In the proposed project, we examine the effects of model based semantic treatment on improving lexical access defects in aphasia. We plan to build on previous work highlighting the role of theories of lexical processing in improving lexical access. In the proposed project, we plan to establish a data set of treatment methods for lexical access deficits that include oral confrontation naming and category fluency. All our treatment methods are focused on maximizing generalization to untrained semantically related items within the semantic category. Our treatment approach for lexical access deficits that utilizes the semantic complexity hypothesis. We define semantic complexity within a category in terms of: a) lesser degree of overlap between the item and prototype; b) greater variation of semantic features; and c) hierarchically greater distance between the prototype and item in a multidimensional space. Our previous work has demonstrated that training the more complex atypical examples of animate categories results in generalization to the less complex typical examples in aphasic patients with naming deficits. In this project, we plan to further build this hypothesis and demonstrate the effects of complexity on typicality for a variety of categories such as inanimate categories, well defined categories and ad hoc categories. We also extend our investigations to understand the mechanisms underlying the relationship between typicality and complexity in normal and brain damaged individuals. We will accomplish this through online category verification tasks across different types of semantic categories.