Mathieu Bouchard wrote:
On Mon, 22 Oct 2007, Martin Peach wrote:
No. The spokes just look blurred. Have you? If you try it at night under a streetlamp then you get the effect. I'm sure I have analog eyes ;)
You have seen a lot of analog equipment and you know that it does time-wise sampling. analog vs digital is not what we are debating.
Analog equipment works continuously in time. Digital is almost always clocked. If your eyes are clocked I'd like to see through them. If we are debating something here it involves a difference between continuous and discrete time systems, which constitutes part of the distinction between analog and digital in common parlance. Photons impinging on my eyes drive the illusion of vision. My eyes do not choose to sample incoming photons. The photons cause the nerve impulses. As long as the light source is continuous, something I am looking at will not spontaneously disappear because the rod or cone isn't sampling it at any given moment, rather the rod or cone is continually integrating the photon flux and outputting a stream of pulses in proportion to the incident intensity; the output is an analog of the input. In the brain the streams of pulses could be interpreted as digital but the streams from all the receptors are not synchronized by a central clock so the overall effect is of a continuous-time system.
anyway, analog electronics are what one uses to construct digital electronics, thus analog electronics are very capable of discontinuity. If you are not satisfied with thinking of human vision as electric, you can extend the same reasoning to chemical processes that complement the electric processes in use by neurons.
I never said any of that. I was responding to your implication that the aliasing effect seen in the spokes of a spinning bicycle wheel is caused by some sort of discrete-time sampling process in the eye, which is not the case. The aliasing is induced by illumination by a periodic light source which the mind interprets using a "most likely" scenario in which a spoke that reappears closest to one that was previously visible is probably the same spoke.
Martin