射水鱼看上去能注意到与背景排列方向不同的物体，科学家在传统上把这种特点与哺乳动物的大脑联系起来。射水鱼是老练的猎手，具有喷水击落昆虫猎物的不寻常的能力。为了确定射水鱼是否具有通常与哺乳动物视觉皮层有联系的视觉选择性行为，Ohad Ben-Shahar及其同事首先训练了5条射水鱼射击这些鱼的水缸上方显示昆虫图像的液晶显示器屏幕。然后，这组科学家把昆虫的图像替换成了有方向或无方向性的背景上的各种位置和方向的黑条。

通过几百次试验中的精心控制的一系列实验，这组科学家确定了这种鱼更多地射击与背景方向不同的目标，而非那些与背景方向类似的物体以及那些在无方向性背景上的物体。让人类受试者接受类似刺激的试验提示，这种鱼的“方向性选择”行为不是依赖于刺激的。这组作者提出，不论这种鱼和人类进化出的这种能力来自一个共同祖先还是各自独立进化出来的，该研究显示了基于方向性的视觉选择对于高效视觉处理具有普遍性和基础性。

英文摘要：

PNAS doi: 10.1073/pnas.1005446107

Orientation saliency without visual cortex and target selection in archer fish
Alik Mokeicheva,b, Ronen Segevb,c,1, and Ohad Ben-Shahara,b,1,2

Our visual attention is attracted by salient stimuli in our environment and affected by primitive features such as orientation, color, and motion. Perceptual saliency due to orientation contrast has been extensively demonstrated in behavioral experiments with humans and other primates and is believed to be facilitated by the functional organization of the primary visual cortex. In behavioral experiments with the archer fish, a proficient hunter with remarkable visual abilities, we found an orientation saliency effect similar to that observed in human subjects. Given the enormous evolutionary distance between humans and archer fish, our findings suggest that orientation-based saliency constitutes a fundamental building block for efficient visual information processing.