In the incredible story "Funes the Memorious" the eponymous Funes has an absolutely perfect memory, but is functionally mentally handicapped.

He can't even abstract to the existence of "trees" because he can recall and diff all of the details of every tree he's ever seen.

He can't even identify that he's seen a particular tree before, because he can diff how different it looked in a particular configuration of leaves and shadows because of different wind and cloud cover