Is Optical Illusion a Misnomer in Physics Discussions?

[bahamagreen]

Maybe I'm missing something - why is what the observer gets as a "measurement" and what the observer would "see visually" not the same? The measurement would have to be done with light, right? If so, how is the measurement light different from the visual light (to get the shape difference)? If not, what is used to measure it?

I still think the captions are clumsy. The "b)" is the only one that does not mark the end of a section that refers to it, but appears in the middle of its section.

 

[wabbit]

I would say the difference lies in how he interprets the data. The observer doing a measurement could very well do it from those same camera frames showing a round ball plus a few auxiliary measures or data. But the equations he uses do not say that the size of the object is directly proportional to its apparent width - instead he will apply formulas that take into account both time delay and length contraction, to convert the raw measurements to results about the actual shape of the object.

This isn't a fundamental difference - our brain also constantly applies complex algorithms to infer "true shape" from the raw image it receives from the retina (as many visual illusions demonstrate, the image we see is not the image on the retina), It isn't trained to do relativistic corrections though.

 

[zoobyshoe]

Here's an example of an optical illusion in which brain processing is actually injecting a perception that is not relevant to reality (a green dot). Stare at the crosshair and you should see the green dot. This is different than geometrical arrangement - you're actually perceiving something that's not there, presumably due to opponent process theory of color perception.

That's an alarmingly strong illusion. And a circle of green dots persists in my visual field when I look away.

 

[Pythagorean]

That's an alarmingly strong illusion. And a circle of green dots persists in my visual field when I look away.

Here's an even more interesting one. The afterimage changes color when the shape rotates - and it's all in your head! What the heck!? (stare at the dot as normal)

 

[wabbit]

My visual cortex begs you to stop, sir : )

 

[zoobyshoe]

My visual cortex begs you to stop, sir : )

Being a more direct articulation of what I meant to express in my post #38.

 

[A.T.]

Maybe I'm missing something - why is what the observer gets as a "measurement" and what the observer would "see visually" not the same?

Visual impression is affected by signal delay. Measurement means that you remove such known artifacts.