To investigate how indistinct information in a nonverbal stimulus affects the categorizing process of that stimulus, we observed the event-related potentials (ERP) elicited by arrows, which indicate distinct (rightlleft or upward) or indistinct (to some extent different from rightlleft or upward) directions. In three experiments, participants were required three different judgments on the direction of these arrows. The results from these experiments suggest that the N2 and P3b components of ERP relate to the processes on which discrimination and categorization of nonverbal stimuli depend, while it was not demonstrated the N400 is sensitive to the incongruity between verbal and nonverbal directional information.