Lưu ý rằng cả hai trung tâm và khu vực bao quanh đảo ngược dấu hiệu như một chức năng của τ và sự phát triển thời gian là chậm bao quanh hơn so với trung tâm. D) phù hợp với lĩnh vực tiếp nhận không gian-thời gian trong C bằng cách sử dụng 2,46 với các thông số tương tự cho các chức năng Gaussian như trong B, và thời gian | Receptive Fields in the Retina and LGN 35 A B 3 0 X degrees 3 0 Ds x degrees 0 -2 Figure Receptive fields of LGN neurons. A The center-surround spatial structure of the receptive field of a cat LGN X cell. This has a central ON region solid contours and a surrounding OFF region dashed contours . B A fit of the receptive field shown in A using a difference of Gaussian function equation with ơcen ơsur and B 5. C The space-time receptive field of a cat LGN X cell. Note that both the center and surround regions reverse sign as a function of T and that the temporal evolution is slower for the surround than for the center. D A fit of the space-time receptive field in C using with the same parameters for the Gaussian functions as in B and temporal factors given by equation with 1 acen 16 ms for the center 1 asur 32 ms for the surround and 1 cen 1 sur 64 ms. A and C adapted from DeAngelis et al. 1995. The sign allows both ON-center and OFF-center cases to be represented. Figure shows a spatial receptive field formed from the difference of two Gaussians that approximates the receptive field structure in figure . Figure shows that the spatial structure of the receptive field reverses over time with in this case a central ON region reversing to an OFF region as T increases. Similarly the OFF surround region changes to an ON region with increasing T although the reversal and the onset are slower for the surround than for the central region. Because of the difference between the time course of the center and surround regions the space-time receptive field is not separable although the center and surround components Draft December 17 2000 Theoretical Neuroscience 36 Neural Encoding II Reverse Correlation and Visual Receptive Fields are individually separable. The basic features of LGN neuron space-time receptive fields are captured by the mathematical caricature D x y T D. n M x2 y2 -. - xf - BDtsur r 2n 2ur exl - x2 y2 AA 2 2ur J
