The current study tackles a long standing question of whether comprehenders perform structural revision when it is not forced by grammar or not. Using an eye-tracking reading paradigm, we addressed this issue by making use of global structural ambiguity in Japanese. Our results show that comprehenders initially associate a relative clause with the first potential head noun and that they revise this analysis when the second noun is lexico-semantically possible as the relative clause head, but do not when it is impossible. The results are incompatible with the Revision as Last Resort hypothesis. Instead, they support the parsing with unforced revision that is immediately sensitive to lexical properties. We argue that our results cannot be accounted for by serial modular processing models but that they can be explained by ranked-parallel interactive processing models. Furthermore, we propose that head-finality is a key factor involved in the availability of unforced revision.