A couple of psychologists did research into bank investment bonuses. They found small performance bonuses (compared to salary) improved work, but large bonuses only encouraged the worker to work for the bonus (usually by being less ethical or careful). When presented with this research, bank bosses were fascinated and agreed with the findings. The researchers then pointed out that the bosses were in the same group of over-bonused workers. The big-wigs decided they were quite trustworthy and the bonuses had no effect on their behaviour... Since that study, this article suggests that virtually all bonus effects are negative ones...
https://www.psychologytoday.com/au/blog/the-homework-myth/201609/the-bonus-effect
Biting the hand that feeds IT
