In this paper, we investigate the effects of readers' incorrect knowledge on the on-line comprehension processes during reading of science texts, with an eye towards examining the conditions that encourage revision of such knowledge. We employed computational (Landscape Model) and empirical (think-aloud and reading times) methods to compare comprehension processes by readers with correct and incorrect background knowledge, respectively. Science texts were presented in either regular or refutation versions; Prior research using off-line methods suggests that refutation versions promote revision in readers with incorrect knowledge. The results of the current study indicate that incorrect knowledge systematically influences both type and content of processing. Moreover, simultaneous activation of correct and incorrect conceptions during reading plays an essential role in knowledge revision: The computational simulations show that refutation texts create optimal circumstances for co-activation of the incorrect and correct conceptions and the empirical data show that such a co-activation is associated with inconsistency detection and revision activities by the readers with incorrect knowledge. These findings provide insights in the effects of mis-conceptions on the on-line text processing and have important implications for the development of methods for achieving revision during reading.