Wednesday, June 29, 2011
Ventral stream damage/ visual agnosia
The topic I would like to report on is about damage to the ventral stream which typically leads to visual agnosia. Although the text goes into some detail about the function of the ventral stream and what repercussions one would endure if that stream were injured or damaged, it is always interesting and beneficial to look into real life examples to gain a better understanding for the types of damages and limitations those who have suffered from a damaged ventral stream endure. The case that I chose to look at was of a man (who the article on http://brain.oxfordjournals.org/content/125/1/58.full, referred to as S.B.), 30 years of age at the time of research and study, who suffered from meningoencephalitis when he was just three years old. meningoencephalitis is a disease that resembles aspects of both meningitis (inflammation of the meninges) as well as encephalitis (inflammation of the brain). The disease left S.B. with major damage to the ventral stream as well as damage in the right dorsal pathway. From there on out S.B. had immense trouble with visual recognition and visual agnosia (which is partial or total inability to recognize objects visually). At first, doctors assumed that S.B. was completely blind due to his inability to recognize familiar faces and objects from his everyday life. At a second glance though, S.B. also displayed many contradictory recognizances as well which lead doctors to believe that S.B. was not in fact blind but instead had very distinct and limited visual acuity and recognition. S.B. received a formal education through a school for the partially blind and strived to live as normal a life as he could. Upon entrance into the center where this research took place, S.B. was not able to recognize virtually any familiar objects by sight but could still identify them by touch. S.B. was even perfectly capable of reading braille. What would come as a shock to most of us not very familiar with this impairment though, is the amount of activities and everyday tasks that S.B. was able to participate in and carry out succesfsully. For example, what came as most shocking to me was the fact that S.B. could maneuver and drive a motorcycle ( a task that even some fully functioning individuals with no impairment whatsoever may even have a hard time doing). Other activities that came extremely easily to S.B. were things such as goal keeping, tennis, swimming, juggling and other physically demanding sports as well. Of course, S.B. went through years of tests that were explained throughout the article, but one of the more interesting findings from these tests, aside from S.B's physical capability to maneuver in an environment and utilize motion to complete certain tasks, is the finding that he was also able to draw certain objects (mainly those he knows by touch). One would assume due to the fact that S.B. can not even identify most common objects he would not be able to replicate them in a drawing, but this proved to be untrue for S.B., making his specific case all the more interesting as well!
the video link above shows a patient with visual agnosia attemping to recognize a very common household object (I apologize for the poor quality)
the link above is where I first read about the study done of S.B. An interesting add on to this is the 3D image of S.B.'s brain (Figure 1) which shows the exact areas of the brain which were found to be negatively affected through an MRI.
by: Lindsay Mauser