Mirrors Don’t Lie. Mislead? Oh, Yes.

[groovedaddy]

For the bubbleheaded young Narcissus of myth, the mirror spun a fatal fantasy, and the beautiful boy chose to die by the side of a reflecting pond rather than leave his “beloved” behind. For the aging narcissist of Shakespeare’s 62nd sonnet, the mirror delivered a much-needed whack to his vanity, the sight of a face “beated and chopp’d with tann’d antiquity” underscoring the limits of self-love.

Whether made of highly polished metal or of glass with a coating of metal on the back, mirrors have fascinated people for millennia: ancient Egyptians were often depicted holding hand mirrors. With their capacity to reflect back nearly all incident light upon them and so recapitulate the scene they face, mirrors are like pieces of dreams, their images hyper-real and profoundly fake. Mirrors reveal truths you may not want to see. Give them a little smoke and a house to call their own, and mirrors will tell you nothing but lies.

To scientists, the simultaneous simplicity and complexity of mirrors make them powerful tools for exploring questions about perception and cognition in humans and other neuronally gifted species, and how the brain interprets and acts upon the great tides of sensory information from the external world. They are using mirrors to study how the brain decides what is self and what is other, how it judges distances and trajectories of objects, and how it reconstructs the richly three-dimensional quality of the outside world from what is essentially a two-dimensional snapshot taken by the retina’s flat sheet of receptor cells. They are applying mirrors in medicine, to create reflected images of patients’ limbs or other body parts and thus trick the brain into healing itself. Mirror therapy has been successful in treating disorders like phantom limb syndrome, chronic pain and post-stroke paralysis.

“In a sense, mirrors are the best ‘virtual reality’ system that we can build,” said Marco Bertamini of the University of Liverpool. “The object ‘inside’ the mirror is virtual, but as far as our eyes are concerned it exists as much as any other object.” Dr. Bertamini and his colleagues have also studied what people believe about the nature of mirrors and mirror images, and have found nearly everybody, even students of physics and math, to be shockingly off the mark.

http://www.nytimes.com/2008/07/22/science/22angi.html?th&emc=th

[Jim__]

1. The most surprising thing in the artilce to me:

... Outline your face on a mirror, and you will find it to be exactly half the size of your real face. Step back as much as you please, and the size of that outlined oval will not change: it will remain half the size of your face (or half the size of whatever part of your body you are looking at), even as the background scene reflected in the mirror steadily changes. Importantly, this half-size rule does not apply to the image of someone else moving about the room. If you sit still by the mirror, and a friend approaches or moves away, the size of the person’s image in the mirror will grow or shrink as our innate sense says it should.

I didn't know that, and I wouldn't have guessed it.

[unpossibles]

2. I would imagine it's because the face you are seeing (your own) is "twice as far away" as the mirror

does that make sense?

I've noticed this effect before, but had not really thought about the why until just now.

[Jim__]

3. Yea, that's pretty much it. But, I never realized it. - n/t

[MrMonk]

4. Here's something I've noticed, but haven't been able to explain:

standing away from a mirror, with my glasses on, I see both my face and the background clearly;
standing away from the mirror, with my glasses off, both my face and the background are blurred;
moving closer to the mirror, with my glasses off, my face appears more clearly, but the background remains blurred.

Common sense seems to tell me that both my face and the background should appear more clearly, since the light from each is reflected from the same surface that I'm looking at.

[Jim__]

5. My guess at what's happening ...

... the light that is coming from the background, reaches the mirror in the same state of diffusion that it would reach your eyes if you were standing where the mirror is and looking at the background. So, your eyes see the image the same way they would see it if you were looking at it directly from the position of the mirror (and then a little more blur for the distance from the mirror back to your eyes).

[MrMonk]

6. That makes sense ...

If I look at the events from the perspective of someone in the mirror looking back at me:
with their glasses on, they would see me (standing away from the mirror) and the background clearly;
with their glasses off, they would see me (standing away from the mirror) and the background blurred;
with their glasses off, and me moving more closely to the mirror, they would see my face more clearly, but they would still see the background blurred, since it was still just as far from them.