In "The Metaphoric and Metonymic Poles," Roman Jakobson notes two types of aphasia, one to do with the inability to substitute, the other to combine -- in other words an incapacity with relation to similarities (metaphor)  or with contiguity (metonymy). 

"The development of a discourse my take place along two different semantic lines: one       topic may lead to another either through their similarity or through their contiguity. The

metaphoric way would be the most appropriate term for the first case and the metonymic way for the second, since they find their most condensed expression  in metaphor and metonymy respectively" (42)

He argues that milder forms of this aphasia can be detected in the verbal arts and that the uneven exercise of one pole can lead to the deterioration of the other (for which he cites an example of a Russian author prone to metaphor who, in his old age, exhibited traits of a similarity disorder - he split the idea of his self into his first and last names, unable to unite the two names, first and patronymic into a unified figure. An analysis of his writings reveals a tendency towards metonymy and synecdoche).  

Asking why there has not been more study of the two poles, Jakobson concludes that in metalinguistic practice "the researcher possesses more homogenous means to handle metaphor, whereas metonymy , based on a different principle, easily defies interpretation... Not only the tool of the observer but also the object of observation is responsible for the preponderance of metaphor over metonymy in scholarship." Thus he determines that literary study suffers from a contiguity disorder.