Zaghloul Kareem A, Boahen Kwabena
Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA 19104, USA.
IEEE Trans Biomed Eng. 2004 Apr;51(4):657-66. doi: 10.1109/tbme.2003.821039.
We present a novel model for the mammalian retina and analyze its behavior. Our outer retina model performs bandpass spatiotemporal filtering. It is comprised of two reciprocally connected resistive grids that model the cone and horizontal cell syncytia. We show analytically that its sensitivity is proportional to the space-constant-ratio of the two grids while its half-max response is set by the local average intensity. Thus, this outer retina model realizes luminance adaptation. Our inner retina model performs high-pass temporal filtering. It features slow negative feedback whose strength is modulated by a locally computed measure of temporal contrast, modeling two kinds of amacrine cells, one narrow-field, the other wide-field. We show analytically that, when the input is spectrally pure, the corner-frequency tracks the input frequency. But when the input is broadband, the corner frequency is proportional to contrast. Thus, this inner retina model realizes temporal frequency adaptation as well as contrast gain control. We present CMOS circuit designs for our retina model in this paper as well. Experimental measurements from the fabricated chip, and validation of our analytical results, are presented in the companion paper [Zaghloul and Boahen (2004)].
我们提出了一种新型的哺乳动物视网膜模型并分析了其行为。我们的外层视网膜模型执行带通时空滤波。它由两个相互连接的电阻性网格组成，这两个网格对视锥细胞和水平细胞合体进行建模。我们通过分析表明，其灵敏度与两个网格的空间常数比成正比，而其半最大值响应由局部平均强度设定。因此，这个外层视网膜模型实现了亮度适应。我们的内层视网膜模型执行高通时间滤波。它具有缓慢的负反馈，其强度由局部计算的时间对比度测量值调制，对两种无长突细胞进行建模，一种是窄场的，另一种是宽场的。我们通过分析表明，当输入是光谱纯时，截止频率跟踪输入频率。但当输入是宽带时，截止频率与对比度成正比。因此，这个内层视网膜模型实现了时间频率适应以及对比度增益控制。在本文中我们还展示了用于我们视网膜模型的CMOS电路设计。来自制造芯片的实验测量结果以及对我们分析结果的验证在配套论文[扎格卢勒和博阿亨（2004年）]中给出。
