The postauricular reflex is a muscular reaction that occurs behind the ear in response to short, abrupt sounds. Its magnitude increases with louder eliciting sounds, rotating the eyes in the direction of the eliciting sound, and flexing the head forward. The reflex exhibits prepulse inhibition, especially during attention to complex foreground stimuli. Its magnitude is larger (or potentiated) during pleasant than during neutral pictures, sounds, and videos that are highly arousing. This pattern is particularly evident for erotic, food, and nurturant scenes, suggesting it assesses more than just appetitive processing. This reflex’s potentiation varies across development; positively correlates with personality traits associated with well-being; and negatively correlates with such psychopathologies as depression, schizophrenia, and opioid dependence. It appears distinct from and uncorrelated with the startle blink reflex. New data suggest that activity in left frontal areas generates postauricular reflex potentiation during pleasant versus neutral pictures.