Motivated by Screaming

I had the most satisfying Eureka experience of my career while attempting to teach flight instructors that praise is more effective than punishment for promoting skill-learning. I was telling them about an important principle of skill training: rewards for improved performance work better than punishment of mistakes. This proposition is supported by much evidence from research on pigeons, rats, humans and other animals.

When I had finished my enthusiastic speech, one of the most seasoned instructors in the audience raised his hand and made a short speech of his own. He began by conceding that positive reinforcement might be good for the birds, but he denied that it was optimal for flight cadets. This is what he said,

“On many occasions I have praised flight cadets for clean execution of some aerobatic maneuver. The next time they try the same maneuver they usually do worse. On the other hand, I have often screamed into a cadet’s earphone for bad execution, and in general he does better one his next try. So please don’t tell us that reward works and punishment does not, because the opposite is the case.”

This was a joyous moment of insight, in which I saw in a new light a principle of statistics that I had been teaching for years. The instructor was right – but he was also completely wrong! His observation was astute and correct: occasions on which he praised a performance were likely to be followed by a disappointing performance, and punishments were typically followed by an improvement. But the inference he had drawn about the efficacy of reward and punishment was completely off the mark.

What he had observed is known as regression to the mean, which in that case was due to random fluctuations in the quality of the performance. Naturally, he praised only a cadet whose performance was far better than average. But the cadet was probably just lucky on that particular attempt and therefore likely to deteriorate regardless of whether or not he was praise. Similarly, the instructor would shout in to a cadet earphones only when the cadet’s performance was usually bad and therefore likely to improve regardless of what the instructor did. The instructor had attached a causal interpretation to the inevitable fluctuations of a random process.

Daniel Kahneman, Thinking Fast and Thinking Slow