The condition that Madeleine Stowe's character suffers from the film does actually exist. It's called retroactive hallucination.
Madeleine Stowe's character was originally a poet, but Stowe asked if the script could be changed to make her a musician. Stowe then learned how to play the violin for the role.
Madeleine Stowe visited doctors at UCLA to study blindness. Aidan Quinn and James Remar spent time with members of the Chicago Police Department, and the line "We will solve no crime before there's overtime" was provided by some of the officers.
The lines quoted by Hallstrom 'For the soul is dead that slumbers,/ And things are not what they seem.' are from A Psalm of Life by Henry Wadsworth Longfellow (1807-1882) and was first published in the Knickerbocker Magazine in October 1838.