Eye dialect is the practice of fiction writers to spell words incorrectly in order to signal something about the character speaking the words. Often there is no difference in pronunciation (e.g., "wimmin" vs. "women"). The irregular spelling can indicate ignorance of the word on the part of the speaker. Seth Lerer gives the example of Twain's use of eye dialect in Huckleberry Finn when the Duke and Dauphin do Shakespeare, and the Dauphin asks what an "onkore" is; the reader is reading not so much the sound of the word but what the Dauphin is picturing in his mind when he says the word.
Eye dialect can be tricky; Joel Chandler Harris's use of it to render 19th-century African American speech is infamous. But it can also be evocative and effective. In The Knife of Never Letting Go, the YA novel about an illiterate society with no thought-privacy, the speech of the first-person narrator, teenage Todd, is rendered with eye dialect in phrases like "investigashun." Since Todd is largely illiterate, this doesn't even quite translate into "a picture of what Todd is imagining the word to look like in his mind." Instead, it's what Todd might imagine the word to look like if he were literate. Because in this society, literacy has been lost for so long that "correct" spelling would be lost, even if literacy itself were regained.