Interpreting sentences requires comprehenders to answer the basic question of who did what to whom. Previous research has shown that role assignment sometimes occurs early, even before a sentence is linguistically disambiguated from alternate constructions. In contrast, previous work has also shown that role assignment sometimes occurs late, even after linguistic disambiguation. Why do differences in the timing of role assignment occur? In this talk I report on a visual world eye-tracking study that addresses possible accounts for these observed processing differences.