A computational model of semantic memory impairment: Modality specificity and emergent category specificity.

TLDR

The authors present a parallel distributed processing model that partitions semantic knowledge into visual and functional modalities. Experiments demonstrate that lesions to visual or functional components of the model produce category‑specific deficits, reproducing known impairments in living and nonliving items and explaining previously problematic findings such as verbal‑only deficits for living things.

Abstract

It is demonstrated how a modality-specific semantic memory system can account for category-specific impairments after brain damage. In Experiment 1, the hypothesis that visual and functional knowledge play different roles in the representation of living things and nonliving things is tested and confirmed. A parallel distributed processing model of semantic memory in which knowledge is subdivided by modality into visual and functional components is described. In Experiment 2, the model is lesioned, and it is confirmed that damage to visual semantics primarily impairs knowledge of living things, and damage to functional semantics primarily impairs knowledge of nonliving things. In Experiment 3, it is demonstrated that the model accounts naturally for a finding that had appeared problematic for a modality-specific architecture, namely, impaired retrieval of functional knowledge about living things. Finally, in Experiment 4, it is shown how the model can account for a recent observation of impaired knowledge of living things only when knowledge is probed verbally.