There have been many attempts to examine the relationship between strength-sensivity
and Eysenck's extraversion-introversion dimension. Eysenck (1966) predicted that introverts would be the weak type of nervous system and extraverts would be the strong type of nervous system. But，the results from the reaction time studies concerning difference between introverts and extraverts are inconsistent. In the present experiment，simple motor reaction time method for measuring strength-sensitivity was employed with 3 groups (introverts，ambiverts，extraverts)， introverts were observed to have a faster reaction time than extraverts，there were significant mean differences between introverts and extraverts at the two stimulus intensities (40 dB and 80 dB).