Abstract: In the present study, two experiments were conducted to test the sequential effect of same-different judgment under different ISIs. Two stimuli were successively presented for comparison on each trial. A 2 ( the response types of preceding trial: same, different)×2 ( the response types of present trial: same, different)×6 (ISIs: 100ms, 200ms, 300ms, 400ms, 500ms, 600ms) within-subjects design was used. 21 undergraduates (11 females and 10 males) participated in this study. The results showed that the trials preceded by “same” trials were significantly faster than trials preceded by “different” trials in all conditions. This is called “same” priming effect. The results supported the dual-process model of same-different judgment and indicated that the dual processes work serially

Key words: same-different judgment, sequential effect, “same”-priming effect, interstimulus interval (ISI), dual-process model