Freud's familiarity with the work of the eminent neurologist J. Hughlings Jackson enabled him to make substantial contributions to aphasiology and inspired Freud's earliest insights into the emotional determinants of speech disruptions. However, Jackson's hierarchical model, which came to dominate Freud's topographic system of mental organization, created a number of insoluable difficulties in the early psychoanalytic writings. Despite the contention of some that Jackson's influence lent additional rigor to Freud's cognitive psychology, it is argued that the Jacksonian trend in Freud's thought contributed to a narrow notion of repression based on rather untenable notions of how thoughts attain or do not attain consciousness. It contributed also to certain problems in the dream theory, particularly regarding the role of language in dreaming.