Farah reviewed approximately 100 cases of associative agnosia and
focused on their abilities with words, objects, and faces. Intriguingly,
she found all combinations of deficits except for two combinations.
There were no cases of object agnosia without prosopagnosia and
alexia and no cases of alexia and prosopagnosia without object agnosia.
This led to her influential proposal that there are two shape representation
systems. One mechanism constructs structural descriptions for objects
that are decomposable into numerous parts such as words, whereas the
othermechanism constructs structural descriptions for objects that
allow little shape decomposition such as faces and so must be represented