Alexander K R, Kelly S A, Morris M A
Vision Res. 1986;26(2):299-312. doi: 10.1016/0042-6989(86)90027-1.
To determine the effect of background size on saturation of the human rod system, we measured threshold-vs-intensity (tvi) functions for a 24'-diameter, middle-wavelength test stimulus against long-wavelength background fields that were either 2 degrees or 8 degrees in diameter. When thresholds were measured against a series of background intensities presented during a single experimental session (a standard tvi procedure), rod increment thresholds were higher against the smaller background and eventually disappeared above cone increment thresholds at moderate background intensities. This result suggests that background diameter does influence rod system saturation. However, when adaptation to the smaller background was limited to a 5 min exposure to a single background intensity per experimental session, then thresholds against that background were rod- rather than cone-mediated and were comparable to rod thresholds against an 8 degrees background. Therefore, under these stimulus conditions, background size apparently does not influence rod system saturation unless adaptation to the smaller background is prolonged. Based on previous studies, we suggest that the rod-desensitizing effect of small backgrounds under conditions of prolonged adaptation is due to a post-retinal mechanism.
为了确定背景大小对人眼视杆系统饱和度的影响，我们针对直径为2度或8度的长波长背景场，测量了直径24分视角的中波长测试刺激的阈值与强度（tvi）函数。当在单个实验环节中针对一系列呈现的背景强度测量阈值时（标准tvi程序），相对于较小的背景，视杆细胞的增量阈值更高，并且在中等背景强度下最终会消失在视锥细胞增量阈值之上。这一结果表明背景直径确实会影响视杆系统的饱和度。然而，当对较小背景的适应仅限于每个实验环节中对单一背景强度进行5分钟的暴露时，那么针对该背景的阈值是由视杆细胞而非视锥细胞介导的，并且与针对8度背景的视杆细胞阈值相当。因此，在这些刺激条件下，除非对较小背景的适应时间延长，否则背景大小显然不会影响视杆系统的饱和度。基于先前的研究，我们认为在长时间适应条件下小背景对视杆细胞的脱敏作用是由于视网膜后机制。
