Reeves A, Wu S, Schirillo J
Department of Psychology, Northeastern University, Boston, MA 02115, USA.
Vision Res. 1998 Mar;38(5):691-703. doi: 10.1016/s0042-6989(97)00201-0.
Thresholds for detecting brief, white, foveal test flashes drop abruptly within 0.2 sec of the offset of a white adapting field. The magnitude of the abrupt drop is proportional to the square root of field intensity (square root of I) correct for bleaching and dark light. Thresholds are then stable out to 1.6 sec for 200 msec tests, or recover only slightly for 20 msec tests. These results exclude some simple deterministic models in which Weber-like gain controls in the luminance pathway are assumed to recover exponentially in the dark, but can be explained parsimoniously if turning off the field abolishes photon-driven noise, improving the S/N ratio while leaving visual responsivity virtually unaltered. This theory was first put forward by Krauskopf and Reeves [(1980) Vision Research, 20, 193-196] for S-cone thresholds; it implies that the Weber law for increment thresholds is not due to a single gain control, but rather expresses the product of two distinct square root of I factors, adjustment of responsivity and photon-driven noise. Removal of the noise, not recovery of gain, permits thresholds to fall in early dark adaptation.
检测短暂、白色、中央凹测试闪光的阈值在白色适应场消失后的0.2秒内会突然下降。突然下降的幅度与场强的平方根（I的平方根）成正比，这是针对漂白和暗光进行校正后的结果。对于200毫秒的测试，阈值在1.6秒内保持稳定；对于20毫秒的测试，阈值仅略有恢复。这些结果排除了一些简单的确定性模型，在这些模型中，假定亮度通路中类似韦伯定律的增益控制在黑暗中呈指数恢复，但如果关闭适应场能消除光子驱动的噪声，提高信噪比，同时视觉响应性几乎不变，那么这些结果就能得到简洁的解释。这一理论最早由克劳斯科普夫和里夫斯[（1980年）《视觉研究》，20卷，193 - 196页]针对S视锥细胞阈值提出；这意味着增量阈值的韦伯定律并非源于单一的增益控制，而是两个不同的I的平方根因子的乘积，即响应性调整和光子驱动噪声的结果。消除噪声而非恢复增益，使得阈值在早期暗适应中下降。
