The occipital (and lower part of the temporal) lobes are devoted to vision. Primary visual cortex is directly related to sight, and damage to it produces a hole in a persons visual field Ö a scitoma.
A scitoma is sometimes used as a metaphor to both reflect a perception disorder, and, by extension, to imply that due to this disorder one just canít understand certain things.
Generally stating that someone has a scitoma it is not intended as an insult, but just as an observation of fact. Of course, that's not to say it can't go the other way....