Additivity of factor effects in reading tasks is still a challenge for computational models: Reply to Ziegler, Perry, and Zorzi (2009).

J. C. Ziegler, C. Perry, and M. Zorzi (2009) have claimed that their connectionist dual process model (CDP+) can simulate the data reported by S. O'Malley and D. Besner. Most centrally, they have claimed that the model simulates additive effects of stimulus quality and word frequency on the time to read aloud when words and nonwords are randomly intermixed. This work represents an important attempt given that computational models of reading processes have to date largely ignored the issue of whether it is possible to simulate additive effects. Despite CDP+'s success at capturing many other phenomena, it is clear that CDP+ fails to capture the full pattern seen with skilled readers in these experiments.