pz

Hmmm. I saw the question and seem to have a completely different perspective on the problem than everyone else. My first thought wasn't about wavelengths, but information processing and reduction. Of course, a trillion is still a bit high -- I think the original author just made up the number.

The retina is not a camera. It forms as an outpocketing of the brain and contains some extremely complex neuronal circuitry, organized in multiple layers of processing power. Photoreceptors are only the first stage, and the intermediate layers do some very sophisticated stuff, comparing the output from a wide field of receptors, enhancing edges and contrast, integrating recent history to detect motion, and adjusting the signal amplitude to allow us to sense over a wide range of intensities. The final stage, the retinal ganglion cells, represent a 100- to 1000-fold reduction in cell numbers from the photoreceptors.

The information going back through the optic nerve is not a 2-D spatial map of intensities. It's something much stranger, containing coded signals that describe overall intensities, spatial frequencies, movement, contrast, edges and their orientation, etc. And it just gets even weirder -- as the information passes through thalamic relays, there is integration of inputs from both eyes to begin to build a 3-D map. We also begin to get a divergence of information: neurons extract specific bits of the signal (binocularity, for instance, or motion or orientation) and distribute that back to specific regions of the brain for further processing.

Once you try to follow the circuitry of visual processing, you will quickly realize that it's not as simple as generating a photograph of a scene and showing it to the little homonculus of your consciousness. The eye abstracts key elements of the scene, deeper processing centers blow it to flinders, dissecting out various parameters of the signal, and what your consciousness is actually doing is reconstructing visual scenes on the fly from data that has been massaged to an extraordinary degree.

I wouldn't entirely agree with the idea that only a trillionth of the received information makes it through, but the statement that "We obviously cannot see what is really out there" is a gross understatement.