Loss of Semantic Memory: Implications for the Modularity of Mind

We report a patient, PP, with semantic dementia who was studied longitudinally over two years. During this period she showed a progressive and profound loss of semantic memory affecting factual knowledge, vocabulary, and object knowledge via all sensory modalities. In the face of this near total dissolution of semantic memory, we have addressed the issue of the fate of other cognitive processes. Our findings suggest that nonverbal problem solving, auditory verbal and spatial short-term memory, the high-level visuoperceptual abilities involved in object constancy, and some basic syntactic processes may operate independently of semantic memory and are therefore independent cognitive modules. In contrast, the integrity of both the phonological representations of words used to produce speech and the representations (or structural descriptions) used to recognise familiar objects appear ultimately to depend on semantic memory.