Just like a stroke can affect the part of the brain that is associated with sight, it can also affect the part of the brain that has to do with speech.
Trouble speaking or even confusing ones words are signs of a stroke. Trying to speak but slurring one's words or being unable to speak are also signs that you could be having a stroke. Many people report feeling confused in mid conversation and can be unaware that they are suffering from a stroke.
Aphasia is the name for a communication disorder that is the result of damage or injury to a part of the brain, often caused by a stroke. As is characteristic of aphasia, it impedes a person's ability to use or understand words. It is important to note, however, that aphasia doesn't affect a person's intelligence, just the way in which they communicate. This can prove very frustrating for sufferers, because they feel as though they are always searching for the right word.