APA Dictionary of Psychology

the hypothesis that the range of cues attended to is inversely related to the degree of arousal; that is, in a state of increased arousal, attention narrows and fewer environmental stimuli are focused on. The hypothesis was proposed as an explanation of Yerkes–Dodson law, which describes the relationship between arousal and performance. [proposed in 1959 by J. A. Easterbrook, 20th-century Canadian psychologist]