Although
an explosion blinded him at age 3, Michael May became a downhill
skier and went on to hold the world speed record. Then a
corneal stem cell transplant gave him back his sight and things started
to fall apart.
Since May’s successful surgery in March 2000,
UCSD psychologist Don MacLeod and Ione Fine, a UCSD postdoctoral
research assistant
now at USC’s Doheny Institute, have followed his progress.
In the process, they have uncovered some fascinating clues about
how the visual system works. Their study was published in the September
2003 issue of Nature Neuroscience.
Even though he could see for
the first three years of his life, May, now 45, experiences numerous
difficulties in navigating the
world
as a sighted person. While he is able to detect motion and color,
he has difficulty identifying objects and recognizing faces. Three
years after his surgery, he
still cannot identify his wife by her facial features. Rather,
he relies on other cues such as the length and color of her hair,
and
the way she walks.
One would expect sight to be a clear advantage—if
not a necessity—in
downhill skiing, but when May tackled the slopes after his operation
he was so overwhelmed by the amount of visual stimuli that he had
to close his eyes. When he was blind, May had the help of a guide
who gave him verbal directions on the slopes. These allowed him
to become amazingly adept at navigating obstacles. Although he
has made progress as a sighted skier, he continues to find it more
challenging than skiing as a blind man.
“
The difference between today and three years ago,” says May, “is
that I do a better job at guessing what I am seeing. What is the
same is that I am still guessing. I have been building a catalog
of the
visual
details around me and although this catalog is significantly more
filled out than it was two years ago, there seems to be an infinite
number of visuals to absorb.”
In their study, MacLeod and
Fine used brain scans (MRI) and other psychophysical and neuroimaging
techniques to measure the effects
of long-term blindness on the brain’s visual cortex. They
suggest that some visual mechanisms like processing motion are
hardwired
to a greater degree, and therefore may be more highly developed
early in infancy. Other more complex forms of processing, including
object
and face recognition, may evolve later in life and therefore may
not have had time to develop in people like May, who lose their
sight at such an early age.
The case study of Michael May reveals
the complex layers of perception involved in interpreting the world.
A brain that has been programmed
to navigate the world through touch, taste, smell and sound will
be challenged by the introduction of a new and very foreign sense—vision.
“
The old idea that there is one picture of the world on the surface
of the visual cortex is far too simple,” says MacLeod, who
is an authority on visual perception. “In fact, we probably
have a couple of dozen maps, each representing a different mode for
sensing and taking in our environment.” |
