉错觉提供了因果性的机制解释。上述结果表明，这类错觉源于跨动物门共享的运动检测神经环路架构。