Jacobs G H, Birch D G, Blakeslee B
Department of Psychology, University of California, Santa Barbara, CA 93106 U.S.A.
Behav Processes. 1982 Dec;7(4):367-75. doi: 10.1016/0376-6357(82)90008-0.
The visual sensitivity of tree squirrels from three different species (two western gray squirrels, Sciurus griseus; three fox squirrels, Sciurus niger; and an eastern gray squirrel, Sciurus carolinensis) was measured for spatial patterns defined by luminance differences. Spatial contrast sensitivity functions were determined in behavioral discrimination experiments in which the stimuli were sinusoidally-modulated gratings. At an average luminance level of 3.4 cd/m(2) these squirrels were maximally sensitive to spatial frequencies of about 0.5 cycles/degree (c/d). These experiments, in conjunction with additional measurements involving discrimination of square-wave grating patterns, also indicate that the finest gratings these squirrels can discriminate average 2.2 c/d (SD = 0.42 c/d). There are no obvious differences in resolution acuity among the three species. Grating acuity also was measured at a much higher luminance level (340 cd/m(2)). The results of this experiment indicate that the spatial acuity of the tree squirrel increases with luminance level, reaching a maximum of 3.9 c/d at 340 cd/m(2).
对三种不同种类的松鼠（两只西部灰松鼠，即灰松鼠；三只狐松鼠，即黑松鼠；以及一只东部灰松鼠，即卡罗来纳州灰松鼠）的视觉敏感度进行了测量，测量对象是由亮度差异定义的空间模式。在行为辨别实验中确定了空间对比敏感度函数，实验中的刺激物是正弦调制光栅。在平均亮度水平为3.4坎德拉每平方米（cd/m²）时，这些松鼠对约0.5周/度（c/d）的空间频率最为敏感。这些实验，再加上涉及方波光栅图案辨别的额外测量，还表明这些松鼠能够辨别的最精细光栅平均为2.2 c/d（标准差 = 0.42 c/d）。这三个物种之间在分辨敏锐度上没有明显差异。还在高得多的亮度水平（340 cd/m²）下测量了光栅敏锐度。该实验结果表明，松鼠的空间敏锐度随亮度水平增加，在340 cd/m²时达到最大值3.9 c/d。
