Sharpe L T, Fach C C, Stockman A
Neurologische Universitätsklinik, Freiburg, Germany.
Vision Res. 1993 Dec;33(18):2705-20. doi: 10.1016/0042-6989(93)90230-t.
Psychophysical and electroretinographic observations in normal and achromat observers suggest that rod flicker signals have access to at least two retinal pathways: one (pi 0), slow and sensitive, predominating at scotopic luminance levels; the other (pi'0), fast and insensitive, predominating at mesopic ones. We have measured steady-state flicker detection sensitivities on background fields ranging from 430 to 640 nm in normal observers. Our results suggest that cone signals can reduce the sensitivity of pi'0, but have comparatively little effect on pi 0. The pi'0 field sensitivities derived from these measurements have been fitted with linear combinations of the scotopic luminosity function, V' lambda, the M-cone spectral sensitivity function, M lambda, and the L-cone function, L lambda. These fits demonstrate a clear cone influence on pi'0, but they cannot tell us unequivocally whether the influence is from the M-cones, from the L-cones or from both. Accordingly, we made similar measurements in dichromats, who lack one of the two longer wavelength cone types. These measurements revealed an L-cone influence on pi'0 in the deuteranope and an M-cone influence in the protanope. This suggests that both cone types can affect the sensitivity of pi'0. The finding that the steady-state cone signals reduce the sensitivity of pi'0 but have little effect on pi 0 could suggest that pi'0 signals travel through a faster cone pathway (with its own gain control at which both rod and cone signals can reduce rod threshold), while pi 0 signals travel through a separate rod pathway. However, it could simply reflect the fact that pi'0 predominates at higher luminances than pi 0 where the cone excitation level is inevitably greater. To examine the influence of the cones on pi 0 more closely, we: (i) produced transient cone excitation by alternating rod-equated 480 and 679 nm fields; and (ii) extended our steady-state measurements to include deep-red backgrounds of 650 and 680 nm. Both experiments revealed a small, but measurable influence of the cones on pi 0.
对正常观察者和色盲观察者进行的心理物理学和视网膜电图观察表明，视杆细胞闪烁信号至少可通过两条视网膜通路：一条（π0），缓慢且敏感，在暗视亮度水平占主导；另一条（π'0），快速且不敏感，在中间视觉亮度水平占主导。我们测量了正常观察者在430至640纳米背景光场上的稳态闪烁检测敏感度。我们的结果表明，视锥细胞信号可降低π'0的敏感度，但对π0的影响相对较小。从这些测量中得出的π'0场敏感度已通过暗视光度函数V'λ、M视锥细胞光谱敏感度函数Mλ和L视锥细胞函数Lλ的线性组合进行拟合。这些拟合结果表明视锥细胞对π'0有明显影响，但无法明确告诉我们这种影响是来自M视锥细胞、L视锥细胞还是两者皆有。因此，我们在缺乏两种较长波长视锥细胞类型之一的二色视者中进行了类似测量。这些测量结果显示，在绿色盲患者中L视锥细胞对π'0有影响，而在红色盲患者中M视锥细胞对π'0有影响。这表明两种视锥细胞类型均可影响π'0的敏感度。稳态视锥细胞信号降低π'0敏感度但对π0影响较小这一发现可能表明，π'0信号通过一条更快的视锥细胞通路（有其自身的增益控制，视杆细胞和视锥细胞信号均可在此降低视杆细胞阈值）传播，而π0信号通过一条独立的视杆细胞通路传播。然而，这可能仅仅反映了这样一个事实，即π'0在比π0更高的亮度下占主导，而在更高亮度下视锥细胞的激发水平必然更高。为了更仔细地研究视锥细胞对π0的影响，我们：（i）通过交替使用与视杆细胞等效的480和679纳米场产生瞬态视锥细胞激发；（ii）将我们的稳态测量扩展到包括650和680纳米的深红色背景。两个实验均显示视锥细胞对π0有微小但可测量的影响。
