When there is damage done to certain portions of the brain, the result is a language disorder called aphasia. The disorder impairs both the expression and understanding of language as well as reading and writing.
The three most common types of aphasia are:
Broca's aphasia: There is damage to the frontal lobe of the brain; those affacted by Broca's aphasia often omit small words such as "is," "and," and "the." For example, a person with Broca's aphasia would say, "Eat food" when they mean "I'm eating food" or "They want to eat food now." Individuals with Broca's aphasia are generally able to understand the speech of others to varying degrees.
Wernicke's aphasia: This results from damage to the temporal lobe. Affected individuals may speak in long sentences that have no meaning, add unnecessary words, and even create new "words." Individuals with Wernicke's aphasia generally have great difficulty understanding speech and are therefore often unaware of their mistakes.
Global aphasia: Results from damage to extensive portions of the language areas of the brain, and severely limits the communication and comprehension skills of affected individuals.
[http://www.nidcd.nih.gov/health/voice/aphasia.htm]
However, while these are the broad categories, each aphasia is unique. There are multiple types of language disorders grouped under the title 'aphasia' that vary subtly; for example, by afflicting certain word fields in contrast to others. However, the reasons for these subtle differences are not yet clear; despite the fact that there at least 1 million people in the US suffering from aphasia, we still have a very limited knowledge of the mechanisms of aphasia.
The article I read specifically details the case of John Hale, who was diagnosed with aphasia after suffering a stroke. His intelligence was unaffected, but he lost the ability to speak or write correctly. Although he partially recovered his writing after some years, his spoken repertoire consisted of sounds coming close to 'woah dawoah'. His aphasia was strange in that he didn't realize that he was making senseless sounds. He thought he was uttering meaningful sentences while pronoucing gibberish. This special condition in which the person is blind to his own failure in performing usual tasks (like uttering sentences) is called anosognosia. Ultimately, John Hale participated successfully in conversations by use of prosody (stress and intonation) and gestures, but nobody could understand the sentences he believed to had said. The article states, "It seems that the modules of the mind/brain which are responsible to self-monitoring became decoupled from those responsible to control of voluntary speech, respectively speech recognition...In John Hale's case, evidence was also found that -- as was the case with him -- loss of 'inner voice' (accompanying or slightly preceding speech as monitoring process) might be responsible for loss of speech, although read or heard words could be understood by him, and he supposedly could conceptualize what he wanted to say."
More than anything, reading this article makes me realize how much more we still have to learn in the field of neurology and linguistics. (Although in-depth testing of the language ability of individuals with the various aphasic syndromes will be very helpful in helping us achieve a more detailed understanding.) But this article brought up some really interesting points. For one thing, the fact that damage to a specific part of the brain can literally affect what kinds of words we are able to say--or not say--suggests that words register a certain way in our brain. That is, it's not just that we think about certain ideas with the left side of our brain, and certain ideas with the right side, but even the individual words we speak carry some sort of geographical weight in our brain. (Does that last sentence make sense?)The article also brought up the issue of anosognosia, which I'd never heard of before. I think it's so strange the way our brains will perceive something in a way that is so removed from reality. It's the same type of phenomenon that takes place when we hear our own voices; what we hear is different from what others hear when we speak. (Have you ever heard your own voice on an answering machine and not recognized it at all?)
[http://www.uzh.ch/neurol/psychologie/associates/maurer/landis.htm]
[http://metapsychology.mentalhelp.net/poc/view_doc.php?type=book&id=3850&cn=396]
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I think you make an important point that disorders like aphasia reveal the extent to which the brain can mis-represent reality. However, the key thing to note from a broader perspective is that what the brain is doing all the time is RE-presenting reality rather than simply presenting it as it is. Think about all of the cool visual illusions or sleight-of-hand tricks you have you must have seen over the course of your life; the reason these tricks seem like magic is that they exploit the way your brain processes and represents information from the external world so end up perceiving something that intellectually you know is not there and cannot be real. In this way, the aphasiac’s lack of ability to perceive their own speech stream is a product of how the brain works in general, and is different only in degree (and of course structural damage) from the way you or I perceive the world every day.
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