Nested Incremental Modeling in the Development of Computational Theories: The CDP Model of Reading Aloud Conrad Perry Swinburne University of Technology Johannes C. Ziegler Centre National de la Recherche Scientifique and Universite ´ de Provence Marco Zorzi Universita ` di Padova At least 3 different types of computational model have been shown to account for various facets of both normal and impaired single word reading: (a) the connectionist triangle model, (b) the dual-route cascaded model, and (c) the connectionist dual process model. Major strengths and weaknesses of these models are identified. In the spirit of nested incremental modeling, a new connectionist dual process model (the CDP model) is presented. This model builds on the strengths of 2 of the previous models while eliminating their weaknesses. Contrary to the dual-route cascaded model, CDP is able to learn and produce graded consistency effects. Contrary to the triangle and the connectionist dual process models, CDP accounts for serial effects and has more accurate nonword reading performance. CDP also beats all previous models by an order of magnitude when predicting individual item-level variance on large databases. Thus, the authors show that building on existing theories by combining the best features of previous models—a nested modeling strategy that is commonly used in other areas of science but often neglected in psychology—results in better and more powerful computational models. Keywords: reading, naming, word recognition, dual-route cascaded model, connectionist models At least since Huey (1908), experimental and cognitive psychol- ogists have been interested in describing the processes underlying skilled reading in a precise and detailed manner. Early attempts were purely verbal and qualitative, and box-and-arrow models of the reading process were ubiquitous (see, e.g., Morton, 1969). With the emergence of connectionism, the modeling of aspects of the reading process experienced a quantum leap (McClelland & Rumelhart, 1981; Rumelhart & McClelland, 1982; Seidenberg & McClelland, 1989). Purely verbal theories were successively re- placed by explicit computational models. These models can pro- duce highly detailed simulations of various aspects of the reading process, including word recognition and reading aloud (e.g., Colt- heart, Curtis, Atkins, & Haller, 1993; Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001; Grainger & Jacobs, 1996; Harm & Seidenberg, 1999, 2004; Norris, 1994; Plaut, McClelland, Seiden- berg, & Patterson, 1996; Seidenberg & McClelland, 1989; Zorzi, Houghton, & Butterworth, 1998b). In addition, lesioning the mod- els in various ways made it possible to compare the behavior of the models to that of neuropsychological patients with various reading impairments (i.e., acquired dyslexia; see Denes, Cipolotti, & Zorzi, 1999, for a review). This type of modeling improved understand- ing of both the fundamental processes involved in reading single words aloud and the causes underlying various reading disorders (see Zorzi, 2005, for a review). Despite the huge progress in developing computational models, each model has its own fundamental limitations and problems in accounting for the wide range of available empirical data (see Previous Models section). The goal of the present research was to design a new model by building on the strengths of some of the previous models and eliminating their weaknesses. In other sci- ences, it is standard practice that a new model accounts for the crucial effects accounted for by the previous generations of the same or competing models. This strategy, often neglected in psy- chology, has sometimes been referred to as nested modeling:A Conrad Perry, Faculty of Life and Social Sciences, Swinburne Univer- sity of Technology, Melbourne, Australia; Johannes C. Ziegler, Labora- toire de Psychologie Cognitive, Centre National de la Recherche Scienti- fique and Universite ´ de Provence, Marseille, France; Marco Zorzi, Dipartimento di Psicologia Generale, Universita ` di Padova, Padova, Italy. All authors contributed equally to this work; the order of authorship is alphabetical. An executable version of CDP can be downloaded at http://ccnl.psy.unipd.it/CDP.html. Data sets for all benchmark effects and all other studies included in this article can also be found at this site. Part of this work was done while Conrad Perry was supported by a University Development Fund grant from The University of Hong Kong. This re- search was also partially funded by a Procore travel grant (28/03T and 07806VE) between France and Hong Kong and a grant from the University of Padova to Marco Zorzi. We thank Florian Hutzler for some of the triangle model simulations, Debra Jared for providing the raw data of Jared (2002), Brad Aitken for providing computing facilities, and Max Coltheart for many helpful dis- cussions. Thanks are extended to Dave Balota, Derek Besner, Debra Jared, and David Plaut for very helpful comments. Correspondence concerning this article should be addressed to Johannes C. Ziegler, Laboratoire de Psychologie Cognitive, Po ˆ le 3C, Case D, CNRS et Universite ´ de Provence, 3 place Victor Hugo, 13331 Marseille, Cedex 3, France. E-mail: Johannes C. Ziegler, ziegler@up.univ-mrs.fr; Conrad Perry, conradperry@gmail.com; Marco Zorzi, marco.zorzi@unipd.it Psychological Review Copyright 2007 by the American Psychological Association 2007, Vol. 114, No. 2, 273–315 0033-295X/07/$12.00 DOI: 10.1037/0033-295X.114.2.273 273