填空题

To understand the importance of controlled observation in psychology, we look at a horse by the name of Hans. Hans could reason and "talk". Hans had been trained by a math teacher, Mr. Osten, to communicate by tapping forefoot and moving his head. A head nod meant yes, and a shake suggested no. Mr. Osten developed a code for verbal information in which each letter was represented by a pair of numbers. The letter A was coded as one tap, pause, one tap, and the letter I was three taps, pause, two taps. Once Hans learned to tap his foot or move his head. when questioned, he was given simple problems and then fed a piece of bread or carrot for correct responses. By the end of his training, Hans could spell words, and he excelled in math. He became a hero in Germany — his picture was on wine bottles and toys.
An official commission examined the horse, testing him to see if he really did all the things claimed. They came away very impressed and issued a statement that there was no evidence of any intentional influence or aid on the part of Hans’ questioners.
But there was one scientist who was not so sure that Hans was as intelligent as he had been portrayed. Oskar Pfungst, a sharp observer, had detected that Hans always faced his questioners. Pfungst hypothesized that this might have something to do with his math ability. The scientist set up a very simple experiment. He wrote numbers on a card and held them up one at a time, asking Hans to tap out the numbers written on each card. Half of the cards were held so that only Hans, not Pfungst himself, could see. Hans was his usual brilliant self, getting 92% of them correct. But for the numbers Pfungst could not see, Hans was no longer a brilliant horse, getting 8% correct.
Pfungst repeated the experiment over and over again with nearly the same results. He observed Hans with his other questioners. As soon as they stated the problem to Hans, most questioners would turn their head and upper body slightly. When the correct number of foot taps had been made by Hans, the questioner would move his head upward. Despite his years of work with the horse, Mr. Osten had never dreamed that Hans had learnt to "read" him. He felt angry and betrayed by the horse.
Thus we can see that experts sometimes can be wrong and that what sometimes seems to be the troth may be a false impression. Even experts can be fooled if they don’t make appropriate use of research procedures to check their observations.
(447 words) Oskar Pfungst discovered that Hans performed badly in the math work when ______ .