Suppose we have some object, from which light rays reflect off and reach our eye. In this example, we can directly see this object, and the image is formed on our retina.
However, consider a coin kept under water. Due to refraction at the surface, we perceive the apparent depth and not the real depth of the coin. The ray of light bends at the surface, and when this new ray is traced backwards in a straight line, it converges at some height above the real depth.
My question is, why do we trace this new ray in a straight line backwards, instead of the original path that it took? This 'image' in a sense, works as a virtual object, and forms an image on our retina, that the original underwater object would have formed. Hence, we perceive this virtual object and see this, instead of the actual coin that is underwater,
Why is it so, that ray-tracing backwards, only work in straight lines, as if the refractive medium wasn't even there?
The same thing happens in a mirror. It appears to us, that the object is behind the mirror. This is the virtual image of the original object, and acts as a virtual object for our eyes, that form a real image on the retina.
Again my doubt is, whether this is just an illusion that our brain perceives? That our brains only trace the light backward in a straight line, even if the actual ray bent due to refraction, reflection or something? Our brain would trace the rays to some virtual object, which in the absence of any refraction or reflection, happens to be the real object. In the presence of these phenomena, this virtual object is an image of the real object, which is somewhere else. Is this just an illusion.
Is there some special reason, why our minds can perceive objects by tracing the light in a straight line backwards? For some reason, our brains don't trace the actual path of light, it only traces the light reaching our eyes in a straight line.
Best Answer
After reflection the rays seem to be coming in the direction that they would if there were an object on the left.
image from here
The brain chooses the most likely cause for the rays to be coming in that direction - and that's that there is an object on the left.
Exactly why it does that is a psychological question, but when humans were evolving mirrors weren't around, although the refraction in water effect, or reflection from still pools could have been seen.