| Abstract: | In a test of the arousal hypothesis of introversion-extraversion, subjects were pre- and post-tested on practice Graduate Record Examination verbal performance items while administered caffeine at either 0, 2, or 4 mg/kg of body weight. Introverts increased dramatically in performance between the 0 and 2 mg/kg conditions and then decreased even more dramatically between the 2 and 4 mg/kg conditions. Extraverts showed decrements in performance at the 0 mg/kg level, improved slightly at the 2 mg/kg level, and showed marked improvement at the 4 mg/kg level. Further analyses revealed that introverts increased in both speed and accuracy at low levels of stimulation but then decreased in both at higher levels of stimulation. Extraverts showed continued increases in speed and accuracy across the increasing arousal levels. |
