A number of studies have found evidence for the so-called ambiguity advantage, i.e., a speed-up in processing ambiguous sentences compared to their unambiguous counterparts. While a number of proposals regarding the mechanism underlying this phenomenon have been made, the empirical evidence so far is far from unequivocal. It is compatible with several theories, including strategic underspecification (Swets et al., 2008), race models (Van Gompel et al., 2000; Logacev and Vasishth, 2016), and a more recentcoactivation-based account (Dillon et al., 2019). While all three classes of theories make matching predictions for the average time to complete RC attachment in ambiguous compared to unambiguous sentences, their predictions diverge with regard to theminimum completion times. I used the speed-accuracy tradeoff procedure to test the predictions of all three classesof theories. According to a hierarchical Bayesian model, the speed-accuracy tradeoff functions (SATFs) for different RC attachment conditions (high, low or ambiguous) show an earlier departure from chance performance in the ambiguous condition than in either of the unambiguous conditions. The results further indicate increased asymptotic accuracy but no increase in processing rate in the ambiguous condition. Taken together, this pattern of results is compatible with the strategic underspecification model, and to a lesser degree with coactivation based accounts.