BRAIN AND LANGUAGE 15, 161-189 (1982) The Semantic Deficit Hypothesis: Perceptual Parsing and Object Classification by Aphasic Patients ALFONSO CARAMAZZA AND RITA SLOAN BERNDT The Johns Hopkins Universit~~ AND HIRAM H. BROWNELL Aphasia Research Center, Boston Veterans’ Administration Hospital Many aphasic patients are impaired in their ability to provide or to recognize the names of objects, but little is known about the processing deficits that underlie these difficulties. In this report, a model of object naming/name recognition is proposed, and a prediction is tested concerning one possible functional locus of impairment in name-recognition and object-naming disorders. A subgroup of aphasic patients is found to be impaired in the ability to perform perceptual similarity judgments for pairs of stimulus objects, and to be unable to classify the objects into one of two lexical categories. It is concluded that the classification disorder suffered by these patients results from an impairment at the level of the semantically guided perceptual parsing of objects. The relationship between words and the objects in the world that they signify is complex, undoubtedly involving considerably more than a series of one-to-one associations between words and objects. Between the sight- ing of an object and the articulation of its name, or between the perception of a word and the selection from alternatives of the object it represents, the cognitive system must perform considerable sifting and weighting of information, categorization of events, and matching of different sets of abstract conceptual elements. Although some progress has been made This research was supported by NIH Grant 14099 to the Johns Hopkins University. We would like to thank the staff members of the Department of Audiology and Speech Pa- thology, Fort Howard VA Medical Center, and the Department of Hearing and Speech, The Good Samaritan Hospital, for their cooperation in this research project. We are especially grateful to Michael Giordano for the time and care that he devoted to performing the data analyses reported here. Address correspondence to: Alfonso Caramazza, De- partment of Psychology, The Johns Hopkins University, Baltimore, MD 21218. 161 0093-934X/82/010161-29$02.00/0 Copyright 0 1982 by Academic Press. Inc. All rights of reproduction in any form reserved.