Message #559

From: Melinda Green <>
Subject: RE: [MC4D] How many eyes?
Date: Sat, 13 Sep 2008 16:52:34 -0700


When you talk about animals and predator/prey strategies, you are
talking about real-world situations and not purely geometric ones, and
the difference is everything. I suspect that the need to instantly judge
the distance to prey as it briefly flashes past from any relative
direction makes binocular vision important. From your natural world
description, I think the best geometric reduction of your question is
the minimum number of eyes needed to determine the distance to a point
from a swivelable platform. In that one particular case I think that
your answer of two is correct.


Guy wrote:
> Thank you very much for your answer, Melinda.
> The motion parallax point is interesting but yes, it is cheating as
> far as answering my real question is concerned!! As you guessed, it
> was more the geometry than the psychology of perception that was
> challenging me!
> I think you have confirmed (tell me if I’ve misunderstood you) that
> two stationary eyes would suffice to see at least a /part/ of
> N-dimensional space in full N-D stereo, just as in 3D reality our two
> eyes allow us to see depth in a part of our visual field. Many
> predators remain stock still while they observe their prey. Herons,
> for example, stand motionless, bill poised over the water, waiting for
> a fish to move into spearing range (they have to deal with refractive
> depth effects too when they strike, of course!). If I understand you
> aright, a 4D heron would indeed only need two eyes for there to be a
> part of its visual field in full 4D, enabling it to strike with
> accuracy within that range.
> Most animals with good binocular vision are hunters – the hunted tend
> to have widely separated eyes pointing in different directions, like
> rabbits. Hunters only need really accurate depth perception in a
> limited field – namely, in the direction of the prey, for the final
> attack. So maybe predatory animals in N dimensions would be able to
> get away with just two eyes.
> Thanks again,
> Guy