Thursday, March 7, 2013

Apperceptive vs. Associative: Will the Distinctions Make a Difference?

Apperceptive with elements of associative prosopagnosia. In plain English, that description essentially means Chuck cannot distinguish between faces he knows and those he doesn't, although he can recognize a face as such. Typically, this processing impairment results from damage to the right occipital temporal lobe -- the opposite side from Chuck's temporal lobectomy. In general, the associative aspect refers to his difficulty determining whether photos of two faces capture the same person or two different people, and then identifying someone from his or her photo. This memory "linking" impairment also is commonly associated with the brain's right anterior temporal region.

However, Chuck is left-handed -- or, more accurately, "mix-handed," which might have affected the location of face recognition functions in his brain. He's not exactly ambidextrous but he does perform a number of functions with his right hand. Did he develop that ability innately? Did his parents try to "re-train" him at a young age when he was performing tasks with his left hand? Did congenital damage to the right side of his brain prompt certain neurological functions to "migrate" to the left side? Any of these scenarios might have played a role in the development of his brain and the location of facial recognition centers. We'll never know the answer and, ultimately, it doesn't matter. The more important question is whether Chuck -- or potentially other prosopagnosia patients -- might benefit from the Face Training Program at the Human Vision and Eye Movement Lab in the University of British Columbia's Department of Ophthalmology and Visual Sciences.

This week's baseline visit to Jason Barton's lab offered some important clues. Over the course of four days, Chuck took a battery of tests.

Using the Cambridge Face Perception Test, he compared a "target" face to a range of similar faces, with one minute to rank the choices from farthest to closest to the target. 

The O'Toole Dynamic Face Recognition Test assessed his ability to identify short video clips of faces.

The "George" Component Test examined whether one of six facial features -- chin, forehead, eye size and distribution and mouth size and distribution -- was dissimilar in one face on a screen compared to two others.

The Cambridge Memory Test of Faces measured Chuck's ability to memorize faces shown in three orientations and then identify which of the faces he'd seen previously.

And the Warrington Memory Test of Faces and Words evaluated his ability to recognize previously seen faces and words.

Chuck also underwent a two-hour functional MRI, an electroencephalogram (EEG) and various ancillary studies, including face and voice matching, eye-tracking and word length effect.

Early results suggest Chuck performed below average in every test -- no surprise -- and no better than chance in some of them. In the components test, for instance, his performance was less accurate than random selection. Could the Face Training Program improve his score and, even more important, enhance his ability to identify the faces of family and friends in the real world? Only time will tell.

We'll be on our way home in the morning. The next step of Chuck's journey is just beginning.

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