Connectionist approaches to understanding aphasic perseveration.

Aphasic patients make a variety of speech errors, including perseverations, in tasks that involve a linguistic component. What do perseverative and other errors imply about the nature of the neurologically damaged and intact language systems? Here we discuss the insights into the mechanisms of aphasic perseveration afforded by connectionist models. As a base for discussion, we review the Plaut and Shallice model of optic aphasic errors in object naming, which relies primarily on short-term learning mechanisms to produce perseverations. We then point out limitations of the model in addressing more recent data collected on aphasic perseveration and explain how incorporating information about the interaction of neuromodulatory systems and learning in the brain may help to overcome these limitations.