Herzog E D, Powers M K, Barlow R B
Department of Bioengineering and Neuroscience, Syracuse University, USA.
Vis Neurosci. 1996 Jan-Feb;13(1):31-41. doi: 10.1017/s0952523800007100.
Male horseshoe crabs, Limulus polyphemus, use their eyes to locate mates day and night. We investigated their ability to detect targets of different size and contrast in a mating area of Buzzards Bay, Cape Cod, MA. We found that males can see large, high-contrast targets better than small, low-contrast ones. For targets of the same size, animals must be about 0.1 m closer to a low-contrast target to see it as well as a high-contrast one. For targets of the same contrast, animals must be approximately 0.2 m closer to a small target to see it as well as one twice as large. A decrease of 0.05 steradians in the size of the retinal image of a target can be compensated by a four-fold increase in contrast. About 60% of the animals detect black targets subtending 0.110 steradians (equivalent to an adult female viewed from about 0.56 m), while only 20% detect targets subtending 0.039 steradians. This study shows that horseshoe crabs maintain about constant contrast sensitivity under diurnal changes in light intensity in their natural environment. As a consequence of circadian and adaptive mechanisms in the retina, male horseshoe crabs can detect female-size objects about equally well day and night.
雄性鲎（美洲鲎）日夜都利用眼睛来寻找配偶。我们在马萨诸塞州科德角秃鹰湾的一个交配区域研究了它们探测不同大小和对比度目标的能力。我们发现，雄性鲎对大的、高对比度目标的视觉效果要优于小的、低对比度目标。对于相同大小的目标，动物必须离低对比度目标近约0.1米才能像看清高对比度目标一样看清它。对于相同对比度的目标，动物必须离小目标近约0.2米才能像看清两倍大的目标一样看清它。目标视网膜图像大小减少0.05球面度可通过对比度提高四倍来补偿。约60%的动物能探测到张角为0.110球面度的黑色目标（相当于从约0.56米处看成年雌性），而只有20%的动物能探测到张角为0.039球面度的目标。这项研究表明，在自然环境中光照强度的昼夜变化下，鲎的对比度敏感度保持大致恒定。由于视网膜中的昼夜节律和适应性机制，雄性鲎在白天和晚上探测雌性大小物体的能力大致相同。
