Gegenfurtner K R, Mayser H M, Sharpe L T
Max-Planck-Institut für biologische Kybernetik, Tübingen, Germany.
J Opt Soc Am A Opt Image Sci Vis. 2000 Sep;17(9):1505-15. doi: 10.1364/josaa.17.001505.
Although the spatial and temporal properties of rod-mediated vision have been extensively characterized, little is known about scotopic motion perception. To provide such information, we determined thresholds for the detection and identification of the direction of motion of sinusoidal grating patches moving at speeds from 1 to 32 deg/s, under scotopic light levels, in four different types of observers: three normals, a rod monochromat (who lacks all cone vision), an S-cone monochromat (who lacks M- and L-cone vision), and four deuteranopes (who lack M-cone vision). The deuteranopes, whose motion perception does not differ from that of normals, allowed us to measure rod and L-cone thresholds under silent substitution conditions and to compare directly the perceived velocity for moving stimuli detected by either rod or cone vision at the same light level. We find, for rod as for cone vision, that the direction of motion can be reliably identified very near to detection threshold. In contrast, the perceived velocity of rod-mediated stimuli is reduced by approximately 20% relative to cone-mediated stimuli at temporal frequencies below 4 Hz and at all intensity levels investigated (0.92 to -1.12 log cd m(-2)). Most likely, the difference in velocity perception is distal in origin because rod and cone signals converge in the retina and further processing of their combined signals in the visual cortex is presumably identical. To account for the difference, we propose a model of velocity, in which the greater temporal averaging of rod signals in the retina leads to an attenuation of the motion signal in the detectors tuned to high velocities.
尽管视杆介导视觉的空间和时间特性已得到广泛表征，但对于暗视运动感知却知之甚少。为了提供此类信息，我们测定了在暗视光照水平下，四种不同类型观察者检测和识别以1至32度/秒速度移动的正弦光栅斑块运动方向的阈值：三名正常人、一名视杆单色视者（缺乏所有视锥视觉）、一名S视锥单色视者（缺乏M视锥和L视锥视觉）以及四名绿色盲患者（缺乏M视锥视觉）。绿色盲患者的运动感知与正常人无异，这使我们能够在静默替代条件下测量视杆和L视锥阈值，并直接比较在相同光照水平下由视杆或视锥视觉检测到的移动刺激的感知速度。我们发现，对视杆视觉和视锥视觉而言，在非常接近检测阈值时就能可靠地识别运动方向。相比之下，在低于4赫兹的时间频率以及所有研究的强度水平（0.92至 -1.12 log cd m(-2)）下，视杆介导刺激的感知速度相对于视锥介导刺激降低了约20%。速度感知的差异很可能源于视网膜前端，因为视杆和视锥信号在视网膜中汇聚，并且它们在视觉皮层中对组合信号的进一步处理大概是相同的。为了解释这种差异，我们提出了一个速度模型，其中视网膜中视杆信号更大的时间平均导致调谐到高速度的探测器中的运动信号衰减。
