Chaparro A, Stromeyer C F, Chen G, Kronauer R E
Division of Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
Vision Res. 1995 Nov;35(22):3103-18. doi: 10.1016/0042-6989(95)00069-c.
Recent physiological evidence suggests that cones do not light adapt at low light levels. To assess whether adaptation is cone-selective at low light levels, the red-green detection mechanism was isolated. Thresholds were measured with a large test flash, which stimulated the L and M cones in different fixed amplitude ratios, on different colored adapting fields. Thresholds were plotted in L and M cone contrast coordinates. The red-green mechanism responded to an equally-weighted difference of L and M cone contrast on each colored field, demonstrating equivalent, Weberian adaptation of the L and M cone signals. The L and M cone signals independently adapted for illuminance levels as low as 60 effective trolands (e.g. M-cone trolands). Since this adaptation is entirely selective to cone type, it suggests that the cones themselves light-adapt. The red-green detection contour on reddish fields was displaced further out from the origin of the cone contrast coordinates, revealing an additional sensitivity loss at a subsequent, spectrally-opponent site. This second-site effect may arise from a net "red" or "green" signal that represents the degree to which the L and M cones are differently hyperpolarized by the steady, colored adapting field. Such differential hyperpolarization is compatible with equivalent, Weberian adaptation of the L and M cones.
最近的生理学证据表明，在低光照水平下视锥细胞不会进行光适应。为了评估在低光照水平下适应是否具有视锥细胞选择性，分离了红绿色检测机制。使用大的测试闪光测量阈值，该闪光以不同的固定幅度比刺激L和M视锥细胞，在不同颜色的适应场中进行。阈值以L和M视锥细胞对比度坐标绘制。红绿色机制对每个颜色场中L和M视锥细胞对比度的等权重差异做出反应，表明L和M视锥细胞信号具有等效的韦伯式适应。L和M视锥细胞信号在低至60有效托兰（例如M视锥细胞托兰）的照度水平下独立适应。由于这种适应完全对视锥细胞类型具有选择性，这表明视锥细胞本身会进行光适应。在微红场地上的红绿色检测轮廓从视锥细胞对比度坐标的原点进一步向外偏移，揭示了在随后的光谱对立位点处额外的灵敏度损失。这种第二位点效应可能源于代表L和M视锥细胞被稳定的彩色适应场不同程度超极化的净“红色”或“绿色”信号。这种差异超极化与L和M视锥细胞的等效韦伯式适应是兼容的。
