School of Psychology and Neuroscience, University of St. Andrews, St. Andrews, Fife KY16 9JP, UK.
Division of Psychology, Social and Health Sciences, Abertay University, Dundee, DD1 1HG, UK.
Sci Rep. 2017 Oct 20;7(1):13672. doi: 10.1038/s41598-017-13914-y.
Countershading is a ubiquitous patterning of animals whereby the side that typically faces the highest illumination is darker. When tuned to specific lighting conditions and body orientation with respect to the light field, countershading minimizes the gradient of light the body reflects by counterbalancing shadowing due to illumination, and has therefore classically been thought of as an adaptation for visual camouflage. However, whether and how crypsis degrades when body orientation with respect to the light field is non-optimal has never been studied. We tested the behavioural limits on body orientation for countershading to deliver effective visual camouflage. We asked human participants to detect a countershaded target in a simulated three-dimensional environment. The target was optimally coloured for crypsis in a reference orientation and was displayed at different orientations. Search performance dramatically improved for deviations beyond 15 degrees. Detection time was significantly shorter and accuracy significantly higher than when the target orientation matched the countershading pattern. This work demonstrates the importance of maintaining body orientation appropriate for the displayed camouflage pattern, suggesting a possible selective pressure for animals to orient themselves appropriately to enhance crypsis.
反向阴影是动物中一种普遍存在的图案，即通常面向最高照度的那一侧较暗。当与特定的光照条件和相对于光场的身体方向相匹配时，反向阴影通过平衡由于照明产生的阴影来最小化身体反射的光梯度，因此经典上被认为是一种用于视觉伪装的适应。然而，当相对于光场的身体方向不是最佳时，伪装效果是否以及如何降低，这一点从未被研究过。我们测试了身体方向对于提供有效视觉伪装的反向阴影的行为限制。我们要求人类参与者在模拟的三维环境中检测一个反向阴影目标。目标在参考方向上对于伪装是最佳的，并且以不同的方向显示。当偏离超过 15 度时，搜索性能显著提高。与目标方向与伪装图案匹配的情况相比，检测时间明显更短，准确性明显更高。这项工作表明，保持与显示的伪装图案相适应的身体方向的重要性，这表明动物可能有一种选择压力，使它们自己适应环境以增强伪装效果。
