Vernier Acuity

Here's a really neat thing we learned about in my psych class last quarter (disappointingly, one of the few neat things we learned). It's called vernier acuity. It's the ability to discern an offset in a supposedly continuous line. A related term is visual acuity, how small the smallest discernable visual feature is; it's analogous to the resolution at which we can view the world. This is affected by the size of a each cone on your retina.

You'd think that one is limited by the other. You'd think that our ability to detect an offset in a line is limited by our visual acuity, or how "pixelated" the world is to us as a function of the anatomy of our photoreceptors. Surprise! Vernier acuity has a resolution five to ten times greater than our visual acuity! WHAT?!? Where could all that extra precision come from?

This is an interesting demonstration of the critical role that visual processing systems in the brain play in how we sense our world. Our eyes don't just "tell" our brain how the world is put together. The brain must sort, refine, and compile the bits of data from photoreceptors into a cohesive image that we see. As a result, vernier acuity actually transcends the capable resolution offered by our retinas by somehow harnessing the computing power of the brain.

A further and slightly tangential question: as the brain processes raw sensory input signals from the retina, how can we be sure it is accurately tracking real world phenomena? What keeps the saliency of refinements in check if the only information we receive comes from our photoreceptors in the first place? How "real" is our "real"? Maybe our real is just what is most practical. (In other words, a possible answer to ponder: evolutionary advantage is given to those with certain visual interpretations, so these were the cortical processing systems developed).

A cool, INTERACTIVE (YAY! :D) demonstration can be found at the following link.

http://www.michaelbach.de/ot/lum_hyperacuity/index.html

I also used this source to supplement my ailing memory about the subject. Seems legit!

TLDR; We see with our brains (rather than strictly with our eyes) more than we might think. Vernier acuity is a really cool example of this.