89 Horse Sense

The crowd stirred and whispered in awe, as, on the stage, the horse slowly tapped out the beat. Everyone became tense and quiet as the number of taps neared the correct answer to the horse trainer's question. After the final tap, the horse paused, seemed to look around, and stopped. The crowd went wild!

The horse's name was Clever Hans, the Educated Horse, and he was featured in a vaudeville act in the early 1900s in Europe. When asked a complicated mathematical question by his owner, Clever Hans would tap out the correct answer with his hooves. For example, if the answer was sixty-eight, Hans would tap six with his left hoof and eight with his right hoof. Even more remarkable, the owner would leave the room after asking the question, so there could be no secret signal between owner and horse. A mere animal seemed to be accomplishing a highly technical human skill!

It wasn't until years later that the secret of the trick was revealed. The owner had trained Clever Hans to respond to slight signals. The horse became so sensitive that he learned when to stop from the crowd's reaction. Members of the audience would unknowingly start or give some other unconscious signal when Hans reached the right answer. Modern scientists now warn against the Clever Hans syndrome, whereby researchers unwittingly give clues to their animal subjects about actions they would like to see performed!

89 马的“智慧”

观众们骚动起来，敬畏地窃窃私语，舞台上，那匹马正缓慢地敲打出节拍。当敲击次数接近驯马师问题的正确答案时，所有人都变得紧张而安静。最后一次敲击后，马停顿了一下，似乎环顾了四周，然后停了下来。观众们沸腾了！

这匹马名叫“聪明的汉斯”，也就是“受过教育的马”，20世纪初它在欧洲的杂耍表演中很受欢迎。当主人向它提出一个复杂的数学问题时，聪明的汉斯会用蹄子敲出正确答案。例如，如果答案是68，汉斯会用左蹄敲6下，右蹄敲8下。更值得注意的是，主人问完问题后会离开房间，这样主人和马之间就不会有秘密信号。一只普通的动物似乎掌握了一项高度技术性的人类技能！

直到几年后，这个把戏的秘密才被揭开。主人训练聪明的汉斯对细微的信号做出反应。这匹马变得非常敏感，它能从观众的反应中知道什么时候该停下来。当汉斯得出正确答案时，观众会不知不觉地做出开始的动作或其他无意识的信号。现代科学家现在警告要警惕“聪明汉斯综合征”，即研究人员无意中向他们的动物实验对象透露了他们希望看到的动作的线索！