Department of Precision Mechanics, Chuo University, Tokyo, Japan.
PLoS One. 2018 Oct 4;13(10):e0205099. doi: 10.1371/journal.pone.0205099. eCollection 2018.
In the human retina, rod and cone cells detect incoming light with a molecule called rhodopsin. After rhodopsin molecules are activated (by photon impact), these molecules activate the rest of the signalling process for a brief period of time until they are deactivated by a multistage process. First, active rhodopsin is phosphorylated multiple times. Following this, they are further inhibited by the binding of molecules called arrestins. Finally, they decay into opsins. The time required for each of these stages becomes progressively longer, and each stage further reduces the activity of rhodopsin. However, while this deactivation process itself is well researched, the roles of the above stages in signal (and image) processing are poorly understood. In this paper, we will show that the activity of rhodopsin molecules during the deactivation process can be described as the fractional integration of an incoming signal. Furthermore, we show how this affects an image; specifically, the effect of fractional integration in video and signal processing and how it reduces noise and the improves adaptability under different lighting conditions. Our experimental results provide a better understanding of vertebrate and human vision, and why the rods and cones of the retina differ from the light detectors in cameras.
在人类视网膜中，杆状细胞和锥状细胞通过一种叫做视紫红质的分子来检测入射光。视紫红质分子被激活（通过光子冲击）后，这些分子会在被多步过程失活之前短暂激活其余的信号传递过程。首先，活性视紫红质被多次磷酸化。之后，它们被称为阻滞蛋白的分子结合进一步抑制。最后，它们衰变成视蛋白。每个阶段所需的时间变得越来越长，每个阶段进一步降低视紫红质的活性。然而，尽管这个失活过程本身已经得到了很好的研究，但上述阶段在信号（和图像）处理中的作用还知之甚少。在本文中，我们将表明，在失活过程中视紫红质分子的活性可以被描述为输入信号的分数积分。此外，我们还展示了这如何影响图像；具体来说，分数积分在视频和信号处理中的影响，以及它如何在不同光照条件下降低噪声和提高适应性。我们的实验结果提供了对脊椎动物和人类视觉的更好理解，以及为什么视网膜中的杆状细胞和锥状细胞与相机中的光探测器不同。
