Naka K I, Itoh M A, Chappell R L
J Gen Physiol. 1987 Feb;89(2):321-37. doi: 10.1085/jgp.89.2.321.
The response dynamics of turtle photoreceptors (cones) were studied by the cross-correlation method using a white-noise-modulated light stimulus. Incremental responses were characterized by the kernels. White-noise-evoked responses with a peak-to-peak excursion of greater than 5 mV were linear, with mean square errors of approximately 8%, a degree of linearity comparable to the horizontal cell responses. Both a spot (0.17 mm diam) and a large field of light produced almost identical kernels. The amplitudes of receptor kernels obtained at various mean irradiances fitted approximately the Weber-Fechner relationship and the mean levels controlled both the amplitude and the response dynamics; kernels were slow and monophasic at low mean irradiance and were fast and biphasic at high mean irradiance. This is a parametric change and is a piecewise linearization. Horizontal cell kernels evoked by the small spot of light were monophasic and slower than the receptor kernels produced by the same stimulus. Larger spots of light or a steady annular illumination transformed the slow horizontal cell kernel into a fast kernel similar to those of the receptors. The slowing down of the kernel waveform was modeled by a simple low-pass circuit and the presumed feedback from horizontal cells onto cones did not appear to play a major role.
采用白噪声调制光刺激的互相关方法，研究了龟类光感受器（视锥细胞）的反应动力学。增量反应以核函数来表征。峰峰值偏移大于5 mV的白噪声诱发反应呈线性，均方误差约为8%，线性程度与水平细胞反应相当。一个光斑（直径0.17 mm）和一个大的光场产生的核函数几乎相同。在不同平均辐照度下获得的感受器核函数的振幅大致符合韦伯-费希纳关系，平均水平同时控制振幅和反应动力学；在低平均辐照度下，核函数缓慢且单相，在高平均辐照度下则快速且双相。这是一种参数变化，是一种分段线性化。由小光斑光诱发的水平细胞核函数是单相的，且比相同刺激产生的感受器核函数慢。较大的光斑或稳定的环形照明将缓慢的水平细胞核函数转变为类似于感受器的快速核函数。核函数波形的减慢由一个简单的低通电路建模，并且水平细胞向视锥细胞的假定反馈似乎并未起主要作用。
