Letter processing in reading and spelling: Some dissociations

Abstract

We describe the complex pattern of spared and impaired performance observed in a neurologically impaired subject on a number of letter processing tasks including: written letter naming, alphabetization, matching across typecase and font, oral and written spelling to dictation, and across-case letter priming. The observed dissociation in performance between the naming of written letters and the naming of letters in oral spelling as well as the dissociation between oral spelling and written spelling are shown to support a model of letter processing in which a distinction is drawn between visuo-spatial and abstract levels of letter representation. We also describe symmetrical deficits in the reading and writing of letters. These can be understood: in reading, as the result of an impairment to the processes which mediate the conversion of visuo-spatial letter representations to abstract representations, and in writing, as a deficit to the processes which negotiate the apparently reverse operation. This finding is interpreted within the context of the notions of neural and functional proximity and we raise the possibility that processes which perform distinct computations may, nonetheless, share certain computational resources.