Verbal learning in semantic dementia: Is repetition priming a useful strategy?

Background: Semantic dementia (SD) is a neurodegenerative disease that impacts long-term conceptual and lexical knowledge (Hodges & Patterson, 1996). Severe naming difficulties are prevalent in SD, yet little is known about the potential for word learning in this population. Aims: We assessed patterns of repetition and implicit learning in patients with moderate to advanced SD via repeated exposure to word lists varied by frequency and imageability. We propose a tentative framework for the language loss incurred in SD and open a dialogue for treatment approaches targeted towards progressive semantic anomia. Methods and Procedures: In two experiments, we examined immediate serial recall and short-term learning in five patients with SD. We predicted reduced semantic effects (iinageability), preservation of lexical effects (frequency), and diminished primacy effects in serial recall, consistent with other semantically impaired populations (Martin & Saffran, 1997). We also predicted that severity of semantic impairment would modulate the facilitative effects of repeated exposure (i.e., repetition priming) on word list recall. Outcomes and Results: In immediate serial recall, all participants showed reduced imageability effects, but only one patient showed a significant word frequency advantage. Two patterns of serial position effects emerged: (1) poor recall of initial list items and (2) better recall of initial and final items. All participants showed minimal gains across repeated trials; however, patients who poorly recalled initial items showed the least benefit from repeated exposure. Conclusions: We discuss the usefulness of repetition-based interventions for SD and advocate maintenance of known vocabulary over reacquisition of forgotten words. We provide a theoretical framework for progressive language loss associated with SD; this model reflects an ordered reduction of lexical-semantic support coinciding with dementia severity.