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). Patients labeled "access/refractory" are strongly influenced by presentation rate, semantic relatedness of distractors, and repetition, yet they seem relatively unaffected by lexical frequency. "Degraded-store" patients, on the other hand, are strongly affected by lexical frequency but not by presentation rate, semantic relatedness, or repetition.
In our theoretical account of this pattern of data, language processes maintain and integrate semantic information over time, thereby compensating for the natural tendency of cortical neurons to habituate. Damage to parts of the language system responsible for semantic maintenance/integration has the effect of leaving semantic representations vulnerable to cortical habituation - producing the "access/refractory" pattern. Damage to semantic representations themselves leaves the compensation spared, producing the "degraded-store" pattern.