Fernández-Juricic Esteban, Moore Bret A, Doppler Megan, Freeman Joseph, Blackwell Bradley F, Lima Steven L, DeVault Travis L
Department of Biological Sciences, Purdue University, West Lafayette, Ind., USA.
Brain Behav Evol. 2011;77(3):147-58. doi: 10.1159/000326053. Epub 2011 May 6.
The distribution of ganglion cells in the retina determines the specific regions of the visual field with high visual acuity, and thus reflects the perception of a species' visual environment. The terrain hypothesis proposes that animals living in open areas should have a horizontal visual streak across the retina with high ganglion cell density to increase visual acuity along the horizon. We tested this hypothesis in Canada geese (Branta canadensis) by assessing retinal topography, visual field configuration, and scanning behavior. We found that geese have an oblique rather than a horizontal visual streak across the retina: from a dorsal-nasal to a ventral-temporal position. Geese showed narrow blind areas, which increased the range of their lateral vision, and a relatively large degree of eye movement. Canada geese have relatively wide binocular fields and can see their bill tips. Goose head movement rates were low compared to species with a single fovea, and head movement rates increased in visually obstructed habitats. Canada geese have high acuity across their retina, which would allow them to simultaneously scan the ground and the sky when the head is up and parallel to the ground, as well as align the visual streak with the horizon when the head is tilted downwards. Their visual streak, along with their large eye size, may reduce the need for large amplitude head movements during vigilance bouts in visually unobstructed habitats. Overall, the visual system of geese combines features related to the detection of predators/conspecifics in open areas (visual streak, large lateral field, reduced head movements) as well as visual specializations that would allow for monitoring both the ground and sky (oblique streak) and for extracting and handling of food items (wide binocular fields, visualization of the bill tip).
视网膜中神经节细胞的分布决定了视敏度高的视野特定区域，从而反映了一个物种对视觉环境的感知。地形假说提出，生活在开阔区域的动物视网膜上应该有一条水平视觉带，神经节细胞密度高，以提高沿地平线方向的视敏度。我们通过评估加拿大鹅（Branta canadensis）的视网膜地形图、视野配置和扫描行为来检验这一假说。我们发现，加拿大鹅的视网膜上有一条倾斜而非水平的视觉带：从背鼻侧到腹颞侧。加拿大鹅的盲区狭窄，这增加了它们的侧向视野范围，并且眼球运动程度相对较大。加拿大鹅有相对较宽的双眼视野，能够看到它们的喙尖。与具有单个中央凹的物种相比，加拿大鹅头部的运动速率较低，并且在视觉受阻的栖息地中头部运动速率会增加。加拿大鹅的整个视网膜都有高视敏度，这使它们在头部向上且与地面平行时能够同时扫视地面和天空，以及在头部向下倾斜时使视觉带与地平线对齐。它们的视觉带，连同其较大的眼睛尺寸，可能会减少在视野不受阻的栖息地进行警觉时大幅度头部运动的需求。总体而言，加拿大鹅的视觉系统结合了与在开阔区域检测捕食者/同种个体相关的特征（视觉带、大的侧向视野、减少的头部运动）以及允许监测地面和天空（倾斜视觉带）和提取与处理食物项目（宽双眼视野、看到喙尖）的视觉特化。
