When my daughter was born, I was fascinated with the method by which the pediatrician tested her hearing. Being used to the old procedure of “put these giant headphones on and raise your hand when you hear the beep”, I thought, how the heck are they going to test an infant who is less than 2 days old? I don’t remember all of the details, but basically her brain waves were measured to determine if she was hearing a specific sound. Cool!
So, this got me thinking. Is there a similar procedure for testing vision?
My neice was pronounced legally blind shortly after birth. AFAIK there is no brain wave test for vision. She underwent some major testing at a very good hospital at 2 months old and brain waves were not part of it. The vision test was mostly her physical reaction to lightness and darkness.
Hmm… I think maybe it’s because most of the processing of sound takes place in the brain. The eardrum-hammer-anvil-stirrup-cochlea being mainly an elaborate transmission of sound to the nerves that actually do something with it. Which would explain why you can stick wires into a cochlea, run them over to the hearing nerves, and wind up with something the brain can process into recognizable sound. But if the mechanism isn’t working little data gets through and the relevant parts of the brain are “quiet”.
Vision, however, seems to be a more complex processing problem. There’s a whole bunch of stuff that has to happen, involving bending and focusing light through the cornea and lens, the density of cells in the retina, whether or not those cells respond properly, some evidence prelimary processing of signals might start in the retina itself… all this before-the-brain stuff can get screwed up enough to prevent useful vision (resulting in legal blindness) but still get enough stimulation through to generate activity in the visual system of the brain. So you can be legally blind but still have a surprising amount of vision. Which means the visual processing parts of the brain in a visually impaired person can be humming along in a manner indistinguisable from a normally sighted person.
On the other hand, I’m not a doctor or visual researcher so I could also be off base on this.
IANAMD, but I’ve heard of the evoked potential test for vision. I’ve come across this where people claim that they’re blind, that they can’t even see a hand in front of them. (I know legal blindness is 20/200 or greater, but this comes up when people claim no vision.) There are electrical charges, of course, in the cerebral cortex which are produced by stimulation of a sense organ. So, it appears to me that there is a simular test for vision as for hearing.
Of course, a small child would have no reason for faking blindness, so that’s why Zumba’s niece was not further tested.