Complex sentence: Processing problems in auditory agnosia have been found to occur at different levels (12) (18) but although the damage can be either cortical or sub-cortical, it is debatable how much the condition is due to higher levels of processing.
Split into simpler sentences: Processing problems in auditory agnosia have been found to occur at different levels (12) (18). The damage can be ither cortical or sub-cortical, though it is is debatable how much the condition is due to higher levels of processing.