Declining object recognition performance in semantic dementia: A case for stored visual object representations

ABSTRACT

The role of the semantic system in recognizing objects is a matter of debate. Connectionist theories argue that it is impossible for a participant to determine that an object is familiar to them without recourse to a semantic hub; localist theories state that accessing a stored representation of the visual features of the object is sufficient for recognition. We examine this issue through the longitudinal study of two cases of semantic dementia, a neurodegenerative disorder characterized by a progressive degradation of the semantic system. The cases in this paper do not conform to the “common” pattern of object recognition performance in semantic dementia described by Rogers, T. T., Lambon Ralph, M. A., Hodges, J. R., & Patterson, K. (2004). Natural selection: The impact of semantic impairment on lexical and object decision. Cognitive Neuropsychology, 21, 331–352., and show no systematic relationship between severity of semantic impairment and success in object decision. We argue that these data are inconsistent with the connectionist position but can be easily reconciled with localist theories that propose stored structural descriptions of objects outside of the semantic system.

KEYWORDS:

• Semantic dementia
• object recognition
• over-regular object test