UX Glossary terms starting with letter Y
Psychologists Yerkes and Dodson demonstrated, in 1908, the relationship between physiological arousal (stress) and performance: Performance increases with arousal, but only to a point. When arousal is too high, performance decreases.
Yerkes RM, Dodson JD (1908). "The relation of strength of stimulus to rapidity of habit-formation". Journal of Comparative Neurology and Psychology.