Abstract: Event-related brain potentials were measured when 13 normal young participants finished four kinds of conditional reasoning (MP, AC, DA, MT) tasks and one kind of baseline task(BS). Results showed that there were no amplitude modulations of early components. However MP and DA elicited a more positive EPR deflection on the left and a more negative EPR deflection on the right hemisphere than did BS task in the time window from 450~1100 msec after onset of the stimuli 2. On the contrary MT and AC elicited a more negative EPR deflection on the left and a more positive EPR deflection on the right hemisphere than did BS task in the time window form 450~1100 msec. These ERP components elicited by five different tasks might reflect that right and left hemisphere have different ability of cognitive process in reasoning. In additional Voltage map of the difference wave between reasoning tasks and baseline task showed strong activity in frontal-temporal pathway, Our result support dual-process theory (Goel)

Key words: conditional reasoning, rule theory, model theory, event-related brain potentials