Abstract: Length effect indicated that the duration cognitive or neural mechanism would be different with the difference of duration. “Same” mechanism hypothesis viewed the same processing mechanism was used, and it could be explained by Scalar Timing Theory, while “different” mechanism hypothesis viewed the different processing mechanism was used, 2-3 seconds, 1 second, 1/2 second, and 1/3 second etc. could be used to label different mechanism. Future research seems to investigate four kinds of issues, e.g. reliability of previous evidences, diversity of standard, determinacy of boundary location, and applicability of theories.

Key words: length effect, “same” mechanism hypothesis, “different” mechanism hypothesis, Dual-Processing Theory, Scalar Timing Theory