The need to consider additional variables when summarizing agrammatism research

Throughout the history of aphasiology, researchers have identified importan t premorbid and stroke-related predictors of linguistic performance. Althou gh Grodzinsky discusses some of these variables, exclusion of other variabl es could lead to unnecessary experimental error and erroneous conclusions. Aspects to consider include sources of experimental bias, premorbid differe nces, nonlinguistic roles of the frontal regions, and comparison of normal and aphasic performance.