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Abstract The naming of pictures is typically thought to require sequential access to stored structural knowledge about objects, to semantic knowledge, and to a stored phonological description. Access to these different types of knowledge may constitute discrete processing stages; alternatively, it may be that information is transmitted continuously (in cascade) from one type of description to the next. The discrete stage and the cascade accounts make different predictions about the effects of structural and semantic similarity between objects on picture naming. The discrete stage account maintains that the effects of structural similarity should be confined to the process of accessing an object's structural description, and the effects of semantic similarity should be confined to the process of accessing semantic knowledge. The cascade account predicts that the effect of both variables may be passed on to subsequent processing stages. We present evidence drawn from both normal observers and from a patient with an acquired disorder of picture naming, which supports the cascade model. The implications of such a model for understanding acquired disorders of visual object processing are discussed.