Posted: Jun 07, 2014 6:02 pm
by Bob@RealScienceRadio
crank wrote:The octopus has the circuitry on the backside, so does that mean that there must be a deficiency in that design?

Hi Crank, and others here at RS. Thanks for the welcome. ADParker, hi! Yeah, like everyone, my life is hectic and I already participate in various forums (which makes the time pressures really insane). I hope to reply to a couple other posts (which I haven't read yet but am eager to).

Crank, consider that the octopus and we humans have different functional requirements. When someone takes our photograph using flash photography, we've all noticed that we can't see well for a second or so. This is directly related to the "wiring" of our retinas. After the intense light of a flashbulb, your body needs to regenerate your photoreceptor cells. (Well, like the OPer, I'm not an expert in eyes either, so without looking up the terminology, I might get the vocabulary or a detail wrong, but I'm confident that the concept is correct.) An octopus doesn't have much of a chance of grabbing a quick look at the sun. And that's good for the octopus, because it doesn't have that direct blood supply on the side of its retina that it would need to rapidly regenerate those cells. So that octopus might be blind for an hour or more while its body struggled to transport to the receptors the nutrients needed for their regeneration.

We humans have both 1) an upright posture which causes us to gaze over the horizon without even trying, and we have 2) a mind that often brings us to override basic instincts, so that while we are wired to breathe, eat, to not stare at the sun, etc., humans can (and sadly, many have) overrode such an instinct and indeed, stared at the sun. If they do so for just an instant, they may loose their sight, but only for a second or so while the rich blood supply to the photoreceptor-cells side of the retina provides the nutrients for their rapid regeneration. If our retinas were wired like an octopus, that momentary blindness that we've all experienced, by necessity, would last longer, because the rich blood supply used for that regeneration would not be directly available. Blindness for minutes or hours after glancing at the sun might be sufficient to bring about a functional tradeoff of a blind spot, which most people are unaware of and we have to work to notice, as compared to a vulnerability, intermittent temporary blindness, which could even lead to death.

So Crank, with the engineering tradeoffs that are common in a physical universe, one can see that the functional spec of an octopus eye could call for wiring it in the opposite way of a human eye, without either being considered a deficiency.

- Bob Enyart