INTEGRATING SEMANTIC INFORMATION DESPITE SYNAPTIC DEPRESSION: A CONNECTIONIST
ACCOUNT OF "ACCESS" AND "DEGRADED-STORE" SEMANTIC IMPAIRMENTS
David C. Plaut and Stephen J. Gotts
Department of Psychology, Carnegie Mellon University, and the Center for the
Neural Basis of Cognition, Pittsburgh, PA.
Click here to view an
electronic version of the poster.
Neuropsychological studies of patients with acquired semantic impairments have
yielded two distinct and contrasting patterns of performance in a
spoken-word/picture matching task (Warrington & Cipolotti, 1996, Brain).
"Access/refractory" patients are strongly influenced by presentation rate,
semantic relatedness of distractors, and repetition, but are relatively
unaffected by lexical frequency. "Degraded-store" patients, by contrast, are
strongly affected by lexical frequency but not by presentation rate, semantic
relatedness, or repetition.
Our account of these patterns of performance is based on the role of language
processes in maintaining and integrating semantic information over time in the
face of synaptic depression---the tendency of cortical neurons to exhibit a
response decrement under repeated stimulation. We present a connectionist
network which learns to compensate for synaptic depression in posterior
semantic areas by building up strong connections between these and more frontal
regions of the network responsible for semantic maintenance. Damage to these
frontal regions leaves semantic representations vulnerable to synaptic
depression, producing the pattern of data associated with semantic
"access/refractory" impairments. Damage to the semantic representations
themselves, on the other hand, spares the ability to maintain residual semantic
information, producing the pattern of data associated with "degraded-store"
semantic impairments. The instantiation of synaptic depression in the model
also accounts for the occurrence of semantic satiation in normal subjects.
Back to Steve's Home Page
This page last updated 22 April 1999.