Testing Assumptions in Computational Theories of Aphasia

Abstract We present the performances of 13 aphasic patients on a picture-naming task and attempt to model these data using computer simulations. We systematically manipulate the assumptions underlying several interactive, two-step, spreading-activation models, including the proposals of Dell et al. (1997), Foygel and Dell (2000), and Rapp and Goldrick (in press). Using a numerical regres-sion procedure and multiple views of each model's possible output, we find that peripheral pragmatic assumptionsplay a role equal to that of theoretically more central model components. None of the models we consider can account for all of the patients, leading us to conclude that one or more of the assumptions underlying each model is flawed. We argue that there are strong limitations on the conclusions that can legitimately be drawn from such simulation studies but that close analysis of individual patients can allow sound testing of potentially more accurate models.